Two whole blood samples (0.5 mL) were obtained at steady state (day 3 of therapy or later), collected in K3EDTA mini-collection tubes labeled with a sample identification number. Plasma specimens were separated by centrifugation of 1500 g for 10 minutes at 4 degrees Celsius within 60 minutes of sample collection. Plasma supernatant was transferred into a cryovial labeled with the same sample identification number. Cryovials were immediately stored at -70 degrees Celsius. Sample obtainment and processing was directly supervised by the principle investigator.