Pharmacokinetic evaluation of drug interactions with zidovudine. I: Probenecid and zidovudine in monkeys

Pharmacokinetic evaluation of a drug interaction between zidovudine (AZT) and probenecid was conducted in monkeys. Six animals received 20 mg/kg of AZT as single intragastric (ig) and iv doses in the absence and presence of 50 mg/kg of probenecid administered ig. Plasma concentrations of AZT and its 5′‐glucuronide metabolite (AZTG) were quantitated for 12 h by HPLC. Amounts of AZT and AZTG in urine were also measured, as were probenecid plasma concentrations. Non‐compartmental methods were used to obtain pharmacokinetic parameters for AZT and AZTG. In the presence of probenecid, the total clearance of AZT decreased by 50%, renal clearance decreased, and elimination half‐life increased. The volume of distribution at steady‐state and systemic bioavailability of AZT were not significantly altered by probenecid. The areas under the plasma concentration‐time curves and terminal half‐lives of AZTG were increased, and renal clearances of AZTG were decreased. The alterations in AZT and AZTG pharmacokinetic parameters are consistent with inhibition of metabolism and renal tubular secretion by probenecid. Since AZT was administered by both oral and iv routes, clearance, volume of distribution, and bioavailability parameters were independently determined. Based on data reported for humans on the zidovudine‐probenecid interaction, monkeys appear to be appropriate animal models for the evaluation of zidovudine drug interactions.