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The Effect of 5-Reductase Inhibition with Dutasteride and Finasteride on Semen Parameters and Serum Hormones in Healthy Men

Department of Medicine (J.K.A., B.D.A., A.M.M., W.J.B.), Veterans Affairs-Puget Sound Health Care System (B.D.A., A.M.M.), and Geriatric Research, Education, and Clinical Center (A.M.M.), University of Washington, Seattle, Washington 98195; Department of Clinical Pharmacology (S.E.W., L.J.H., R.V.C.), GlaxoSmithKline Research and Development, Research Triangle Park, North Carolina 27709; and Department of Medicine (R.S.S., C.W.) and General Clinical Research Center (C.W.), Harbor-University of California, Los Angeles Medical Center, Torrance, California 90509

Address all correspondence and requests for reprints to: Dr. Richard V. Clark, Clinical Pharmacology-Metabolic Discovery Medicine, GlaxoSmithKline Research and Development, Five Moore Drive, 17.1356H, P.O. Box 13398, Research Triangle Park, North Carolina 27709-3398.

Context: Dutasteride and finasteride are 5-reductase inhibitors (5ARIs) that dramatically reduce serum levels of dihydrotestosterone (DHT).

Objective: Because androgens are essential for fertility, we sought to determine the impact of 5ARI administration on serum testosterone (T), DHT, and spermatogenesis.

Design, Setting, Subjects, and Intervention: We conducted a randomized, double-blinded, placebo-controlled trial in 99 healthy men randomly assigned to receive dutasteride (D; 0.5 mg) (n = 33), finasteride (F; 5 mg) (n = 34), or placebo (n = 32) once daily for 1 yr.

Main Outcome Measures: Blood and semen samples were collected at baseline and 26 and 52 wk of treatment and 24 wk after treatment and were assessed for T, DHT, and semen parameters.

Results: D and F significantly (P < 0.001) suppressed serum DHT, compared with placebo (D, 94%; F, 73%) and transiently increased serum T. In both treatment groups, total sperm count, compared with baseline, was significantly decreased at 26 wk (D, –28.6%; F, –34.3%) but not at 52 wk (D, –24.9%; F, –16.2%) or the 24-wk follow-up (D, –23.3%; F, –6.2%). At 52 wk, semen volume was decreased (D, –29.7%; F, –14.5%, significantly for D) as was sperm concentration (D, –13.2%; F, –7.4%, neither significant). There was a significant reduction of –6 to 12% in sperm motility during treatment with both D and F and at follow-up. Neither treatment had any effect on sperm morphology.

Conclusions: This study demonstrates that the decrease in DHT induced by 5ARIs is associated with mild decreases in semen parameters that appear reversible after discontinuation.

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