Finasteride, A Steroid 5α‐Reductase Inhibitor, Does Not Affect the Oxidative Metabolism of Antipyrine

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Abstract
A single‐blind study was conducted to investigate the effect of multiple doses of finasteride, a 5α‐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.