Hormone kinetics after intramuscular testosterone cypionate.

There have not been reports analyzing in detail the reproductive hormone changes in hypogonadal men after usual therapeutic injections of testosterone cypionate (TC). In 11 hypogonadal men 200 mg intramuscular TC caused a threefold rise in serum T (peak values, days 2 to 5), a 33% increase in % free T (%FT) (days 2 to 7), and a 4.5-fold rise of absolute FT (peak on days 2 to 3), a 66% increase in % nonsex hormone-binding globulin-bound T (%non-SHBG-T) (peak days 2 to 7), a sixfold increase in absolute non-SHBG-T (peak days 4 to 5), and a threefold rise of estradiol (days 2 to 7). Many of the men achieved androgen concentrations (T, FT, and non-SHBG-T) above the respective normal concentrations between days 2 and 7; then steroid values declined to basal levels by days 13 to 14. Non-SHBG-T showed the largest-fold absolute increase and on day 4 to day 5 averaged three times the mean in normal men. Five men achieved non-SHBG-T values several times the upper limit of our total normal range. Luteinizing hormone became suppressed in men receiving their first intramuscular TC injection and remained suppressed in men receiving chronic TC. Thus, in hypogonadal men, biweekly injections of 200 mg TC result in wide variations in circulating androgen levels, from high to elevated shortly after intramuscular TC declining to basal by days 13 to 14.