Subcutaneous Testosterone Anastrozole Therapy in Men: Rationale, Dosing, and Levels on Therapy

This analysis was designed to determine the efficacy of anastrozole, an aromatase inhibitor, combined with testosterone in a subcutaneous implant in preventing elevated estradiol levels and the subsequent side effects of excess estrogen associated with testosterone therapy. It also allowed for the establishment of normative ranges of serum testosterone levels on subcutaneous implant therapy. The study participants were 344 men who were accrued to an institutional review board-approved cohort study between April 2014 and 2017. Efficacy of the subcutaneous combination implant in maintaining low estradiol levels was evaluated. Serum levels of testosterone and estradiol were measured throughout the implant cycle, at week 4, and when symptoms returned. Correlations between patient demographics, dosing, and serum levels on therapy were evaluated. Mean testosterone dose was 1827 ± 262 mg. Mean anastrozole dose was 15.3 ± 3.2 mg with the majority of men receiving 16 mg of subcutaneous anastrozole. The mean interval of insertion was 4.8 months. Low estradiol levels were maintained throughout the implant cycle. Mean T level at week 4 was 1183 ± 315 ng/dl and 553 ± 239 ng/dl when symptoms returned. Levels of testosterone on therapy inversely correlated with body mass index. There were no adverse events attributed to testosterone or anastrozole therapy. Subcutaneous anastrozole delivered simultaneously with testosterone allowed for higher dosing of testosterone and less frequent intervals of insertion. Low-dose anastrozole released from the combination implant maintained low estradiol levels throughout the implant cycle and prevented clinical side effects attributed to excess estrogen.