A non‐human 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: I. Dose‐finding study

Summary Two combined injections of levonorgestrel butanoate (4 mg/kg) and testosterone buciclate (8 mg/kg) at 3-month intervals to adult male baboons initiated a decrease in sperm concentration from baseline values of 490times106/ml to minimum values of 17times106/ml. This suppression was sustained until week 32, during which time between one and three azoospermic samples were collected from each of four out of five treated baboons in the period 10–24 weeks. Circulating plasma levels of LH and testosterone decreased to approximately 20–75% of baseline values. Plasma levels of cortisol declined to significantly reduced levels at weeks 22 and 36–44. All values returned to the baseline range by week 48. The combined administration of progestogen and androgen induced a more marked and sustained suppression to severe oligozoospermia or azoospermia than did the equivalent dose of progestogen alone (Goncharov et al., 1995). Although the dose of testosterone buciclate used did not maintain peripheral levels of testosterone in the normal range, it did not restimulate spermatogenesis. It was concluded that a combination drug regimen based on the novel long-acting levonorgestrel and testosterone esters could provide a contraceptive option for men.