Quinidine does not alter antipyrine metabolism

Effects of atorvastatin, an HMG-CoA reductase inhibitor, on hepatic oxidative metabolism of antipyrine

Possible effects of multiple-dose administration of atorvastatin on the pharmacokinetics of single-dose antipyrine were evaluated in this drug-drug interaction study. Twelve healthy male volunteers received three 200-mg capsules of antipyrine on days 1 and 22, and two 40-mg atorvastatin tablets in the morning on days 8 through 23. Serial blood and urine samples were collected after administration of each antipyrine dose. Plasma was analyzed for antipyrine, and urine samples were analyzed for antipyrine, 4-hydroxyantipyrine, and norantipyrine by validated high-performance liquid chromatography with ultraviolet detection. Overall, antipyrine and atorvastatin doses were well tolerated in healthy volunteers. Mean antipyrine concentrations in plasma after administration of a single, oral dose of antipyrine during coadministration of multiple doses of atorvastatin were nearly superimposible on concentrations after administration of antipyrine alone. Individual and mean parameter values for plasma pharmacokinetics of antipyrine were similar in both treatment periods. Atorvastatin did not significantly alter the fraction of clearance of antipyrine in plasma that occurred by urinary excretion of 4-hydroxyantipyrine and norantipyrine. These results indicate that the recommended highest daily dose of atorvastatin has negligible effects on antipyrine pharmacokinetics and on oxidative pathways responsible for the metabolism of antipyrine.

Finasteride, a steroid 5 alpha-reductase inhibitor, does not affect the oxidative metabolism of antipyrine

A single-blind study was conducted to investigate the effect of multiple doses of finasteride, a 5 alpha-reductase inhibitor for the treatment of benign prostatic hyperplasia, on the single-dose pharmacokinetics of antipyrine. Twelve patients with benign prostatic hyperplasia received a total of four single oral doses of 18 mg/kg antipyrine before, during, and after treatment with 10 mg/day of finasteride for 28 days. Finasteride had no effect on antipyrine concentration profiles. There were also no changes in urinary excretion of three principal antipyrine metabolites. A slight increase in renal clearance of antipyrine was observed; however, this is not considered relevant because excretion of unchanged antipyrine represents a minor fraction of total elimination and is not directly related to oxidative metabolism. These results imply that significant interactions between finasteride and drugs metabolized by these cytochrome P-450 enzymes are unlikely.

The pharmacokinetics of antipyrine and three of its metabolites in the rabbit: intravenous administration of pure metabolites

Antipyrine (AP) is a commonly used probe of oxidative metabolism. Indirect evidence demonstrates formation rate limited disposition of its metabolites. Kinetic studies using antipyrine and its major metabolites 3-hydroxymethylantipyrine (HMA), norantipyrine (NORA), and 4-hydroxyantipyrine (OHA) were completed to investigate the metabolic fate of preformed antipyrine metabolite and to demonstrate directly formation rate-limited metabolite disposition in vivo. Bolus injections of antipyrine and preformed metabolites (40-50 mg/kg) were administered to male, New Zealand white rabbits. Plasma and urine were analyzed using HPLC. These studies demonstrate that HMA, NORA, and OHA are formation rate limited in the rabbit. NORA appears to undergo further extensive oxidative and conjugative metabolism. Unknown additional peaks were detected in urine after NORA dosing but not after HMA or OHA administration. Mass spectroscopy of the unknown HPLC eluents identified potential structures of these NORA metabolites.