Enclomiphene, an estrogen receptor antagonist for the treatment of testosterone deficiency in men.

Enclomiphene (Androxal), in development by Repros Therapeutics Inc, is a non-steroidal estrogen receptor antagonist that promotes gonadotropin-dependent testosterone secretion by the testes. Enclomiphene constitutes the trans-stereoisomer of clomiphene citrate, a drug that has been widely prescribed for several decades for the treatment of female ovulatory dysfunction. Because of the antagonistic effects of enclomiphene, the drug has the potential to increase serum testosterone levels in men with secondary hypogonadism by restoring physiological endogenous testosterone secretion while maintaining testicular volume and, potentially, spermatogenesis. In clinical trials conducted to date, enclomiphene demonstrated significant efficacy in the physiological restoration of testosterone levels in males with secondary hypogonadism. The compound also exhibited an unanticipated favorable effect on fasting plasma glucose; this result has been accompanied by rapidly accumulating evidence from other researchers for a bidirectional relationship between low serum testosterone and obesity/metabolic syndrome (syndrome X) in men. Short-term clinical safety data for enclomiphene have been satisfactory and equivalent to safety data for testosterone gels and placebo. Enclomiphene demonstrates promise in the management of secondary hypogonadism associated with obesity, metabolic syndrome and, possibly, infertility, and should undergo placebo-controlled, randomized clinical trials for these indications.