Relative Bioavailability and Pharmacokinetics: A Combination of Pentazocine and Acetaminophen

Abstract

The relative bioavailability and pharmacokinetics of a combination product containing pentazocine and acetaminophen were studied in 20 healthy human males. Each subject, in a single-dose three-way crossover design, received two different preparations containing 50mg of pentazocine (as base) and 1300mg of acetaminophen either as capsule-shaped tablets or as a solution. Plasma concentrations of pentazocine and acetaminophen were determined from 0.25 to 12h following oral administration. The plasma data for both compounds in the tablet formulation were described by an open one-compartment body model with first-order absorption. The average (±SD) bioavailability of the tablet relative to that of the solution was 85.0 ± 31.1 and 88.6 ± 13.1% for pentazocine and acetaminophen, respectively. The apparent first-order regression-dependent elimination rate constants for pentazocine from the tablet and solution preparations were 0.19 ± 0.08 and 0.20 ± 0.06h−1, respectively, while the rate constants for acetaminophen were 0.26 ± 0.03 and 0.25 ± 0.03h−1 for the tablet and solution preparations, respectively. These rate constants correspond to terminal elimination half-lives of ~3.6h for pentazocine and ~2.7h for acetaminophen.