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## Drug Loading into Liposomes Containing 1.05 N Diethylammonium Sucrose Octasulfate 

Aqueous solution of 1.05 N diethylammonium sucrose octasulfate (DEA-SOS) pH 6.0, osmolarity 727 mmol/kg, was prepared using ion-exchange/titration method of Example 6 using neat diethylamine (99 .5% purity). The lipid matrix of3 molar parts DSPC, 2 molar parts Cholesterol, and 0.015 molar parts PEG2000-DSPE, was formulated into lipo› somes (volume-weighted average size 92.4 nm) in the pres› ence of DEA-SOS solution, and CPT-11 was loaded in the liposomes as various drug/lipid input ratios using the method of Example 11. Non-encapsulated drug was removed by gel› chromatography, and the amount of encapsulated drug per unit lipid ( drug/lipid output ratio) was determined. Encapsu› lation efficiency was calculated as% of drug/lipid output ratio relative to input ratio. The results are shown in Table 40. The loading achieved it’s maximum level of about 1.76 mo! drug per mo! phospholipid (1.67-1.70 mo! drug/g total lipid), which is in good agreement with the amount (1.78 mo! diethylammonium/mol phospholipid) based on the diethyammonium content of the liposomes, assuming stio› chiometric exchange of intraliposomal diethylammonium ions for the drug molecules and estimated intraliposomal entrapped volume of approximately 1.7 I/mo! phospholipid. 

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Unless indicated otherwise, the analytical data are pre› sented as the mean–standard error of triplicate runs. The rat plasma pharmacokinetic data are the mean–standard error of duplicate runs. 

Although the invention has been described with reference to the presently preferred embodiment, it should be under› stood that various modifications can be made without depart› ing from the spirit of the invention. Accordingly, the scope of $_{50 }$ the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all cited articles and references, including patent applications and publications, are incorporated herein by reference for all pur- 55 poses. 

What is claimed is: 

1. A liposomal composition comprising liposomes in an aqueous medium, the liposomes having an interior aqueous space separated from the aqueous medium by a membrane comprising 1,2-distearoyl-SN-phosphatidylcholine, choles› terol and N-(omega-methoxy-poly(ethylene glycol)-oxycar› bonyl)-1,2-distearoylphosphatidyl ethanolamine, and entrapped inside the liposomes are either: 1) irinotecan and sucrose octasulfate, or 2) irinotecan, sucrose octasulfate and a substituted anmionium compound; wherein, the irinotecan 

## Example 74 

entrapped inside the liposomes is at a concentration that exceeds the concentration of the irinotecan in the aqueous medium. 

2. The liposomal composition of claim 1, where irinotecan, sucrose octasulfate, and substituted anmionium compound are entrapped inside the liposomes and wherein the substi› tuted anmionium compound has a formula: R$_{1 }$-(R$_{2}$-)N+ (-R$_{3}$)-R$_{4}$ , wherein N is a an ammonium nitrogen atom, each ofRi, R$_{2}$ , R$_{3}$ , and R$_{4 }$ is independently a hydrogen atom or an organic group having each independently not more than 8 carbon atoms, and in totality not more than 18 carbon atoms inclusive, wherein at least one of Ri, R$_{2}$ , R$_{3}$ , and R$_{4 }$ is an organic group; wherein the organic group is independently alkyl, alkylidene, heterocyclic alkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl, or a hydroxy-substituted derivative thereof, optionally including S, 0, or N atoms forming an ether, ester, thioether, amine, or amide bond; and wherein at least three of Ri, R$_{2}$ , R$_{3}$ , andR$_{4 }$ are the organic groups; or at least one of the organic groups has a secondary or tertiary carbon atom directly linked to the anmionium nitrogen atom. 

3. The liposomal composition of claim 2, wherein the substituted ammonium compound is selected from the group consisting of isopropy lethylanmionium, isopropy lmethy !am› monium, diisopropylanmionium, tert-butylethylammonium, dicyclo-hexylanmionium, morpholinium, pyridinium, pip› eridinium, pyrrolidinium, piperazinium, tert-butylammo› nium, 2-ammonio-2-methyl-propanol-1,2-ammonio-2-me› thyl-propandiol-1,3, tris-(hydroxyethyl)-anmioniomethane, N,N’-diethyl-ethanolammonium, N,N’,N"-tris-(2-hydroxy- ethyl)ammonium, N,N’-bis-(2-hydroxyethyl)ethylammo- nium, trimethyl-ammonium, triethylanmionium, diethylm› ethyl-ammonium, diisopropylethylammonium, triisopropylammonium, N-methyl-morpholinium, 1-(2-hy› droxyethyl)piperidinium, 1-methylpyrrolidinium, l ,4-dim- ethyl-piperazinium, tetramethylammonium, tetraethyl-am› monium, and tetrabutylammonium. 

4. The liposomal composition of claim 2, wherein the substituted ammonium compound is triethylammonium. 

5. The liposomal composition of claim 2, wherein the substituted ammonium compound is diethylanmionium. 

6. The liposomal composition of claim 1, wherein the membrane comprises about 59 .8 mo!.% of the 1,2-distearoyl› SN-phosphatidylcholine; about 39.9 mo!. % of the choles› terol and about 0.3 mo!.% of the N-(omega-methoxy-poly ( ethylene glycol)-oxycarbonyl)-1,2-distearoylphosphatidyl ethanolamine. 

7. The liposomal composition of claim 6, wherein the poly(ethylene glycol) in the N-(omega-methoxy-poly(ethyl› ene glycol)-oxycarbonyl)-1,2-distearoylphosphatidyl etha› nolamine has a molecular weight of about 2,000. 

8. The liposomal composition of claim 1, wherein the composition is a fluid pharmaceutical formulation for parenteral administration. 

9. The liposomal composition of claim 1, wherein molar ratio of the irinotecan to the totality of the lipids is at least 1.0. 

10. The liposomal composition of claim 1, wherein the relative amounts of the irinotecan and the sucrose octasulfate are near the point of stoichiometric equivalency. 

11. The liposomal composition of claim 1, wherein the relative amounts of the irinotecan and the sucrose octasulfate are at the point of stoichiometric equivalency. 

12. The liposomal composition of claim 1, wherein the irinotecan and the sucrose octasulfate are comprised in the form of a salt. 

13. The liposomal composition of claim 1, wherein the aqueous medium comprises hydroxyethylpiperazine-ethyl› sulfonate (HEPES) and NaCl. 

