Prediction
of Successful Amorphous Solid Dispersion
Pairs through Liquid State Nuclear Magnetic Resonance
Introduction In the last 20 years, there has been an increase in the number of poorly water-soluble drugs in the pharmaceutical pipeline that require enabling formulation technologies to provide sufficient oral bioavailability. , As a result, new strategies to improve oral drug solubility, such as amorphous solid dispersions (ASD), have become a greater focus. In an ASD, the amorphous form of the drug is dispersed in a polymer. The goal of ASD is to deliver a supersaturated concentration of the drug to the gastrointestinal (GI) tract, leading to increased drug absorption. However, the supersaturated drug is physically unstable and prone to precipitation from solution, rendering it unable to be absorbed. To delay precipitation and avoid precipitation, excipients, such as polymers, are used. Ideally, these polymers also maintain amorphous drug in the solid state, avoiding drug crystallizing on storage. Once introduced into the GI tract, polymer aids dissolution and prevents drug aggregation in the aqueous environment by limiting drug molecular mobility in solution and interfering with crystal lattice nucleation and growth. − Therefore, a successful ASD not only promotes drug supersaturated concentrations (i.e., via spring effect) but also delays drug precipitation (i.e., via parachute effect). , , In preclinical formulation development, drug is available in limited quantities, and nondestructive methods that can be conducted using small drug quantity are preferable. Common polymer screening strategies currently used for ASD development consume the drug sample, including film casting techniques and supersaturation studies. , − Taking into consideration this scarcity of drug, liquid state nuclear magnetic resonance ( 1 HNMR) provides a modality for high-throughput screening of polymers for ASD formulations that would not consume the drug sample and would allow for multiple experiments. 1 HNMR has been previously used as a tool to understand molecular interactions between drug and formulation components, including polymers. − , − We aim to expand the utility of 1 HNMR to streamline polymer selection for ASD. Our work aims to make polymer screening more rapid by focusing on drug–polymer pair interactions and by reducing the required drug amount for performing tests. Potentially, 1 HNMR advantages in aiding polymer selection include specificity, spatial selectivity, and high sensitivity to environmental changes and molecular mobility. The goal of this study was to devise a 1 HNMR approach that identifies viable polymers that promote supersaturation and prevent crystallization of etravirine. NMR results were compared with supersaturation experimental results. Our hypothesis is that strong molecular interactions between polymer and drug in 1 HNMR anticipates reduced precipitation kinetics in supersaturation studies. Interactions here were assessed by saturation transfer difference nuclear magnetic resonance (STD-NMR) and T 1 relaxation time. Precipitation inhibition was assessed by supersaturation studies using a solvent-shift methodology. The motivation for this work is based on previous literature where hydroxypropyl methylcellulose acetate succinate grade H (HPMCAS-H) inhibited carbamazepine precipitation due to strong intermolecular interactions between drug and polymer which were observed via NMR spectroscopy and confirmed by supersaturation studies. STD-NMR experiments are commonly used in early drug discovery for the ligand screening of large molecules such as proteins. This 1 HNMR technique is highly sensitive to intermolecular interactions, and it is a tool to characterize ligand–receptor complexes through changes in the ligand, for example, via ligand peak intensity. STD-NMR can provide insight into binding affinity and binding regions of the ligand. − In addition to STD-NMR, changes in the proton T 1 relaxation time can provide information on binding complexes. Protons involved in a ligand–protein complex will display a decrease in T 1 relaxation time compared to their T 1 times without the large molecule present. − These two techniques could be useful in determining binding between the drug and polymers. Etravirine was chosen as the model drug because it is poorly water-soluble and commercially available as an ASD. Intelence from Janssen is formulated with hydroxypropyl methylcellulose (HPMC) and presumably reflects strong molecular interactions between etravirine and HPMC. Of note, previous supersaturation studies showed that HPMCAS-L grade provided the greatest precipitation inhibition of etravirine among several polymers. Therefore, the polymers chosen to be studied here were HPMC, HPMCAS-M, and copovidone (PVP-VA). These are chemically diverse polymers and are widely used in ASD formulation.   Experimental Section 2.1 Overall Study Approach This study focused on expanding the use of 1 HNMR techniques, specifically STD-NMR and T 1 relaxation time, in relation to the drug, to identify polymers that promote drug supersaturation and inhibit crystallization. The overall study approach is shown in . Through STD-NMR and T 1 relaxation time experiments, the etravirine binding strength and etravirine binding epitope with HPMC, HPMCAS-M, and PVP-VA were determined at different drug concentrations. Strong molecular interactions between polymer and etravirine in 1 HNMR were anticipated to reduce the precipitation kinetics in supersaturation studies. Polymers that were expected to promote supersaturation and inhibit etravirine crystallization were identified via 1 HNMR. 1 HNMR results were then challenged through supersaturation studies. The supersaturation studies were conducted by using the solvent-shift methodology. Supersaturation indices such as time to precipitation, degree of supersaturation, and the excipient gain factor (EGF) were calculated. 2.2 Materials Etravirine was purchased from ChemShuttle (Burlingame, CA). HPMC (Affinisol HME 15LV) was provided by DuPont (Wilmington, DE). HPMCAS-M (Aquasolve) was gifted by Ashland (Covington, KY). PVP-VA (Kollidon VA 64) was gifted by BASF (Ludwigshafen, Germany). Barnstead GenPure purification system (Thermo Scientific; Waltham, MA) provided purified water. Fasted state simulated intestinal fluid concentrated powder (FaSSIF) was acquired from Biorelevant (London, UK). Sodium phosphate monobasic, sodium hydroxide, sodium chloride, hydrochloric acid, and dimethyl sulfoxide-d6 (DMSO-d6) were acquired from Sigma-Aldrich (St. Louis, MO). Deuterium oxide with 0.03% trimethylsilylpropanoic acid (TSP) was acquired from the Cambridge Isotope Laboratory (Tewksbury, MA). NMR tubes (500 MHz, 5 mm, Standard Series) were acquired from Norell (Morganton, NC). 2.3 NMR Sample Preparation and Sample Concentration Solution of etravirine with and without polymers was prepared in 70% DMSO-d6 and 30% D 2 O (0.03% TSP). This solvent proportion was used to ensure total etravirine and polymer solubility. Lower DMSO concentrations were tested but did not solubilize etravirine. The lowest concentration of etravirine that would ensure an appropriate signal-to-noise ratio and reasonable experimental time was approximately 100 μM. 70% DMSO was the lowest concentration of DMSO needed to solubilize etravirine. TSP was used as an internal reference. To better understand the interaction of etravirine and polymer, STD-NMR and T 1 experiments were run with four levels of etravirine concentration. The weight-based (w/w) proportions of etravirine to polymer were 1:1, 2:1, 3:1, and 4:1. The relative abundance of polymer impacts the relative abundance of polymer fragments that may interact with the drug. Etravirine and polymer structures are shown in . Based on the estimated ranges of polymer molecular weight provided by the manufacturers, we used an average molecular weight of 90,000 g/mol for HPMC, 103,200 for HPMCAS-M, and 50,000 g/mol for PVP-VA. The polymer concentrations were fixed at 0.5, 0.6, and 1 uM for HPMCAS, HPMC, and PVP-VA, respectively. shows the specific etravirine and polymer concentrations for each of the four concentration levels in the NMR experiments. 2.4 NMR Experiments and Analysis All NMR experiments were performed in a Varian DD2 500 MHz NMR (Agilent, Santa Clara, CA) at 25 °C. Data processing and analysis, as well as spectrum figures, were performed in NMRBox, using OpenVnmrj (Version 2.1A) and MestReNova (Mnova, Version 14.3.1-31739), respectively. Both VNMRJ and Mnova were part of the NMR Box. Etravirine, HPMC, HPMCAS-M, and PVP-VA structures are presented in . Etravirine reportable protons are numbered from 1 through 4. 2.5 1 HNMR Peak Assignment Experiments Experiments with etravirine and polymers were performed to assign the proton peaks to specific protons in the etravirine structure and to determine the location of etravirine and polymer proton peaks in the spectrum. Single-pulse proton experiments (vendor-supplied pulse sequence, s2pul, was used) were acquired on etravirine and each of the polymers separately. Spectral width was set to 6009.28 Hz (e.g., 12 ppm, −1 to 11 ppm) and with the transmitter offset at 5 ppm. Relaxation delays of 1.5 s were used. The number of transients acquired was 512. The 90° pulse was set to 7.625 μs at 56 dB. The TSP peak was set to 0 ppm and used as chemical shift reference. HMBC, HMQC, and 13 C NMR were used to assign protons in the etravirine spectrum. The parameters for these experiments are shown in Table S1 . 2.6 STD-NMR Experiments The basic STD experiment consisted of a saturation transfer step, delivered by low-power Gaussian-shaped pulses of narrow bandwidth and centered at a selected frequency that alternated between setting followed by a high-power broadband pulse, one on-resonance exclusively at the macromolecule, and one at off-resonance (reference) from all signals. The signals from the on- and off-resonance pathways were stored separately (vendor-supplied pulse sequence of dpfgse-satxfer2). The results from the difference between on- and off-resonance pathways were generated by subtracting the separate fid files. Spectral width was set to 6009.28 Hz (e.g., 12 ppm, −1 to 11 ppm) and with the transmitter offset at 5 ppm. Relaxation delays of 1.5 s were used. The number of transients acquired was 512 and preceded by 4 steady-state acquisitions. The 90° pulse, calibrated for each sample, was typically about 7.625 μs at 56 dB. The TSP peak was set to 0 ppm and used as chemical shift reference. The saturation transfer pulse train consisted of various number of cycles of a 50 ms Gaussian-shaped pulse at −3 dB and a 1 ms interpulse delay, summing up to 0.5, 1, 2, 3, 4, and 5 s of saturation time. The saturation frequency on-resonance with the polymer was set at 3.5 ppm, and the off-resonance was set at 20 ppm. Additional STD-NMR experiments with saturation frequency at 1.7 ppm in samples with PVP-VA were conducted to assess robustness of saturation transfer studies at 3.5 ppm ( Figure S1 ). The STD results using 1.7 and 3.5 ppm were similar. In addition to the experiments with etravirine and polymers, control experiments with only etravirine at concentrations of 237 and 496 μM were conducted to check for the presence of signals in the absence of polymers. The STD-NMR experiments were divided into two parts: on-resonance and off-resonance experiments. During the on-resonance experiments, samples with etravirine and polymer were irradiated with an energy pulse at a selective frequency (3.5 ppm). This frequency corresponded to the protons in the polymer structure. Additionally, this frequency avoided applying energy near etravirine protons, more specifically proton H1 (2.16 ppm). In the off-resonance experiment, the saturation-transfer pulses were away from all signals, from the polymer or drug structure (20 ppm). In the on-resonance experiment, the polymer structure was saturated by selective radio frequency (rf) irradiation. Energy was transferred (i.e., saturation transfer) from the polymer to its surroundings, including, if any, small molecules that were bound specifically to the polymer, through spin diffusion (nuclear Overhauser effect). The STD-NMR signal intensity ( I STD ) was calculated by subtracting the proton peak intensity of the off-resonance spectrum ( I 0 ) by the respective proton peak intensity in the on-resonance spectrum ( I SAT ), as outlined in Viegas et al. . Therefore, only etravirine protons that received the saturation transfer were expected to show an I STD . I STD was an indication of binding between the site of saturation transfer in the polymer to etravirine protons that are within 5 Å to the polymer. , Etravirine protons that were close to the polymer were expected to show higher peak intensities in the difference spectrum (i.e., high I STD ). Protons that did not receive any saturation transfer from the polymer were expected to show the same peak intensities in the on- and off-resonance spectra and show zero I STD . In order to calculate I STD , both on- and off-resonance spectra were recorded on the same vertical scale. 1 The approach to describe the interaction between polymer and drug is to calculate the STD amplification factor ( A STD ) of a given proton in the drug structure. A STD for each of the reportable etravirine protons is calculated by where [ D ] is the drug concentration (i.e., etravirine concentration) and [ P ] is the polymer concentration in moles. 2 A STD represented the magnitude of saturation transfer from the polymer to etravirine. For a specific saturation time, A STD denoted the average number of drug molecules saturated per molecule of polymer. Etravirine protons closer to the polymer were expected to present a higher A STD . In addition, for the drug protons involved in binding, their A STD increased as a function of the saturation time. As saturation time increased, there was a greater turnover of etravirine molecules in the polymer binding site, leading to an increase in I STD signals and consequently an increase in A STD values. Although ASD formulations usually have an excess of polymer by weight in relation to the drug, the STD-NMR in this study followed the methodology applied to screening protein binding ligands. In this methodology, the large molecule (e.g., polymers, proteins) was irradiated with a rf pulse and the energy was transferred to nearby small molecules (e.g., drugs, ligands in general). The small molecule needed to be in excess of the polymer because the energy saturated small molecules (i.e., molecule that received saturation transfer from the big molecule) needed to detach themselves from the large molecule in order to release the energy signal that will be detected by the NMR instrument. STD-NMR was applicable to binding complexes with dissociation constant ( k off ) in the millimolar to micromolar range. 2.7 T 1 Relaxation Time Measurements T 1 relaxation time of each proton, also known as the spin–lattice relation time, in the etravirine structure was measured in the absence and presence of polymers. In order to streamline the experiments, the same samples used for STD-NMR experiments were also used for T 1 experiments. Control samples for T 1 experiments did not contain polymers and had the same amount of etravirine as the samples with polymers. The number of scans used in the T 1 experiments was 16. Spectrum width, transmitter offset, number of points in the spectrum, and number of steady-state transients were the same as those for the STD-NMR experiments. T 1 relaxation time was calculated using the inversion recovery method. The time delay [e.g., Tau (τ)] between the inversion pulse and the recovery pulse, as well as the relaxation delay between transients, were optimized based on preliminary T 1 measurements to estimate the shortest and the longest T 1 values. The estimated longest T 1 was used to set the relaxation delay between transients to five to six times the longest T 1 estimate. All T 1 values reported were calculated with a vendor-supplied macro called “ T 1 ” in the OpenVnmrj software. Multiple spectra were collected with different τ values (array of 10–12 τ values), and a nonlinear regression was fitted to obtain T 1 time estimate for each proton using : 3 where M z (τ) is the net magnetization vector along the z -axis at time τ and M 0 is the equilibrium magnetization. After a radio frequency pulse was applied to the protons, the energy traveled from the proton (i.e., spins) to the environment (i.e., lattice), resulting in the return of the spins to the equilibrium state. The T 1 relaxation time was the time that it took for the protons to recover to approximately 63% of their equilibrium magnetization. T 1 relaxation time varied from proton to proton depending on the other atoms in the environment, molecular bonding, solvent, temperature, and other components outside of the molecule that are interacting with the proton. Etravirine protons involved in interacting with the polymers lose energy faster (i.e., small T 1 relaxation time) than do the protons not involved in binding. Therefore, this approach determined which polymers interacted with etravirine molecules. We assumed that specific interactions between etravirine and the polymers provided additional pathways for etravirine protons to dissipate energy and thereby return to equilibrium in a shorter time, as measured by a shorter T 1 . A survey of the T 1 times of the etravirine protons in the absence and presence of polymers was used to identify such energy transfers. 2.8 2D- 1 H NOESY Experiments Data from 2D- 1 H NOESY experiments were collected on etravirine in the presence of each of HPMCAS-M and PVP-VA, as well as control samples of each of the polymers by themselves at 25 °C. Etravirine and polymers were at a concentration of 1.5 mg/mL each and in the presence of 70% DMSO/30% D 2 O. Mixing times used ranged from 100 to 500 ms. The total number of points used to record the fids were 2048; spectral width of 12.5 ppm centered at 5.8 ppm was used for both dimensions. A delay between transients of 2 s was used, and 32 transients were acquired per fid. The number of increments acquired in the indirectly detected dimension varied from 200 to 256. The NMR data were processed in NMRPipe (Version 11.5) and viewed in Sparky (Version build_04-22-2021) (NMR Box). 2.9 Viscosity of NMR Samples Viscosity measurements were performed with a Discovery HR-2 Rheometer (TA Instruments, New Castle, DE). Samples (300 μL) of etravirine in 70% d6-DMSO/30% D 2 O with and without polymers were analyzed. Samples without the drug and polymer were also analyzed. The concentration of the samples was 4:1 etravirine:polymer, as shown in . Temperature was at a constant temperature of 25 °C and was controlled by a Peltier plate. The bottom plate diameter and cone angle were 40 mm and 1.007°, respectively. The shear rate varied from 1000 to 1400 s –1 . Apparent viscosity was calculated as shear stress over the shear rate. 2.10 Preparation of FaSSIF The buffer for FaSSIF preparation was made by dissolving 0.420 g of sodium hydroxide, 3.438 g of sodium phosphate monobasic anhydrous, and 6.186 g of sodium chloride in 0.9 L of purified water. The mix was stirred for 10 min, and then, the pH was adjusted with hydrochloric acid or sodium hydroxide to a pH of 6.5. Additional water was added to make 1 L of the total volume. Buffer was added to 2.240 g of FaSSIF concentrated powder, and the mixture was stirred for 2 h. FaSSIF media was stored at RT and used within 48 h of preparation. 2.11 Determining Etravirine Equilibrium Solubility An excess of etravirine was added to 10 mL of FaSSIF that was shaken at 37 °C for 24 h ( n = 6). The media pH was checked, and no change from initial pH conditions was observed. Samples were filtrated with a 0.45 μm PVDF filter, with the first 1 mL being discarded and 1 mL collected for analysis. After filtration, 0.5 mL of sample was evaporated under N 2 at 45 °C. Samples were reconstituted with 100 uL of mobile phase. Samples were analyzed by an isocratic method using 80% methanol and 20% water in a Waters AcquityH Class UPLC system (Waters Corporation; Milford, MA) coupled with a vacuum degasser, quaternary pump, and autosampler. Column used was Poroshell 120 EC-C18 (4 μm, 4.6 mm × 150 mm; Agilent) at 30 °C, flow rate was 1 mL/min, total run time was 4.5 min, and retention time was 3.2 min. The PDA detector was set to a wavelength of 310 nm. 2.12 Supersaturation Studies Using Solvent-Shift Methodology and In Situ UV System Etravirine supersaturation studies were conducting using the solvent-shift methodology which was adapted from other publications. , , , , Etravirine concentrations were measured using the Pion μDiss Profiler (Pion, Billerica, MA) coupled with the Pion Rainbow R6 system (Pion Inc.; Billerica, MA) with six probes (2 mm probe size) and analyzed using AuPro Software (ver. 5.5.3.5413, Pion Inc.). Blank (100%T), standard, and dissolution spectra were all acquired using FaSSIF as the media at 37 °C with and without 0.05 and 0.1% w/v of predissolved polymers (HPMC, HPMCAS-M, and PVP-VA). Polymers were predissolved in FaSSIF for at least 30 min before etravirine was introduced into the system. Six nonzero calibration standards were made by adding 100 μL of stock solutions of etravirine dissolved in DMSO to 20 mL of FaSSIF media at 37 °C. The concentration of DMSO in the standards and dissolution experiments was 0.5% which is less than the 2% maximum concentration recommended by other authors. , The maximum concentration of the calibration curve (e.g., C ss,100% ) was required to exhibit a raw absorbance signal less than or equal to 1.8 AU, show the same second derivative spectrum shape and zero intercept points in the x -axis as the other standard calibrants, provide linearity with lower standards, and not cause instant etravirine precipitation. In the supersaturation solvent-shift experiments, an aliquot (100 μL) of etravirine stock solution in DMSO was pipetted into 20 mL of FaSSIF media at 37 °C with or without 0.05 and 0.1% predissolved polymers ( n = 6 each condition). Each vial had a stir bar spinning at 100 rpm and a probe submerged by 1 in. The initial concentration in the solvent-shift studies was one of the following: C ss,100% (determined as described above), 87.5% C ss,100% ( C ss,87.5% ), 75% C ss,100% ( C ss,75% ), and 50% C ss,100% ( C ss,50% ). 2.13 Calculation of Supersaturation Indices from Solvent-Shift Studies The supersaturation indices are quantitative approaches to compare the effects of predissolved polymers in the inhibition of etravirine precipitation. , These indices are degree of supersaturation (DS), EGF, and time for 10% of the initial etravirine concentration to precipitate ( T 10% ). DS at time t was calculated as 4 where C ss ( t ) is the drug supersaturated concentration at time t and C eqsol is the drug equilibrium solubility of the crystalline form in the same media. DS was calculated for each time point of the supersaturation studies, and DS versus time profiles were created. EGF was calculated using : 5 where AUC 60min(polymer) is the area under the curve from zero to 60 min of the DS versus time profile in the presence of predissolved polymer and AUC 60min(no polymer) is the area under the curve from zero to 60 min of the DS versus time profile without predissolved polymer. For the supersaturation experiments that finished before 60 min due to full drug precipitation, data were extrapolated to 60 min to calculate DS and EGF.   Overall Study Approach This study focused on expanding the use of 1 HNMR techniques, specifically STD-NMR and T 1 relaxation time, in relation to the drug, to identify polymers that promote drug supersaturation and inhibit crystallization. The overall study approach is shown in . Through STD-NMR and T 1 relaxation time experiments, the etravirine binding strength and etravirine binding epitope with HPMC, HPMCAS-M, and PVP-VA were determined at different drug concentrations. Strong molecular interactions between polymer and etravirine in 1 HNMR were anticipated to reduce the precipitation kinetics in supersaturation studies. Polymers that were expected to promote supersaturation and inhibit etravirine crystallization were identified via 1 HNMR. 1 HNMR results were then challenged through supersaturation studies. The supersaturation studies were conducted by using the solvent-shift methodology. Supersaturation indices such as time to precipitation, degree of supersaturation, and the excipient gain factor (EGF) were calculated.   Materials Etravirine was purchased from ChemShuttle (Burlingame, CA). HPMC (Affinisol HME 15LV) was provided by DuPont (Wilmington, DE). HPMCAS-M (Aquasolve) was gifted by Ashland (Covington, KY). PVP-VA (Kollidon VA 64) was gifted by BASF (Ludwigshafen, Germany). Barnstead GenPure purification system (Thermo Scientific; Waltham, MA) provided purified water. Fasted state simulated intestinal fluid concentrated powder (FaSSIF) was acquired from Biorelevant (London, UK). Sodium phosphate monobasic, sodium hydroxide, sodium chloride, hydrochloric acid, and dimethyl sulfoxide-d6 (DMSO-d6) were acquired from Sigma-Aldrich (St. Louis, MO). Deuterium oxide with 0.03% trimethylsilylpropanoic acid (TSP) was acquired from the Cambridge Isotope Laboratory (Tewksbury, MA). NMR tubes (500 MHz, 5 mm, Standard Series) were acquired from Norell (Morganton, NC).   NMR Sample Preparation and Sample Concentration Solution of etravirine with and without polymers was prepared in 70% DMSO-d6 and 30% D 2 O (0.03% TSP). This solvent proportion was used to ensure total etravirine and polymer solubility. Lower DMSO concentrations were tested but did not solubilize etravirine. The lowest concentration of etravirine that would ensure an appropriate signal-to-noise ratio and reasonable experimental time was approximately 100 μM. 70% DMSO was the lowest concentration of DMSO needed to solubilize etravirine. TSP was used as an internal reference. To better understand the interaction of etravirine and polymer, STD-NMR and T 1 experiments were run with four levels of etravirine concentration. The weight-based (w/w) proportions of etravirine to polymer were 1:1, 2:1, 3:1, and 4:1. The relative abundance of polymer impacts the relative abundance of polymer fragments that may interact with the drug. Etravirine and polymer structures are shown in . Based on the estimated ranges of polymer molecular weight provided by the manufacturers, we used an average molecular weight of 90,000 g/mol for HPMC, 103,200 for HPMCAS-M, and 50,000 g/mol for PVP-VA. The polymer concentrations were fixed at 0.5, 0.6, and 1 uM for HPMCAS, HPMC, and PVP-VA, respectively. shows the specific etravirine and polymer concentrations for each of the four concentration levels in the NMR experiments.   NMR Experiments and Analysis All NMR experiments were performed in a Varian DD2 500 MHz NMR (Agilent, Santa Clara, CA) at 25 °C. Data processing and analysis, as well as spectrum figures, were performed in NMRBox, using OpenVnmrj (Version 2.1A) and MestReNova (Mnova, Version 14.3.1-31739), respectively. Both VNMRJ and Mnova were part of the NMR Box. Etravirine, HPMC, HPMCAS-M, and PVP-VA structures are presented in . Etravirine reportable protons are numbered from 1 through 4.   1 HNMR Peak Assignment Experiments Experiments with etravirine and polymers were performed to assign the proton peaks to specific protons in the etravirine structure and to determine the location of etravirine and polymer proton peaks in the spectrum. Single-pulse proton experiments (vendor-supplied pulse sequence, s2pul, was used) were acquired on etravirine and each of the polymers separately. Spectral width was set to 6009.28 Hz (e.g., 12 ppm, −1 to 11 ppm) and with the transmitter offset at 5 ppm. Relaxation delays of 1.5 s were used. The number of transients acquired was 512. The 90° pulse was set to 7.625 μs at 56 dB. The TSP peak was set to 0 ppm and used as chemical shift reference. HMBC, HMQC, and 13 C NMR were used to assign protons in the etravirine spectrum. The parameters for these experiments are shown in Table S1 .   STD-NMR Experiments The basic STD experiment consisted of a saturation transfer step, delivered by low-power Gaussian-shaped pulses of narrow bandwidth and centered at a selected frequency that alternated between setting followed by a high-power broadband pulse, one on-resonance exclusively at the macromolecule, and one at off-resonance (reference) from all signals. The signals from the on- and off-resonance pathways were stored separately (vendor-supplied pulse sequence of dpfgse-satxfer2). The results from the difference between on- and off-resonance pathways were generated by subtracting the separate fid files. Spectral width was set to 6009.28 Hz (e.g., 12 ppm, −1 to 11 ppm) and with the transmitter offset at 5 ppm. Relaxation delays of 1.5 s were used. The number of transients acquired was 512 and preceded by 4 steady-state acquisitions. The 90° pulse, calibrated for each sample, was typically about 7.625 μs at 56 dB. The TSP peak was set to 0 ppm and used as chemical shift reference. The saturation transfer pulse train consisted of various number of cycles of a 50 ms Gaussian-shaped pulse at −3 dB and a 1 ms interpulse delay, summing up to 0.5, 1, 2, 3, 4, and 5 s of saturation time. The saturation frequency on-resonance with the polymer was set at 3.5 ppm, and the off-resonance was set at 20 ppm. Additional STD-NMR experiments with saturation frequency at 1.7 ppm in samples with PVP-VA were conducted to assess robustness of saturation transfer studies at 3.5 ppm ( Figure S1 ). The STD results using 1.7 and 3.5 ppm were similar. In addition to the experiments with etravirine and polymers, control experiments with only etravirine at concentrations of 237 and 496 μM were conducted to check for the presence of signals in the absence of polymers. The STD-NMR experiments were divided into two parts: on-resonance and off-resonance experiments. During the on-resonance experiments, samples with etravirine and polymer were irradiated with an energy pulse at a selective frequency (3.5 ppm). This frequency corresponded to the protons in the polymer structure. Additionally, this frequency avoided applying energy near etravirine protons, more specifically proton H1 (2.16 ppm). In the off-resonance experiment, the saturation-transfer pulses were away from all signals, from the polymer or drug structure (20 ppm). In the on-resonance experiment, the polymer structure was saturated by selective radio frequency (rf) irradiation. Energy was transferred (i.e., saturation transfer) from the polymer to its surroundings, including, if any, small molecules that were bound specifically to the polymer, through spin diffusion (nuclear Overhauser effect). The STD-NMR signal intensity ( I STD ) was calculated by subtracting the proton peak intensity of the off-resonance spectrum ( I 0 ) by the respective proton peak intensity in the on-resonance spectrum ( I SAT ), as outlined in Viegas et al. . Therefore, only etravirine protons that received the saturation transfer were expected to show an I STD . I STD was an indication of binding between the site of saturation transfer in the polymer to etravirine protons that are within 5 Å to the polymer. , Etravirine protons that were close to the polymer were expected to show higher peak intensities in the difference spectrum (i.e., high I STD ). Protons that did not receive any saturation transfer from the polymer were expected to show the same peak intensities in the on- and off-resonance spectra and show zero I STD . In order to calculate I STD , both on- and off-resonance spectra were recorded on the same vertical scale. 1 The approach to describe the interaction between polymer and drug is to calculate the STD amplification factor ( A STD ) of a given proton in the drug structure. A STD for each of the reportable etravirine protons is calculated by where [ D ] is the drug concentration (i.e., etravirine concentration) and [ P ] is the polymer concentration in moles. 2 A STD represented the magnitude of saturation transfer from the polymer to etravirine. For a specific saturation time, A STD denoted the average number of drug molecules saturated per molecule of polymer. Etravirine protons closer to the polymer were expected to present a higher A STD . In addition, for the drug protons involved in binding, their A STD increased as a function of the saturation time. As saturation time increased, there was a greater turnover of etravirine molecules in the polymer binding site, leading to an increase in I STD signals and consequently an increase in A STD values. Although ASD formulations usually have an excess of polymer by weight in relation to the drug, the STD-NMR in this study followed the methodology applied to screening protein binding ligands. In this methodology, the large molecule (e.g., polymers, proteins) was irradiated with a rf pulse and the energy was transferred to nearby small molecules (e.g., drugs, ligands in general). The small molecule needed to be in excess of the polymer because the energy saturated small molecules (i.e., molecule that received saturation transfer from the big molecule) needed to detach themselves from the large molecule in order to release the energy signal that will be detected by the NMR instrument. STD-NMR was applicable to binding complexes with dissociation constant ( k off ) in the millimolar to micromolar range.   T 1 Relaxation Time Measurements T 1 relaxation time of each proton, also known as the spin–lattice relation time, in the etravirine structure was measured in the absence and presence of polymers. In order to streamline the experiments, the same samples used for STD-NMR experiments were also used for T 1 experiments. Control samples for T 1 experiments did not contain polymers and had the same amount of etravirine as the samples with polymers. The number of scans used in the T 1 experiments was 16. Spectrum width, transmitter offset, number of points in the spectrum, and number of steady-state transients were the same as those for the STD-NMR experiments. T 1 relaxation time was calculated using the inversion recovery method. The time delay [e.g., Tau (τ)] between the inversion pulse and the recovery pulse, as well as the relaxation delay between transients, were optimized based on preliminary T 1 measurements to estimate the shortest and the longest T 1 values. The estimated longest T 1 was used to set the relaxation delay between transients to five to six times the longest T 1 estimate. All T 1 values reported were calculated with a vendor-supplied macro called “ T 1 ” in the OpenVnmrj software. Multiple spectra were collected with different τ values (array of 10–12 τ values), and a nonlinear regression was fitted to obtain T 1 time estimate for each proton using : 3 where M z (τ) is the net magnetization vector along the z -axis at time τ and M 0 is the equilibrium magnetization. After a radio frequency pulse was applied to the protons, the energy traveled from the proton (i.e., spins) to the environment (i.e., lattice), resulting in the return of the spins to the equilibrium state. The T 1 relaxation time was the time that it took for the protons to recover to approximately 63% of their equilibrium magnetization. T 1 relaxation time varied from proton to proton depending on the other atoms in the environment, molecular bonding, solvent, temperature, and other components outside of the molecule that are interacting with the proton. Etravirine protons involved in interacting with the polymers lose energy faster (i.e., small T 1 relaxation time) than do the protons not involved in binding. Therefore, this approach determined which polymers interacted with etravirine molecules. We assumed that specific interactions between etravirine and the polymers provided additional pathways for etravirine protons to dissipate energy and thereby return to equilibrium in a shorter time, as measured by a shorter T 1 . A survey of the T 1 times of the etravirine protons in the absence and presence of polymers was used to identify such energy transfers.   2D- 1 H NOESY Experiments Data from 2D- 1 H NOESY experiments were collected on etravirine in the presence of each of HPMCAS-M and PVP-VA, as well as control samples of each of the polymers by themselves at 25 °C. Etravirine and polymers were at a concentration of 1.5 mg/mL each and in the presence of 70% DMSO/30% D 2 O. Mixing times used ranged from 100 to 500 ms. The total number of points used to record the fids were 2048; spectral width of 12.5 ppm centered at 5.8 ppm was used for both dimensions. A delay between transients of 2 s was used, and 32 transients were acquired per fid. The number of increments acquired in the indirectly detected dimension varied from 200 to 256. The NMR data were processed in NMRPipe (Version 11.5) and viewed in Sparky (Version build_04-22-2021) (NMR Box).   Viscosity of NMR Samples Viscosity measurements were performed with a Discovery HR-2 Rheometer (TA Instruments, New Castle, DE). Samples (300 μL) of etravirine in 70% d6-DMSO/30% D 2 O with and without polymers were analyzed. Samples without the drug and polymer were also analyzed. The concentration of the samples was 4:1 etravirine:polymer, as shown in . Temperature was at a constant temperature of 25 °C and was controlled by a Peltier plate. The bottom plate diameter and cone angle were 40 mm and 1.007°, respectively. The shear rate varied from 1000 to 1400 s –1 . Apparent viscosity was calculated as shear stress over the shear rate.   Preparation of FaSSIF The buffer for FaSSIF preparation was made by dissolving 0.420 g of sodium hydroxide, 3.438 g of sodium phosphate monobasic anhydrous, and 6.186 g of sodium chloride in 0.9 L of purified water. The mix was stirred for 10 min, and then, the pH was adjusted with hydrochloric acid or sodium hydroxide to a pH of 6.5. Additional water was added to make 1 L of the total volume. Buffer was added to 2.240 g of FaSSIF concentrated powder, and the mixture was stirred for 2 h. FaSSIF media was stored at RT and used within 48 h of preparation.   Determining Etravirine Equilibrium Solubility An excess of etravirine was added to 10 mL of FaSSIF that was shaken at 37 °C for 24 h ( n = 6). The media pH was checked, and no change from initial pH conditions was observed. Samples were filtrated with a 0.45 μm PVDF filter, with the first 1 mL being discarded and 1 mL collected for analysis. After filtration, 0.5 mL of sample was evaporated under N 2 at 45 °C. Samples were reconstituted with 100 uL of mobile phase. Samples were analyzed by an isocratic method using 80% methanol and 20% water in a Waters AcquityH Class UPLC system (Waters Corporation; Milford, MA) coupled with a vacuum degasser, quaternary pump, and autosampler. Column used was Poroshell 120 EC-C18 (4 μm, 4.6 mm × 150 mm; Agilent) at 30 °C, flow rate was 1 mL/min, total run time was 4.5 min, and retention time was 3.2 min. The PDA detector was set to a wavelength of 310 nm.   Supersaturation Studies Using Solvent-Shift Methodology and In Situ UV System Etravirine supersaturation studies were conducting using the solvent-shift methodology which was adapted from other publications. , , , , Etravirine concentrations were measured using the Pion μDiss Profiler (Pion, Billerica, MA) coupled with the Pion Rainbow R6 system (Pion Inc.; Billerica, MA) with six probes (2 mm probe size) and analyzed using AuPro Software (ver. 5.5.3.5413, Pion Inc.). Blank (100%T), standard, and dissolution spectra were all acquired using FaSSIF as the media at 37 °C with and without 0.05 and 0.1% w/v of predissolved polymers (HPMC, HPMCAS-M, and PVP-VA). Polymers were predissolved in FaSSIF for at least 30 min before etravirine was introduced into the system. Six nonzero calibration standards were made by adding 100 μL of stock solutions of etravirine dissolved in DMSO to 20 mL of FaSSIF media at 37 °C. The concentration of DMSO in the standards and dissolution experiments was 0.5% which is less than the 2% maximum concentration recommended by other authors. , The maximum concentration of the calibration curve (e.g., C ss,100% ) was required to exhibit a raw absorbance signal less than or equal to 1.8 AU, show the same second derivative spectrum shape and zero intercept points in the x -axis as the other standard calibrants, provide linearity with lower standards, and not cause instant etravirine precipitation. In the supersaturation solvent-shift experiments, an aliquot (100 μL) of etravirine stock solution in DMSO was pipetted into 20 mL of FaSSIF media at 37 °C with or without 0.05 and 0.1% predissolved polymers ( n = 6 each condition). Each vial had a stir bar spinning at 100 rpm and a probe submerged by 1 in. The initial concentration in the solvent-shift studies was one of the following: C ss,100% (determined as described above), 87.5% C ss,100% ( C ss,87.5% ), 75% C ss,100% ( C ss,75% ), and 50% C ss,100% ( C ss,50% ).   Calculation of Supersaturation Indices from Solvent-Shift Studies The supersaturation indices are quantitative approaches to compare the effects of predissolved polymers in the inhibition of etravirine precipitation. , These indices are degree of supersaturation (DS), EGF, and time for 10% of the initial etravirine concentration to precipitate ( T 10% ). DS at time t was calculated as 4 where C ss ( t ) is the drug supersaturated concentration at time t and C eqsol is the drug equilibrium solubility of the crystalline form in the same media. DS was calculated for each time point of the supersaturation studies, and DS versus time profiles were created. EGF was calculated using : 5 where AUC 60min(polymer) is the area under the curve from zero to 60 min of the DS versus time profile in the presence of predissolved polymer and AUC 60min(no polymer) is the area under the curve from zero to 60 min of the DS versus time profile without predissolved polymer. For the supersaturation experiments that finished before 60 min due to full drug precipitation, data were extrapolated to 60 min to calculate DS and EGF.   Results and Discussion 3.1 1 HNMR The single-pulse 1 HNMR spectra of etravirine control samples (i.e., without polymers), and in the presence of HPMC, HPMCAS-M, and PVP-VA, are shown in . All the nonexchangeable protons of etravirine were assigned, based on the proton, carbon, as well as 2D experiments HMQC and HMBC (data not shown). The protons in ring A are H1 (2.162, singlet, 6 protons) and H4 (7.749 ppm, singlet, 2 protons); the protons in ring C are H2 (7.397, doublet, 2 protons) and H3 (7.429, doublet, 2 protons). These protons are highlighted in the etravirine structure in . These peaks are referred to as reportable protons in the etravirine structure because they consistently appear in the single-pulse 1 HNMR, T 1 , and STD-NMR spectra that do not overlap with the polymer peaks, except proton H1 slightly overlapped with PVP-VA. The protons in ring B exchange rapidly with the water in the sample and do not appear as peaks distinct from the water peak; thus, the contribution of the amine/aniline protons cannot be directly assessed. However, ring B binding interaction effects can be gleaned from their neighboring protons. In , proton polymer peaks were not assigned to a specific region in the polymer structure. 3.2 STD-NMR Control Experiments Etravirine samples without polymer were saturated with rf pulses for 0.5–5 s at 3.5 and 20 ppm, in and on- and off-resonance experiments, respectively. Peaks corresponding to H1 were present at very low intensities in the difference spectra of these control experiments, perhaps due to slight instabilities in the instrument. However, the intensity of these peaks did not increase with saturation time as were observed for samples of etravirine in the presence of polymers . 3.3 STD-NMR Experiments with Polymers shows the A STD for etravirine protons in the presence of HPMC, HPMCAS-M, and PVP-VA at four concentration ratios as shown in . Overall, etravirine showed a higher molecular interaction with HPMCAS-M followed by HPMC, as shown by the A STD values across the saturation times. Minimal interaction was observed in the presence of PVP-VA, as shown by the small A STD values observed across saturation times. A steady increase in A STD values for all protons was observed as the saturation times increased until they reached a plateau for all concentration levels. These findings were expected as the I STD signal tended to show a buildup region, where the signal increases, and a plateau region, where the signal reaches a plateau. These regions were easily identifiable for all protons in the presence of HPMC and HPMCAS-M. At the two lower concentrations of etravirine, binding to HPMC was as strong as or even slightly higher than that of HPMCAS-M. However, A STD values in the presence of HPMC did not change substantially as etravirine concentration increased. The etravirine protons A STD were higher in the presence HPMCAS-M for most concentration levels. Protons A STD at approximately 240 μM were higher for HPMC, but not much different than their A STD in the presence of HPMCAS-M. For all protons in the presence of HPMCAS-M, an increase in etravirine concentration and saturation time led to an increase in A STD . There was very little saturation transfer from PVP-VA to etravirine, as indicated by the small A STD values across all four etravirine concentration levels and saturation times. These findings indicate that etravirine interacted preferably to HPMCAS-M, HPMC, and PVP-VA, in this order. The intensity of proton A STD values depended on the saturation time (i.e., for how long the rf pulse was applied to the polymer), number of etravirine molecules to polymer molecules in the sample, etravirine dissociation rate constant, and polymer tumbling rate. The STD-NMR experiments here varied the number of excess etravirine molecules to polymer molecules and saturation time to obtain an efficient interaction of etravirine with polymers. An increase in A STD as saturation time increased was expected since longer saturation times allowed for the transfer of energy from the polymer to more etravirine molecules. An increase in excess of etravirine molecules to polymer molecules also increased A STD signals, since more etravirine molecules interacted with the polymer. STD-NMR experiments were conducted with four etravirine concentration levels, which are shown in , and using six saturation times (0.5, 1, 2, 3, 4, and 5 s). There are two possible conclusions to the lack of A STD values for all etravirine protons in the presence of PVP-VA. First, there was no or minimal saturation transfer from PVP-VA to etravirine because they minimally interacted (i.e., etravirine molecules are further than 5 Å from PVP-VA molecules). A second possible conclusion is that PVP-VA and etravirine molecules interacted, but the interaction was too strong, and etravirine did not dissociate from the interaction with PVP-VA. If etravirine is a high affinity ligand for PVP-VA, then the etravirine molecules cannot efficiently release the transferred energy to the solution that can be detected by the spectrometer. Overall, the STD-NMR experiments showed a preferable interaction between etravirine and HPMCAS-M and HPMC, in this order. PVP-VA showed small values of A STD which could indicate minimal interaction or a high affinity of etravirine for this polymer. Overall, from STD-NMR results, HPMCAS-M and HPMC would be more successful than PVP-VA in promoting drug supersaturation and preventing drug precipitation in solvent-shift studies. 3.4 T 1 Relaxation Time Experiments Etravirine protons’ T 1 relaxation times were measured in the absence and presence of HPMC, HPMCAS-M, and PVP-VA. Each proton in the etravirine structure exhibited a different T 1 time, and the T 1 time was affected by what is surrounding the proton. The concentrations of etravirine and the polymer are shown in . To better understand the effects of the polymers on the etravirine T 1 relaxation time, the percentage change in T 1 time from the control samples (i.e., samples without polymer) was evaluated. shows the percentage change in T 1 times for protons H1–H4 at four ratios of etravirine to polymer. The T 1 relaxation time values for each proton under all conditions studied are shown in Tables S2–S4 . The T 1 relaxation time of the exocyclic methyl groups in ring A (e.g., H1) was the least affected by the addition of polymers to the sample, as these protons showed small increases (i.e., approximately <5% change) in T 1 time across all ratios of etravirine to polymers. On the other hand, the aromatic protons in ring A (e.g., H4), as well as aromatic protons in rings C (e.g., H2 and H3), showed substantial decrease in their T 1 times in the presence of HPMC and HPMCAS-M (i.e., approximately range from 5 to 20% change) across the four etravirine:polymer ratios. In contrast, these protons showed small changes in the presence of PVP-VA (i.e., approximately <5% change) across all four ratios. There was no trend in the change in T 1 times as a function of the etravirine concentration. The mechanism behind the T 1 relaxation time involves the energy exchange from the etravirine protons with the surrounding environment (i.e., the lattice). The components in the environment that affected T 1 times were the presence of other atoms within and around the etravirine molecule. Etravirine self-aggregation was not considered as a source of change in T 1 times in this study, as there was no trend in the change in T 1 times as a function of the etravirine concentration in the control samples. There are two possible mechanisms for T 1 time change in the presence of HPMC and HPMCAS-M. The polymers could be increasing the viscosity of the sample, which would lead to a decrease in the T 1 times as the etravirine molecules would tumble less. , In addition, molecular interactions between etravirine and HPMC and HPMCAS-M could be the reason for a decrease in proton T 1 times, as the etravirine protons would lose energy to nearby polymer molecules. Etravirine proton low A STD values observed in the presence of PVP-VA from STD-NMR experiments pointed to two possible hypotheses. One hypothesis is that etravirine bound very tightly to PVP-VA (e.g., k off = 0.1–0.01 s –1 ) and no drugs dissociated from the polymer binding site, and no to little signal was shown in the STD-NMR experiments. The second hypothesis was that there was little or no binding interaction between drug and PVP-VA. T 1 relaxation time results provided more insights into the characteristics of possible etravirine and PVP-VA interactions. Etravirine protons did not show any meaningful changes in T 1 times in the presence of PVP-VA. If binding occurred, a decrease in etravirine proton T 1 times was expected. Therefore, combined results from STD-NMR and T 1 relaxation times indicated no molecular interaction between etravirine and PVP-VA. 3.5 2D- 1 H NOESY Plots of etravirine and HPMCAS-M and PVP-VA are shown in Figure S2 . In Panel S2 , etravirine protons H1–H4 interactions with HPMCAS-M are shown as cross-peaks in the red rectangles around 2 and 7 ppm. In Figure S2 Panel B, PVP-VA cross-peaks are present (blue rectangle), showing that there is magnetization transfer. However, no interaction was observed between etravirine protons and PVP-VA. Both 2D- 1 H NOESY results corroborate the findings of STD-NMR and T 1 relaxation time, showing that etravirine interacts preferably to HPMCAS-M than PVP-VA. 3.6 NMR Sample Viscosity NMR findings were not impacted by sample viscosity, where samples contained different polymers. Samples behaved as a Newtonian fluid with a constant viscosity across shear rates. The viscosities of samples without polymer (and with or without drug) were 0.00439 ± 0.00002 Pa.s. Viscosity of the drug sample with HPMC, HPMCAS-M, or PVP-VA was 0.00445 ± 0.00002, 0.00449 ± 0.00004, and 0.00480 ± 0.00004 Pa.s, respectively. Overall, polymer (or drug) did not impact viscosity, where viscosity can generally vary over several orders of magnitude. At best, PVP-VA minimally raised viscosity, but etravirine T 1 time did not change in the presence of PVP-VA, reflecting that viscosity was not a factor in NMR findings. 3.7 Etravirine Equilibrium Solubility Etravirine equilibrium solubility was 0.52 ± 0.11 μg/mL in FaSSIF. Other researchers have found etravirine solubility to be about 0.99 μg/mL in FaSSIF. 3.8 Supersaturation Studies Using Solvent-Shift Methodology and In Situ UV System A linear calibration curve of etravirine was created for each probe in each of the supersaturation conditions (i.e., no polymer, 0.05% predissolved polymer, and 0.1% predissolved polymer). All acceptable etravirine standards had a UV spectrum that crossed the x -axis in the second derivative at the same points of interception. Etravirine concentration calculation employed a wavelength range of 286–296 in the second derivative. The maximum concentration for the solvent-shift studies ( C ss,100% ), in addition to the other concentration levels ( C ss,87.5% , C ss,75% , and C ss,50% ) for each experimental condition, is presented in . Initial concentrations were determined as the highest concentration in the linear calibration curve that did not cause immediate precipitation. There were no major differences in the initial concentrations used. Supersaturation experiments were carried out for 120 min or less. Experiments were stopped before 120 min if most of the drug precipitation transpired per UV spectrum. Precipitation was determined as a shift in the shape of the spectrum in the second derivative. An example of the etravirine spectrum over time during the experiment is shown in Figure S3 . Supersaturation studies without predissolved polymer showed that etravirine precipitated within 3 min at concentrations of C ss,100% , C ss,87.5% , and C ss,75% . Precipitation was steep with these higher concentrations than with the C ss,50% concentration. Etravirine took longer to precipitate from the C ss,50% concentration and reached the precipitation plateau after approximately 30 min, as shown in . The presence of predissolved 0.05 and 0.1% polymers in the FaSSIF media delayed etravirine precipitation at C ss,100% , C ss,87.5% , C ss,75% , and C ss,50% concentrations, as shown in . HPMC and HPMCAS-M at 0.05 and 0.1% concentrations not only delayed the start of etravirine precipitation from its supersaturated concentration but also decreased the rate of precipitation. Complete drug precipitation was not observed in the presence of these polymers within 120 min. Despite promoting supersaturation and inhibiting precipitation when compared to no polymer present, PVP-VA at concentrations of 0.05 and 0.1% only delayed precipitation until around 20 min. Overall, HPMC and HPMCAS-M outperformed PVP-VA in maintaining drug in supersaturated solution for a longer time. 3.9 Calculation of Supersaturation Indices from Supersaturation Studies Supersaturation indices were calculated to further characterize the capacities of three polymers for sustaining supersaturation and preventing crystallization. DS was calculated for each time point in the supersaturation concentration versus time profiles, as shown in and . The DS versus time profiles without and with predissolved polymers are shown in Figures S4 and S5 , respectively. Etravirine equilibrium solubility here was found to be 0.52 μg/mL in FaSSIF with no predissolved polymer. Figures S4 and S5 showing the DS versus time profiles indicate that all polymers here were able to keep at least 50 times more etravirine dissolved in solution compared with the drug equilibrium solubility in FaSSIF. Additionally, polymer EGF was calculated as the ratio of AUC 60 min in the presence and absence of predissolved polymer. AUC 60 min was the area under the curve of the DS versus time profiles from 0 to 60 min. Polymer EGF for each experimental condition is shown in . HPMCAS-M and HPMC at concentrations of 0.1% showed the greatest EGF, followed by 0.05% HPMCAS-M and HPMC. HPMCAS-M slightly outperformed HPMC at both polymer concentrations and at all four etravirine concentrations. Regardless of PVP-VA concentration, this polymer underperformed by almost half, as shown by its EGF compared to HPMC and HPMCAS-M across all four levels of etravirine concentration in . shows the impact of polymer on time for 10% of the initial etravirine supersaturated concentration to precipitate ( T –10% ). T –10% was selected as a measure of the early precipitation. Etravirine started to precipitate within 1 min with no predissolved polymer in the media. Polymers were predissolved at concentrations of 0.05 and 0.1%. With the addition of predissolved 0.05% HPMC, T –10% increased to over 30 min across the four etravirine initial concentrations. 0.1% HPMC delayed T –10% only at the etravirine concentrations of C ss75% and C ss50% . Like HPMC, 0.05% HPMCAS-M also increased T –10% by over 30 min across all four initial concentrations. However, T –10% increased to over 50 min consistently across initial concentrations with 0.1% HPMCAS-M. Meanwhile, both concentrations of PVP-VA did not increase T –10% above 20 min for any of the four initial supersaturated concentrations of etravirine. Therefore, like EGF, T –10% showed that 0.1% HPMCAS-M was the most successful polymer in maintaining supersaturation and inhibiting drug precipitation, followed by 0.1% HPMC. 3.10 Implications of 1 HNMR and Supersaturation Study Results The combined results from the STD-NMR and T 1 relaxation time indicate etravirine bound preferably to HPMCAS-M > HPMC ≫ PVP-VA ( and ). Binding affinity was largest for HPMCAS-M, where A STD values increased with a larger etravirine concentration . The binding affinity rank order was corroborated by the T 1 relaxation time results. Etravirine protons H2, H3, and H4 showed a decrease in the T 1 times in the presence of HPMC and HPCMAS-M . While T 1 identified PVP-VA interacted minimally with etravirine, T 1 indicated that HPMC and HPMCAS-M each bound with etravirine but could not differentiate their qualitative strengths in binding, unlike STD-NMR. Nevertheless, the results of both STD-NMR and T 1 relaxation time point to a preferable binding affinity to HPMCAS-M and HPMC over PVP-VA. Of note, the low A STD values of PVP-VA from STD-NMR pointed to either very low binding affinity or very high binding affinity , but T 1 time clarified that binding affinity was very low. The results from 2D- 1 H NOESY corroborated STD-NMR and T1 relaxation time results, showing that etravirine interacts more preferably with HPMCAS-M than with PVP-VA. Etravirine proton cross-peaks showed the drug interacted with HPMCAS-M. Meanwhile, no interaction was observed between etravirine protons and PVP-VA protons, despite the presence of magnetization transfer among the PVP-VA protons ( Figure S2 ). Both 2D- 1 H NOESY results corroborate the findings of STD-NMR and T1 relaxation time, showing that etravirine interacts more preferably to HPMCAS-M than PVP-VA. STD-NMR and T 1 relaxation time yielded insight into what portions of etravirine structure bound with HPMCAS-M and HPMC. In the presence of HPMC and HPMCAS-M, etravirine protons H4 in ring A and protons H2 and H3 in ring C showed higher A STD values across all saturation times than proton H1 in ring A, indicating that these protons are closer to the polymer site of saturation transfer and receive more efficient saturation transfer. T 1 relaxation time results agreed with these STD-NMR results, as the protons H4 in ring A and H2 and H3 in ring C showed a decrease in T 1 times in the presence of HPMCAS-M and HPMC. The aliphatic protons H1 in ring A provided the smallest A STD signals, albeit still present, and correspondingly did not show a consistent decrease in T 1 time. Therefore, proton H4 in ring A and protons H2 and H3 in ring C contribute to binding to each HPMC and HPMCAS-M. In addition, STD-NMR and T 1 relaxation time experiments were sensitive methods that were able to identify the differences within the same moiety (e.g., ring A) and its neighbors (e.g., ring C), with specificity at the atomic level. The strong hydrophobic interactions between etravirine and polymers HPMCAS-M and HPMC observed by STD-NMR and T 1 relaxation time indicated that HPMCAS-M and HPMC are suitable polymers to maintain etravirine supersaturation and inhibit drug precipitation. Supersaturation studies using solvent-shift technique corroborated our hypothesis as predissolved HPMCAS-M and HPMC, but not PVP-VA, markedly promoted etravirine supersaturation and inhibited drug precipitation. The supersaturation index EGF showed that each 0.1% HMCAS-M and 0.1% HPMC outperformed PVP-VA, by almost 2-fold, to maintain etravirine in solution (i.e., HPMCAS-M EGF = 5.2, HPMC EGF = 5.0, while PVP-VA EGF = 3.1). HPMCAS-M delayed T –10% by almost twice the time compared to HPMC, which in turn delayed T –10% by over 5-fold when compared to PVP-VA, at both concentrations of predissolved polymers. The addition of more PVP-VA (e.g., 0.05% vs 0.1%) did not improve the performance of this polymer, unlike HPMC and HPMCAS-M, where additional polymer further reduced the T –10% time. The hypothesized mechanism for the performance of HPMCAS-M and HPMC in promoting drug supersaturation and preventing drug crystallization is decreased etravirine motility and suppression of etravirine nucleation and precipitation. Previous studies have shown agreement between strong intermolecular interactions observed through NMR and the inhibition of drug precipitation. For example, HPMCAS-H suppressed carbamazepine molecular motility and suppressed precipitation, via strong drug–polymer interactions. In addition, molecular interactions between poly(acrylic acid) and ketoconazole reduced molecular mobility and prevented crystallization in liquid state NMR and dissolution experiments. In contrast, other studies involving a weakly basic and an anionic polymer showed strong interactions to be a relative detriment. For example, interactions between HPMCAS-H grade and itraconazole not only promoted retardation of drug precipitation but also notably promoted higher stabilization of itraconazole that limited drug dissolution/permeation. In addition, ionic interactions, such as between loratadine and HPMCAS-M, can result in poor drug release. The NMR experiments here did not aim to mimic gastrointestinal physiology; instead, the NMR experimental approaches described here are a screening tool and are used to streamline polymer selection to sustain drug supersaturation for further in vitro studies. Etravirine is formulated with HPMC in tablet product Intelence. The results here show that this polymer has strong molecular interactions in HNMR experiments and successfully maintained etravirine in solution in supersaturation studies. HPMCAS-M outperformed HPMC here and, although more recently introduced as a commercial excipient, appears here as an alternative, viable polymer to HPMC to fabricate an etravirine ASD.   1 HNMR The single-pulse 1 HNMR spectra of etravirine control samples (i.e., without polymers), and in the presence of HPMC, HPMCAS-M, and PVP-VA, are shown in . All the nonexchangeable protons of etravirine were assigned, based on the proton, carbon, as well as 2D experiments HMQC and HMBC (data not shown). The protons in ring A are H1 (2.162, singlet, 6 protons) and H4 (7.749 ppm, singlet, 2 protons); the protons in ring C are H2 (7.397, doublet, 2 protons) and H3 (7.429, doublet, 2 protons). These protons are highlighted in the etravirine structure in . These peaks are referred to as reportable protons in the etravirine structure because they consistently appear in the single-pulse 1 HNMR, T 1 , and STD-NMR spectra that do not overlap with the polymer peaks, except proton H1 slightly overlapped with PVP-VA. The protons in ring B exchange rapidly with the water in the sample and do not appear as peaks distinct from the water peak; thus, the contribution of the amine/aniline protons cannot be directly assessed. However, ring B binding interaction effects can be gleaned from their neighboring protons. In , proton polymer peaks were not assigned to a specific region in the polymer structure.   STD-NMR Control Experiments Etravirine samples without polymer were saturated with rf pulses for 0.5–5 s at 3.5 and 20 ppm, in and on- and off-resonance experiments, respectively. Peaks corresponding to H1 were present at very low intensities in the difference spectra of these control experiments, perhaps due to slight instabilities in the instrument. However, the intensity of these peaks did not increase with saturation time as were observed for samples of etravirine in the presence of polymers .   STD-NMR Experiments with Polymers shows the A STD for etravirine protons in the presence of HPMC, HPMCAS-M, and PVP-VA at four concentration ratios as shown in . Overall, etravirine showed a higher molecular interaction with HPMCAS-M followed by HPMC, as shown by the A STD values across the saturation times. Minimal interaction was observed in the presence of PVP-VA, as shown by the small A STD values observed across saturation times. A steady increase in A STD values for all protons was observed as the saturation times increased until they reached a plateau for all concentration levels. These findings were expected as the I STD signal tended to show a buildup region, where the signal increases, and a plateau region, where the signal reaches a plateau. These regions were easily identifiable for all protons in the presence of HPMC and HPMCAS-M. At the two lower concentrations of etravirine, binding to HPMC was as strong as or even slightly higher than that of HPMCAS-M. However, A STD values in the presence of HPMC did not change substantially as etravirine concentration increased. The etravirine protons A STD were higher in the presence HPMCAS-M for most concentration levels. Protons A STD at approximately 240 μM were higher for HPMC, but not much different than their A STD in the presence of HPMCAS-M. For all protons in the presence of HPMCAS-M, an increase in etravirine concentration and saturation time led to an increase in A STD . There was very little saturation transfer from PVP-VA to etravirine, as indicated by the small A STD values across all four etravirine concentration levels and saturation times. These findings indicate that etravirine interacted preferably to HPMCAS-M, HPMC, and PVP-VA, in this order. The intensity of proton A STD values depended on the saturation time (i.e., for how long the rf pulse was applied to the polymer), number of etravirine molecules to polymer molecules in the sample, etravirine dissociation rate constant, and polymer tumbling rate. The STD-NMR experiments here varied the number of excess etravirine molecules to polymer molecules and saturation time to obtain an efficient interaction of etravirine with polymers. An increase in A STD as saturation time increased was expected since longer saturation times allowed for the transfer of energy from the polymer to more etravirine molecules. An increase in excess of etravirine molecules to polymer molecules also increased A STD signals, since more etravirine molecules interacted with the polymer. STD-NMR experiments were conducted with four etravirine concentration levels, which are shown in , and using six saturation times (0.5, 1, 2, 3, 4, and 5 s). There are two possible conclusions to the lack of A STD values for all etravirine protons in the presence of PVP-VA. First, there was no or minimal saturation transfer from PVP-VA to etravirine because they minimally interacted (i.e., etravirine molecules are further than 5 Å from PVP-VA molecules). A second possible conclusion is that PVP-VA and etravirine molecules interacted, but the interaction was too strong, and etravirine did not dissociate from the interaction with PVP-VA. If etravirine is a high affinity ligand for PVP-VA, then the etravirine molecules cannot efficiently release the transferred energy to the solution that can be detected by the spectrometer. Overall, the STD-NMR experiments showed a preferable interaction between etravirine and HPMCAS-M and HPMC, in this order. PVP-VA showed small values of A STD which could indicate minimal interaction or a high affinity of etravirine for this polymer. Overall, from STD-NMR results, HPMCAS-M and HPMC would be more successful than PVP-VA in promoting drug supersaturation and preventing drug precipitation in solvent-shift studies.   T 1 Relaxation Time Experiments Etravirine protons’ T 1 relaxation times were measured in the absence and presence of HPMC, HPMCAS-M, and PVP-VA. Each proton in the etravirine structure exhibited a different T 1 time, and the T 1 time was affected by what is surrounding the proton. The concentrations of etravirine and the polymer are shown in . To better understand the effects of the polymers on the etravirine T 1 relaxation time, the percentage change in T 1 time from the control samples (i.e., samples without polymer) was evaluated. shows the percentage change in T 1 times for protons H1–H4 at four ratios of etravirine to polymer. The T 1 relaxation time values for each proton under all conditions studied are shown in Tables S2–S4 . The T 1 relaxation time of the exocyclic methyl groups in ring A (e.g., H1) was the least affected by the addition of polymers to the sample, as these protons showed small increases (i.e., approximately <5% change) in T 1 time across all ratios of etravirine to polymers. On the other hand, the aromatic protons in ring A (e.g., H4), as well as aromatic protons in rings C (e.g., H2 and H3), showed substantial decrease in their T 1 times in the presence of HPMC and HPMCAS-M (i.e., approximately range from 5 to 20% change) across the four etravirine:polymer ratios. In contrast, these protons showed small changes in the presence of PVP-VA (i.e., approximately <5% change) across all four ratios. There was no trend in the change in T 1 times as a function of the etravirine concentration. The mechanism behind the T 1 relaxation time involves the energy exchange from the etravirine protons with the surrounding environment (i.e., the lattice). The components in the environment that affected T 1 times were the presence of other atoms within and around the etravirine molecule. Etravirine self-aggregation was not considered as a source of change in T 1 times in this study, as there was no trend in the change in T 1 times as a function of the etravirine concentration in the control samples. There are two possible mechanisms for T 1 time change in the presence of HPMC and HPMCAS-M. The polymers could be increasing the viscosity of the sample, which would lead to a decrease in the T 1 times as the etravirine molecules would tumble less. , In addition, molecular interactions between etravirine and HPMC and HPMCAS-M could be the reason for a decrease in proton T 1 times, as the etravirine protons would lose energy to nearby polymer molecules. Etravirine proton low A STD values observed in the presence of PVP-VA from STD-NMR experiments pointed to two possible hypotheses. One hypothesis is that etravirine bound very tightly to PVP-VA (e.g., k off = 0.1–0.01 s –1 ) and no drugs dissociated from the polymer binding site, and no to little signal was shown in the STD-NMR experiments. The second hypothesis was that there was little or no binding interaction between drug and PVP-VA. T 1 relaxation time results provided more insights into the characteristics of possible etravirine and PVP-VA interactions. Etravirine protons did not show any meaningful changes in T 1 times in the presence of PVP-VA. If binding occurred, a decrease in etravirine proton T 1 times was expected. Therefore, combined results from STD-NMR and T 1 relaxation times indicated no molecular interaction between etravirine and PVP-VA.   2D- 1 H NOESY Plots of etravirine and HPMCAS-M and PVP-VA are shown in Figure S2 . In Panel S2 , etravirine protons H1–H4 interactions with HPMCAS-M are shown as cross-peaks in the red rectangles around 2 and 7 ppm. In Figure S2 Panel B, PVP-VA cross-peaks are present (blue rectangle), showing that there is magnetization transfer. However, no interaction was observed between etravirine protons and PVP-VA. Both 2D- 1 H NOESY results corroborate the findings of STD-NMR and T 1 relaxation time, showing that etravirine interacts preferably to HPMCAS-M than PVP-VA.   NMR Sample Viscosity NMR findings were not impacted by sample viscosity, where samples contained different polymers. Samples behaved as a Newtonian fluid with a constant viscosity across shear rates. The viscosities of samples without polymer (and with or without drug) were 0.00439 ± 0.00002 Pa.s. Viscosity of the drug sample with HPMC, HPMCAS-M, or PVP-VA was 0.00445 ± 0.00002, 0.00449 ± 0.00004, and 0.00480 ± 0.00004 Pa.s, respectively. Overall, polymer (or drug) did not impact viscosity, where viscosity can generally vary over several orders of magnitude. At best, PVP-VA minimally raised viscosity, but etravirine T 1 time did not change in the presence of PVP-VA, reflecting that viscosity was not a factor in NMR findings.   Etravirine Equilibrium Solubility Etravirine equilibrium solubility was 0.52 ± 0.11 μg/mL in FaSSIF. Other researchers have found etravirine solubility to be about 0.99 μg/mL in FaSSIF.   Supersaturation Studies Using Solvent-Shift Methodology and In Situ UV System A linear calibration curve of etravirine was created for each probe in each of the supersaturation conditions (i.e., no polymer, 0.05% predissolved polymer, and 0.1% predissolved polymer). All acceptable etravirine standards had a UV spectrum that crossed the x -axis in the second derivative at the same points of interception. Etravirine concentration calculation employed a wavelength range of 286–296 in the second derivative. The maximum concentration for the solvent-shift studies ( C ss,100% ), in addition to the other concentration levels ( C ss,87.5% , C ss,75% , and C ss,50% ) for each experimental condition, is presented in . Initial concentrations were determined as the highest concentration in the linear calibration curve that did not cause immediate precipitation. There were no major differences in the initial concentrations used. Supersaturation experiments were carried out for 120 min or less. Experiments were stopped before 120 min if most of the drug precipitation transpired per UV spectrum. Precipitation was determined as a shift in the shape of the spectrum in the second derivative. An example of the etravirine spectrum over time during the experiment is shown in Figure S3 . Supersaturation studies without predissolved polymer showed that etravirine precipitated within 3 min at concentrations of C ss,100% , C ss,87.5% , and C ss,75% . Precipitation was steep with these higher concentrations than with the C ss,50% concentration. Etravirine took longer to precipitate from the C ss,50% concentration and reached the precipitation plateau after approximately 30 min, as shown in . The presence of predissolved 0.05 and 0.1% polymers in the FaSSIF media delayed etravirine precipitation at C ss,100% , C ss,87.5% , C ss,75% , and C ss,50% concentrations, as shown in . HPMC and HPMCAS-M at 0.05 and 0.1% concentrations not only delayed the start of etravirine precipitation from its supersaturated concentration but also decreased the rate of precipitation. Complete drug precipitation was not observed in the presence of these polymers within 120 min. Despite promoting supersaturation and inhibiting precipitation when compared to no polymer present, PVP-VA at concentrations of 0.05 and 0.1% only delayed precipitation until around 20 min. Overall, HPMC and HPMCAS-M outperformed PVP-VA in maintaining drug in supersaturated solution for a longer time.   Calculation of Supersaturation Indices from Supersaturation Studies Supersaturation indices were calculated to further characterize the capacities of three polymers for sustaining supersaturation and preventing crystallization. DS was calculated for each time point in the supersaturation concentration versus time profiles, as shown in and . The DS versus time profiles without and with predissolved polymers are shown in Figures S4 and S5 , respectively. Etravirine equilibrium solubility here was found to be 0.52 μg/mL in FaSSIF with no predissolved polymer. Figures S4 and S5 showing the DS versus time profiles indicate that all polymers here were able to keep at least 50 times more etravirine dissolved in solution compared with the drug equilibrium solubility in FaSSIF. Additionally, polymer EGF was calculated as the ratio of AUC 60 min in the presence and absence of predissolved polymer. AUC 60 min was the area under the curve of the DS versus time profiles from 0 to 60 min. Polymer EGF for each experimental condition is shown in . HPMCAS-M and HPMC at concentrations of 0.1% showed the greatest EGF, followed by 0.05% HPMCAS-M and HPMC. HPMCAS-M slightly outperformed HPMC at both polymer concentrations and at all four etravirine concentrations. Regardless of PVP-VA concentration, this polymer underperformed by almost half, as shown by its EGF compared to HPMC and HPMCAS-M across all four levels of etravirine concentration in . shows the impact of polymer on time for 10% of the initial etravirine supersaturated concentration to precipitate ( T –10% ). T –10% was selected as a measure of the early precipitation. Etravirine started to precipitate within 1 min with no predissolved polymer in the media. Polymers were predissolved at concentrations of 0.05 and 0.1%. With the addition of predissolved 0.05% HPMC, T –10% increased to over 30 min across the four etravirine initial concentrations. 0.1% HPMC delayed T –10% only at the etravirine concentrations of C ss75% and C ss50% . Like HPMC, 0.05% HPMCAS-M also increased T –10% by over 30 min across all four initial concentrations. However, T –10% increased to over 50 min consistently across initial concentrations with 0.1% HPMCAS-M. Meanwhile, both concentrations of PVP-VA did not increase T –10% above 20 min for any of the four initial supersaturated concentrations of etravirine. Therefore, like EGF, T –10% showed that 0.1% HPMCAS-M was the most successful polymer in maintaining supersaturation and inhibiting drug precipitation, followed by 0.1% HPMC.   Implications of 1 HNMR and Supersaturation Study Results The combined results from the STD-NMR and T 1 relaxation time indicate etravirine bound preferably to HPMCAS-M > HPMC ≫ PVP-VA ( and ). Binding affinity was largest for HPMCAS-M, where A STD values increased with a larger etravirine concentration . The binding affinity rank order was corroborated by the T 1 relaxation time results. Etravirine protons H2, H3, and H4 showed a decrease in the T 1 times in the presence of HPMC and HPCMAS-M . While T 1 identified PVP-VA interacted minimally with etravirine, T 1 indicated that HPMC and HPMCAS-M each bound with etravirine but could not differentiate their qualitative strengths in binding, unlike STD-NMR. Nevertheless, the results of both STD-NMR and T 1 relaxation time point to a preferable binding affinity to HPMCAS-M and HPMC over PVP-VA. Of note, the low A STD values of PVP-VA from STD-NMR pointed to either very low binding affinity or very high binding affinity , but T 1 time clarified that binding affinity was very low. The results from 2D- 1 H NOESY corroborated STD-NMR and T1 relaxation time results, showing that etravirine interacts more preferably with HPMCAS-M than with PVP-VA. Etravirine proton cross-peaks showed the drug interacted with HPMCAS-M. Meanwhile, no interaction was observed between etravirine protons and PVP-VA protons, despite the presence of magnetization transfer among the PVP-VA protons ( Figure S2 ). Both 2D- 1 H NOESY results corroborate the findings of STD-NMR and T1 relaxation time, showing that etravirine interacts more preferably to HPMCAS-M than PVP-VA. STD-NMR and T 1 relaxation time yielded insight into what portions of etravirine structure bound with HPMCAS-M and HPMC. In the presence of HPMC and HPMCAS-M, etravirine protons H4 in ring A and protons H2 and H3 in ring C showed higher A STD values across all saturation times than proton H1 in ring A, indicating that these protons are closer to the polymer site of saturation transfer and receive more efficient saturation transfer. T 1 relaxation time results agreed with these STD-NMR results, as the protons H4 in ring A and H2 and H3 in ring C showed a decrease in T 1 times in the presence of HPMCAS-M and HPMC. The aliphatic protons H1 in ring A provided the smallest A STD signals, albeit still present, and correspondingly did not show a consistent decrease in T 1 time. Therefore, proton H4 in ring A and protons H2 and H3 in ring C contribute to binding to each HPMC and HPMCAS-M. In addition, STD-NMR and T 1 relaxation time experiments were sensitive methods that were able to identify the differences within the same moiety (e.g., ring A) and its neighbors (e.g., ring C), with specificity at the atomic level. The strong hydrophobic interactions between etravirine and polymers HPMCAS-M and HPMC observed by STD-NMR and T 1 relaxation time indicated that HPMCAS-M and HPMC are suitable polymers to maintain etravirine supersaturation and inhibit drug precipitation. Supersaturation studies using solvent-shift technique corroborated our hypothesis as predissolved HPMCAS-M and HPMC, but not PVP-VA, markedly promoted etravirine supersaturation and inhibited drug precipitation. The supersaturation index EGF showed that each 0.1% HMCAS-M and 0.1% HPMC outperformed PVP-VA, by almost 2-fold, to maintain etravirine in solution (i.e., HPMCAS-M EGF = 5.2, HPMC EGF = 5.0, while PVP-VA EGF = 3.1). HPMCAS-M delayed T –10% by almost twice the time compared to HPMC, which in turn delayed T –10% by over 5-fold when compared to PVP-VA, at both concentrations of predissolved polymers. The addition of more PVP-VA (e.g., 0.05% vs 0.1%) did not improve the performance of this polymer, unlike HPMC and HPMCAS-M, where additional polymer further reduced the T –10% time. The hypothesized mechanism for the performance of HPMCAS-M and HPMC in promoting drug supersaturation and preventing drug crystallization is decreased etravirine motility and suppression of etravirine nucleation and precipitation. Previous studies have shown agreement between strong intermolecular interactions observed through NMR and the inhibition of drug precipitation. For example, HPMCAS-H suppressed carbamazepine molecular motility and suppressed precipitation, via strong drug–polymer interactions. In addition, molecular interactions between poly(acrylic acid) and ketoconazole reduced molecular mobility and prevented crystallization in liquid state NMR and dissolution experiments. In contrast, other studies involving a weakly basic and an anionic polymer showed strong interactions to be a relative detriment. For example, interactions between HPMCAS-H grade and itraconazole not only promoted retardation of drug precipitation but also notably promoted higher stabilization of itraconazole that limited drug dissolution/permeation. In addition, ionic interactions, such as between loratadine and HPMCAS-M, can result in poor drug release. The NMR experiments here did not aim to mimic gastrointestinal physiology; instead, the NMR experimental approaches described here are a screening tool and are used to streamline polymer selection to sustain drug supersaturation for further in vitro studies. Etravirine is formulated with HPMC in tablet product Intelence. The results here show that this polymer has strong molecular interactions in HNMR experiments and successfully maintained etravirine in solution in supersaturation studies. HPMCAS-M outperformed HPMC here and, although more recently introduced as a commercial excipient, appears here as an alternative, viable polymer to HPMC to fabricate an etravirine ASD.   Conclusions The objective of this study was to devise a 1 HNMR approach that identifies polymers that promote supersaturation and prevent crystallization of etravirine. 1 HNMR techniques STD-NMR and T 1 relaxation predicted HPMC and HPMCAS-M as viable polymers for etravirine via high drug–polymer binding, while PVP-VA was predicted to be nonviable. These predictions were challenged in supersaturation studies using the solvent-shift methodology. Supersaturation studies agreed with STD-NMR and T 1 relaxation time predictions, as HPMC and HPMCAS-M maintain etravirine in solution for longer time than PVP-VA. The results show promise of 1 HNMR to streamline polymer selection in a nondestructive and resource sparing fashion for subsequent ASD development.   