ASSESSMENT OF THE PHARMACOKINETIC-PHARMACODYNAMIC INTERACTION BETWEENTERAZOSIN AND FINASTERIDE

The pharmacokinetic-pharmacodynamic interaction between terazosin and finasteride was evaluated in an 18-day, parallel, open-label, randomiz ed study. Forty-eight nonsmoking, healthy, adult male volunteers enter ed the study. One third of the participants received terazosin alone, one third received terazosin and finasteride, and one third received f inasteride alone. Multiple-dose coadministration of terazosin and fina steride did not alter the central values of steady-state pharmacokinet ic parameters of either drug in a statistically significant manner. Co mpared with the single-agent groups, however, the group taking finaste ride and terazosin had higher variability in the pharmacokinetic param eters of both drugs. Testosterone concentrations were not altered afte r administration of finasteride and terazosin alone or in combination. Terazosin administered alone did not affect the dihydrotestosterone c oncentrations. The significant reduction in dihydrotestosterone concen trations induced by administration of finasteride was not affected by coadministration of terazosin. Mean changes in blood pressure and puls e rate in these normotensive volunteers were generally slight; therefo re, concurrent administration of multiple doses of terazosin and finas teride did not produce significant clinical concern.