Pharmacokinetics of sulphinpyrazone and its major metabolites after a single dose and during chronic treatment

Summary The pharmacokinetics of bupropion and 3 of its basic metabolites were determined in 8 young, healthy, male volunteers after single and multiple oral doses of bupropion. Plasma profiles were obtained: 1) after a single 100 mg oral dose of bupropion hydrochloride, 2) following administration of 100 mg 8-hourly for 14 days and 3) again after a single 100 mg dose 14 days later. Plasma concentrations of the parent drug and metabolites were determined by high-performance liquid chromatography. Saliva secretion and pupil diameters were measured, subjective assessments of sleep made using visual analogue scales and side effects, blood counts and biochemistry were monitored. After the first dose mean elimination half lives (t_1/2) of bupropion, and metabolites I and II were 8, 19 and 19 h respectively. On repeated administration there was little accumulation of the parent drug and no evidence for induction of its own metabolism. Accumulation of I was consistent with its rate of elimination after single doses while that of II was greater than predicted with prolongation of t_1/2 to 35 h. Metabolite III was barely detectable after single doses but its accumulation on multiple dosing was consistent with its long half life (35 h) determined on occasion 2. Saliva secretion was significantly reduced during the multiple dosing period but there were no complaints of dry mouth. Subjective assessments of sleep were not significantly altered though one subject reported vivid dreams. There were no other adverse reactions.Abbreviations k_a first order rate constant for absorption or appearance - k_el first order rate constant for elimination - F extent of bioavailability - D administered dose (as free base) - k₁₂ first order distribution rate constant into peripheral compartment - k₂₁ first order distribution rate constant from peripheral compartment - k₁₀ first order elimination rate constant from central compartment - first order elimination rate constant of rapid disposition phase - first order elimination rate constant of slow disposition phase - V_z apparent volume of distribution - V_c apparent volume of distribution of central compartment - t time after drug administration - t_o lag time for absorption - Cp_(t) concentration in plasma at time t - n number of doses - Cp_(tn) concentration in plasma at time t after n^th dose - dose interval - CL clearance uncorrected for bioavailability F