Investigation of a novel preparation of testosterone decanoate in men: pharmacokinetics and spermatogenic suppression with etonogestrel implants.

We have investigated the pharmacokinetics and effects on the male reproductive axis of a novel preparation of testosterone decanoate (TD) with a progestogen implant. Twenty healthy Chinese men were administered TD (400 mg intramuscular 4 weekly) with two subcutaneous (SC) etonogestrel implants. Trough testosterone concentrations rose with repeated administration. Peak concentrations 1 week after the fourth injection were 31 +/- 2 nmol/liter. Both LH and FSH were rapidly suppressed and continued to fall during treatment. Spermatogenesis was also suppressed, to <or=1 x 10(6)/mL in all men with 16 (80%) azoospermic at 12 weeks. Treatment was associated with an increase in weight, and also increases in hemoglobin concentration (9%) and hematocrit (15%). No subjects withdrew from the study, although the study was terminated after subjects had completed 12 to 18 weeks as some men were found to have elevated liver enzyme tests. These data demonstrate that the pharmacokinetics of TD are improved compared to previous injectable testosterone preparations, although peak testosterone concentrations rise briefly into the supraphysiological range. The speed and degree of spermatogenic suppression suggest that this combination has promise as an effective male contraceptive.