Pharmacodynamic Modeling of Finasteride, a 5α‐Reductase Inhibitor

Abstract

Finasteride is a 4‐azasteroid inhibitor of one isoenzyme of 5α‐reductases that converts testosterone to dihydrotestosterone (DHT). We characterized the time course of DHT concentrations. The following model was used to assess DHT pharmacodynamics: where joint fitting of three dose levels yielded k o in = 28% change/hour, k out = 0.28 hour 1 , IC 50 = 0.012 ng/ml, and E max = 0.7. The modification of a previous model with the maximum partial effect factor, E max , may be useful in characterizing the pharmacodynamics of drugs with similar indirect mechanisms.