A Nonhuman Primate Study (Baboon, Papio-Hamadryas) To Determine If A Long-Acting Progestogen, Levonorgestrel Butanoate, Combined With A Long-Acting Androgen, Testosterone Buciclate, Can Suppress Spermatogenesis .1. Dose-Finding Study

This study in adult male baboons was conducted to establish the dose of a long-acting progestogen, levonorgestrel butanoate, and that of a long-acting androgen, testosterone buciclate, which, when combined, would achieve optimal and prolonged suppression of spermatogenesis. Two intramuscular injections of levonorgestrel butanoate at 3-month intervals and in the dose range 1-8 mg/kg reduced sperm production and plasma concentrations of testosterone, LH and FSH for periods of up to 6 months. The suppression of sperm production was greatest and most prolonged in the 4 mg/kg group. Two intramuscular injections of testosterone buciclate at 3-month intervals, and at doses of 4 and 8 mg/kg, induced variable changes in circulating levels of testosterone, elevated by the higher dose, and caused sperm suppression, in some animals to azoospermia. It was concluded that 8 mg/kg testosterone buciclate would provide adequate androgen replacement when combined with 4 mg/kg levonorgestrel butanoate as a putative male contraceptive regimen.