Pharmacokinetics of pentazocine in the rhesus monkey

The time course of pentazocine concentration was followed in the plasma and cerebrums of individual monkeys by obtaining serial samples of both tissues after intravenous administration of tritiated drug. Plasma concentrations of pentazocine were also followed in a monkey after portal vein infusion. A three-compartment open-system model adequately fits the observed plasma data. The use of the constants derived from that model to predict the time course of pentazocine concentration in the brain results in a good fit with the observed cerebral concentrations. As expected, portal vein infusion caused a reduction in the area below the plasma concentration-time curves and in the percentage of pentazocine excreted in the urine. The relative proportions of known metabolites and their conjugates in urine were determined.