Eligible subjects were healthy males aged 21 to 55 years (study 1) or healthy male or female subjects aged 18 to 55 years (study 2), who had a body mass index (BMI) of 18 to 30 kg/m2 (study 1) or 17.5 to 30.5 kg/m2 (study 2) and a total body weight of >45 kg (study 1) or >50 kg (study 2). Subjects with a history of significant disease, HIV infection, or hepatitis B or C were excluded. Prescription and nonprescription drugs, vitamins, and dietary supplement medications were not permitted during the study and had to be discontinued within 7 days or 5 half-lives (whichever was longer) prior to the first dose of study medication.
These were phase I, open, randomized, two-way crossover (study 1; study A5271008) or three-way crossover (study 2; study A5271043) studies conducted at the Pfizer Singapore Clinical Research Unit to investigate the effect of oral doses of rifampin (study 1) and rifabutin (study 2) on the steady-state PKs of lersivirine and the effect of lersivirine on the PKs of rifabutin and 25-O-desacetyl-rifabutin (the active metabolite of rifabutin) (study 2). The studies consisted of a screening visit up to 28 days before the start of dosing, two 14-day treatment periods (study 1; ), or three 10-day treatment periods (study 2; ) with a minimum washout period of 14 days between each.
In study 1, subjects received lersivirine at 1,000 mg q.d. on days 1 to 10 and 1,000 mg twice a day (BID) on days 11 to 13, with a single dose given on the morning of day 14 during both treatment periods in the fasted state. On days 1 to 14, subjects received rifampin at 600 mg q.d. in one period and placebo q.d. in the other period, according to randomization, with the morning dose of lersivirine. Only the PK and adverse event (AE) data relating to lersivirine administered q.d. are presented in this report. In study 2, subjects were randomized to receive lersivirine at 1,000 mg q.d. alone, rifabutin at 300 mg q.d. alone, and lersivirine at 1,000 mg q.d. and rifabutin 300 mg q.d. combined, in a random order across the three treatment periods. In study 2, lersivirine and rifabutin were administered with a meal, as it has been shown that food may help increase rifabutin tolerability. Administration with food does not significantly affect the exposures of lersivirine or rifabutin (8
Investigator site personnel administered the study treatment during each period with water at ambient temperature to a total volume of 240 ml. Subjects were asked to swallow the whole tablet or capsule and not chew it prior to swallowing. In order to standardize the conditions on PK sampling days, all subjects were required to refrain from lying down (except when required for blood pressure, pulse rate, and electrocardiographic measurements), eating, and drinking beverages other than water during the first 4 h after dosing. The mouth of each subject was examined following dosing to ensure that the study medication was taken.
Sampling and analytical methods.
In study 1, blood samples were collected on days 1, 9, 11, and 13 at 0 h (predose), on day 10 at 0 h (predose) and at 0.5, 1, 2, 3, 4, 6, 8, 10, 12, 18, and 24 h postdose, and on day 14 at 0 h (predose) and at 0.5, 1, 2, 3, 4, 6, 8, 10, and 12 h postdose. In study 2, blood samples were collected on day 10 at 0 h (postdose) and 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 h postdose.
In studies 1 and 2, blood samples of 5 ml and 4 ml, respectively, were taken to provide a minimum of 2 ml plasma for lersivirine PK analysis and transferred into appropriately labeled tubes containing lithium heparin. In addition, for study 2, blood samples of 6 ml were taken to provide a minimum of 2.5 ml plasma for rifabutin and 25-O-desacetyl-rifabutin PK analysis and were transferred into appropriately labeled tubes containing sodium heparin. All samples were centrifuged at approximately 1,700 × g for 10 min at 4°C. Plasma was stored in appropriately labeled screw-cap polypropylene tubes at approximately −20°C within 1 h of collection. Samples were analyzed using solid-phase extraction and a validated high-performance liquid chromatography/dual mass spectrometry (HPLC/MS/MS) assay.
The assay precision was 5.5% (coefficient of variance [CV]; study 1) and ≤8.5% (study 2) for lersivirine, ±69.9% (±10.3% without one potential outlier) for rifabutin (study 2), and ±9.3% for 25-O-desacetyl-rifabutin (study 2). The between-day assay accuracy (percent relative error [RE]) of the estimated quality control samples ranged from −5.6% to 2.4% (study 1) and −3.3% to 6.3% (study 2) for lersivirine, −6.5% to 21.7% (1.1% without one potential outlier) for rifabutin (study 2), and −4.8% to 5.7% for 25-O-desacetyl-rifabutin (study 2). Calibration ranges were 1.0 to 2,000 ng/ml for lersivirine (studies 1 and 2), 2.5 to 1,000 ng/ml for rifabutin (study 2), and 1.0 to 1,000 ng/ml for 25-O-desacetyl-rifabutin (study 2).
Safety evaluations included AE monitoring, laboratory safety tests, liver function tests (study 1), and single 12-lead electrocardiogram, supine blood pressure, and pulse rate recording.
In study 1, a minimum sample size of 12 was required to provide 90% confidence intervals (CIs) for the difference between treatments of ±0.0539 and ±0.1525 on the natural log scale for area under the plasma concentration-time profile from time zero to infinity postdose (AUCτ) and maximum plasma concentration (Cmax), respectively, with 80% coverage probability. The above-described calculations assumed the estimated intrasubject standard deviations of the natural log of the area under the plasma concentration-time profile from time zero to 24 h postdose (AUC24) and Cmax to be 0.089 and 0.252, respectively, for lersivirine.
To estimate the effect of rifabutin on the PKs of lersivirine (study 2), the effect of lersivirine on the PKs of rifabutin, and the effect of lersivirine on the PKs of 25-O-desacetyl-rifabutin in study 2, 18 subjects were required to provide 90% CIs for the difference between treatments of ±0.101 and ±0.140, ±0.098 and ±0.159, and ±0.105 and ±0.152, respectively, on the natural log scale for AUC24 and Cmax, respectively, with 90% coverage probability. The calculations described above assumed the estimated intrasubject standard deviations of natural log AUC24 and Cmax to be 0.155 and 0.215, respectively, for lersivirine, 0.150 and 0.244, respectively, for rifabutin, and 0.161 and 0.234, respectively, for 25-O-desacetyl-rifabutin.
The PK parameters AUC24, plasma concentration observed at 24 h postdose (C24), Cmax, and time to Cmax (Tmax) were summarized by treatment. An ad hoc analysis was performed to assess the elimination half-life (t1/2) for lersivirine in the presence of rifampin and rifabutin. AUC parameters were determined using the linear/log trapezoidal method, and Cmax, C24, and Tmax were determined by observation. Natural log-transformed data were analyzed using a mixed-effect model with sequence, period, and treatment as fixed effects and subject within sequence as a random effect. The adjusted geometric mean for each treatment was obtained by exponentiation of the mean estimate on the natural log scale obtained from the model. Estimates of the adjusted mean differences (test/reference) and the corresponding 90% CIs were obtained from the model. The adjusted mean differences and 90% CIs for the differences were exponentiated to provide estimates of the ratio of adjusted geometric means (test/reference), where the test was lersivirine plus rifampin (study 1) or lersivirine plus rifabutin (study 2) and the reference was lersivirine plus placebo (study 1), lersivirine alone (study 2), or rifabutin alone (study 2).