Intramuscular testosterone undecanoate and norethisterone enanthate in a clinical trial for male contraception

Recent trials for hormonal male contraception are based on gestagens or GnRH antagonists combined with oral or injectable testosterone substitution. However, the efficacy of most trials remained disappointing. Norethisterone enanthate (NETE) has been used as a long-acting injectable female contraceptive and has shown sustained suppression of spermatogenesis in male monkeys and prolonged suppression of gonadotropins in men. This study was designed to prove the efficacy of the long-acting testosterone undecanoate ester (TU) alone or in combination with NETE in a phase II clinical trial. Fourteen healthy men received injections of 1000 mg TU in combination with injections of 200 mg NETE every 6 weeks over a period of 24 weeks, followed by a control period of 28 weeks. Another 14 volunteers received TU alone. During the study semen variables, reproductive hormones, clinical chemistry and lipid parameters, well-being, and sexual function were monitored. Scrotal content and prostates were checked sonographically. During the entire treatment period mean testosterone serum concentrations remained within the normal limits. Marked suppression of gonadotropins in both treatment groups resulted in azoospermia in 7 of 14 and 13 of 14 volunteers and in oligozoospermia in 7 of 14 and 1 of 14 in the groups given TU only or TU/NETE, respectively. However, the highest azoospermia rate in the TU/NETE group was achieved 8 weeks after the end of the treatment period, and 1 volunteer with very high initial sperm counts (mean, 190 million/mL at baseline) remained oligozoospermic (10.2 million/mL). From week 20 to week 24 there was a significant, fully reversible maximum weight gain of 3.7 kg, on the average, in the NETE group. In the NETE and TU alone groups there were significant 26.6% and 11.5% maximum decreases in high density lipoprotein cholesterol compared with baseline values during the treatment period. A significant elevation of low density lipoprotein and a decrease in lipoprotein(a) were detected in the TU/NETE group. In conclusion, combination treatment with NETE showed suppression of spermatogenesis comparable with results using testosterone esters in combination with GnRH antagonists or cyproterone acetate, but had more favorable injection intervals and better efficacy. Because of its long-lasting, profound suppression of spermatogenesis and the absence of serious side-effects, the combination of TU and NETE can be considered a first choice for further studies of hormonal male contraception.