New injectable testosterone ester maintains serum testosterone of castrated monkeys in the normal range for four months

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Abstract
Two groups of four long-term orchidectomized cynomolgus monkeys, Macaca fascicularis, weighing 2.8-4.6 kg received either a single intramuscular injection of 40 mg of a new testosterone ester, testosterone-trans-4-n-butylcyclohexyl-carboxylase (20 Aet-1) in an aqueous suspension or 32.8 mg testosterone oenanthate dissolved in sesame oil. Both preparations contained equal amounts of testosterone, namely 23.6 mg. Testosterone oenenthate injections resulted in supraphysiological serum testosterone levels for eight days followed by a rapid decline so that the lower physiological limit was reached after three weeks. In contrast, 20 Aet-1 produced a moderate increase of serum testosterone levels into the physiological range. Serum testosterone remained in this range for a period of 18 weeks. Thus, it appears that the 20 Aet-1 may provide a long desired, new modality of testosterone substitution for hypogonadal men as well as for methods of male fertility control.