Transdermal testosterone therapy in the treatment of male hypogonadism.

Five hypogonadal men were treated with transdermal testosterone therapy, using a testosterone patch applied to the scrotal skin. Daily application of the patch, which contained 10 mg testosterone, produced an increase in serum testosterone concentrations from a pretreatment value of 45 +/- 12 (+/- SE; 1.5 +/- 0.4) to 436 +/- 80 ng/dL (15.1 +/- 2.8 nmol/L; P less than 0.001) after 4 weeks of treatment. Normal serum testosterone concentrations were achieved in all men after 6-8 weeks of therapy and were maintained during continued long term therapy for 9-12 months with a patch containing 15 mg testosterone. All men reported a subjective increase in libido and sexual function during therapy, and three men preferred it to testosterone injections. The serum testosterone and estradiol levels did not rise above the normal adult male range at any time during therapy. However, elevated serum dihydrotestosterone (DHT) concentrations occurred during treatment; the pretreatment DHT concentration was 95 +/- 3 ng/dL (3.3 +/- 0.1 nmol/L), and it increased to 228 +/- 40 ng/dL (7.8 +/- 1.4 nmol/L) after 4 weeks of treatment and remained elevated thereafter. The individual mean DHT to testosterone ratio increased from a pretreatment value of 0.2 (range, 0.1-0.3) to 0.6 (range, 0.4-0.7) after 2 weeks of therapy and remained high thereafter. Comparison of the serum DHT levels in patients during therapy with those in normal men who had similar testosterone concentrations [531 +/- 62 vs. 566 +/- 72 ng/dL (18.4 +/- 2.1 vs. 19.6 +/- 2.5 nmol/L); P greater than 0.05] revealed that the mean serum DHT concentration was significantly higher in the patients [315 +/- 69 vs. 87 +/- 6 ng/dL (10.8 +/- 2.4 vs. 2.9 +/- 0.2 nmol/L); P less than 0.001], as was the mean DHT to testosterone ratio [0.6 (range, 0.25- 1.1) vs. 0.16 (range, 0.09- 0.24); P less than 0.001]. The high serum DHT levels presumably were due to increased metabolism of testosterone to DHT by the 5 alpha-reductase in the scrotal skin. Serum 3 alpha-androstanediol glucuronide levels were not elevated in the patients. We conclude that transdermal testosterone therapy is an effective long term treatment for hypogonadism in men. It is, however, associated with high serum DHT levels, whose potential long term effects on the prostate and other tissues need to be investigated.