This study aimed to compare the change in levels of several laboratory values and the development of adverse events using two commonly used intramuscular testosterone therapy regimens. Men were included if they were 18 years or older and received one of the following testosterone therapy regimens: 100 mg intramuscular once weekly or 200 mg intramuscular once every other week. Primary outcomes were relative changes in total testosterone, free testosterone, estradiol, prostate-specific antigen, and hematocrit at 6 months after initiation of testosterone therapy. Secondary outcomes were any significant rises in estradiol, hematocrit, prostate-specific antigen, and any other treatment-related adverse events requiring cessation of testosterone therapy. A total of 263 men were enrolled. In a subanalysis of men who had a baseline hematocrit below 54% before intramuscular testosterone therapy initiation, we found the following: men who received 100 mg weekly injections were significantly less likely to have hematocrit levels rising above 54% (1/102 (1%) vs. 4/51 (8%); p = 0.023). No significant differences were recorded in the increase in total testosterone, free testosterone, prostate-specific antigen, and estradiol levels between both groups. A higher average serum testosterone over the dosing interval seen with the 200 mg regimen appears to be associated with a higher risk of erythrocytosis.
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