title: Bioavailability and first-pass metabolism of oral pentazocine in man.
abstract: The bioavailability of oral pentazocine was studied in 5 healthy volunteers. Plasma concentrations were determined from 30 min up to 6 hr following oral administration (two 50-mg tablets) and, at other occasions, after intravenous injection of 30 mg pentazocine. The average bioavailability was found to be 18.4 +/- 7.8% (SD, n = 5). It is shown that this low bioavailability depend almost entirely on the first-pass metabolism of pentazocine following oral administration by application of intravenous clearance concepts. The average beta-phase half-life was about the same following intravenous administration, 203 +/- 71 (SD, n = 5) min as following oral administration, 177 +/- 34 (SD, n = 5) min, with a total volume of distribution of 5.56 +/- 1.63 (SD, n = 5) L/kg. It is suggested that the variations in bioavailability of orally administered pentazocine have the potential to contribute to variations in pharmacologic effects in patients.
mesh_terms: D000284:Administration, Oral; D001682:Biological Availability; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D008954:Models, Biological; D010423:Pentazocine / Q000008:administration & dosage / Q000378:metabolism*; D013997:Time Factors
chemical_list: D010423:Pentazocine