Pharmacokinetics of nevirapine and lamivudine in patients with HIV-1 infection.

The purpose of this parallel treatment group, double-blind, multicenter study was to characterize the pharmacokinetics of nevirapine and lamivudine when coadministered to patients with the HIV-1 infection. This pharmacokinetic interaction study was nested within a larger Phase III clinical trial conducted to characterize the safety and efficacy of coadministered nevirapine and lamivudine. One hundred HIV-1 infected patients with CD4+ lymphocyte counts < 200 cells/mm3and who were on a background of nucleoside (zidovudine [ZDV], didanosine [ddI], zalcitabine [ddC], stavudine [d4T]) therapy were randomly assigned to be treated with either nucleoside + lamivudine + nevirapine or nucleoside + lamivudine + placebo. Each patient underwent blood sampling at defined times for the purpose of determining the concentration of nevirapine in plasma and lamivudine in serum under steady-state conditions. Each patient was also monitored closely for concomitant administration of other drugs, including ZDV, ddI, ddC, d4T and cotrimoxazole. The pharmacokinetics of nevirapine and lamivudine were characterized using nonlinear mixed-effects modeling. There were no reported serious adverse events during the 40-day pharmacokinetic study. The results of the modeling analysis revealed that nevirapine had no effect on the pharmacokinetics of lamivudine. Estimates of the apparent clearance for nevirapine (CL/F = 3.3 L/hour; 95% confidence interval [CI] 2.9 to 3.7 L/hour) and lamivudine (CL/F 27.6 L/hour; 95% CI 22 to 33.2 L/hour) were consistent with the values reported in earlier trials. However, the results also showed that concomitant administration of lamivudine with cotrimoxazole resulted in a 31% reduction in the apparent clearance of lamivudine, resulting in a 43% increase in the average steady-state lamivudine serum concentrations. These results indicate that chronic concurrent administration of cotrimoxazole with lamivudine may significantly affect the steady-state pharmacokinetics of lamivudine.

Single dose pharmacokinetics and bioavailability of nevirapine in healthy volunteers.

The results of two randomized, single-dose, crossover bioavailability studies are presented which describe the pharmacokinetics and oral bioavailability of nevirapine, a novel nonnucleoside antiretroviral drug. In the first study 12 healthy male volunteers received nevirapine 15 mg via short-term i.v. infusion or orally as a 50 mg tablet or reference solution (50 mg/200 mL). Following the i.v. dose, nevirapine had a low systemic clearance (Mean +/- S.D., Cl = 1.4 +/- 0.3 L/h) and a prolonged elimination phase (t(1/2beta) = 52.8 +/- 14.8 h; MRT = 81.4 +/- 22.4 h). Nevirapine absolute bioavailability was 93 +/- 9% and 91 +/- 8% for the tablet and oral solution, respectively. In the second study, 24 healthy male volunteers were administered nevirapine as a 200 mg production-line tablet or oral reference solution (200 mg/200 mL). There was no significant difference in bioavailability between the tablet and reference solution. Overall, comparison of the pharmacokinetic parameters between the 50 and 200 mg doses indicates that nevirapine is well absorbed at clinically relevant doses. The absorption profiles using deconvolution revealed no evidence of differential enzyme induction between the two doses or routes of administration following a single dose.

Prediction of acetaminophen level from clinical history of overdose using a pharmacokinetic model.

A retrospective study was undertaken to determine the accuracy of predicting acetaminophen levels using the pharmacokinetic equation for first-order absorption and elimination of a single oral ingestion, (Formula: see text) Forty-four acute adult acetaminophen overdoses were studied during a 22-month period. Eighty levels drawn from 0 to 16 hours after ingestion were evaluated. To standardize the data, only first levels drawn in patients without prior spontaneous or ipecac-induced vomiting were analyzed (n = 26). Of these 26 levels, eight (31%) were drawn from 0 to two hours after ingestion, eight (31%) from two to four hours, and ten (38%) from four to 16 hours, with correlations of 0.59, 0.85, and 0.98, respectively. To determine the accuracy of predicting four-hour levels, five patients with first levels drawn at four hours, prior to vomiting, were evaluated. Substituting appropriate constants, the condensed equation, Cp4h = (0.59) (mg/kg dose), was used to predict the four-hour level (r = 0.99). Preliminary data suggest the ability to accurately predict four-hour acetaminophen levels from ingestion history alone using pharmacokinetic equations.