Comparison of a gonadotropin releasing-hormone antagonist plus testosterone (T) versus T alone as potential male contraceptive regimens.

Efforts to develop a hormonal contraceptive regimen for men have focused on administration of testosterone (T), alone or together with other agents. Previous regimens have successfully induced azoospermia in only 50-70% of subjects, however. GnRH antagonists, alone or in combination with T, have been shown to induce azoospermia in a very high percentage of nonhuman primates. We tested the hypothesis that the addition of a GnRH antagonist to a high-dose T regimen would lead to a higher percentage of men developing azoospermia than would T alone. We administered the GnRH antagonist, Nal-Glu (100 micrograms/kg.day sc), plus T enanthate, 200 mg im weekly or placebo sc injections daily plus T enanthate, 200 mg im weekly, to separate groups of healthy men for 16-20 weeks. Seven of 10 men who received Nal-Glu plus T and 6 of 9 men who received T alone became azoospermic; gonadotropin levels were suppressed and T levels were increased similarly in both groups. There was a trend toward higher pretreatment gonadotropin levels and lower sperm counts in men who became azoospermic. Weight gain, development of acne, and increases in hematocrit and hemoglobin were similar in the two groups. In the majority of the men, sperm counts returned to the baseline levels within 4-5 months after treatment ended. We conclude that with the dosages of Nal-Glu and T we used in this study, the addition of GnRH antagonist to a high-dose T regimen does not increase the ability of T to suppress spermatogenesis in healthy men. Use of a higher dose of Nal-Glu, a lower dose of T, delaying the start of T replacement until several weeks after Nal-Glu injections are initiated, or prolonged hormonal administration might lead to a combination regimen that will suppress spermatogenesis more fully than does T alone.