Transdermal testosterone gel: pharmacokinetics, efficacy of dosing and application site in hypogonadal men

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Abstract
Testosterone gels are being increasingly used throughout the world. There is still some controversy associated with their use, but many of the uncertainties are gradually being overcome and explained. The authors from the USA evaluated the pharmacokinetics and the efficacy of dosing and application sites of another such transdermal gel. The arrival of oral agents for treating male erectile dysfunction has made it easier for GPs to treat this condition. The authors from Southampton have examined the safety of sildenafil used in general medical practice in England, finding that it was used safely at this level, with no unexpected events. OBJECTIVE: To determine the regimen that would most effectively maintain serum testosterone concentrations in treated hypogonadal men within the normal reference range of 3–11.4 µg/L. PATIENTS AND METHODS: Eighteen men aged 24–69 years with either primary or secondary hypogonadism participated in and 16 completed a randomized, six‐treatment regimen, three‐period (phase), three‐way matrix‐type crossover study. A 1% and 2% testosterone gel (CP601, Cellegy Pharmaceuticals, Inc., San Francisco, USA) was administered either once or twice daily transdermally at different body sites to determine optimal dosing, application sites, and its pharmacokinetics and tolerability in hypogonadal men. Treatments A–F included 1 g of 1% and 2% gel that was equivalent to 10 or 20 mg of testosterone, applied once or twice daily to the skin of either the thigh or the upper arm. Six men also participated in a study of 3 g of 2% gel that was equivalent to 60 mg of testosterone applied once daily, half on each thigh. Pharmacokinetic variables were calculated for testosterone for each man in each treatment period and the results analysed by anova . RESULTS: In general the higher dose regimens produced higher serum concentrations of testosterone; the 3 g/2% dose was most successful in maintaining serum testosterone within the normal reference range. The average testosterone concentration (C avg ) was 6.52 µg/L and all men had a C avg of > 3.0 µg/L. The prediction of all men achieving a C avg of > 3.0 µg/L was 96%. The mean minimum concentration (C min ) was 3.83 µg/L and half the patients had a C min of > 3.0 µg/L. Most men had serum testosterone levels within the normal reference range throughout the 24 h, and the treatment was well tolerated. CONCLUSIONS: The 3 g/2% dose applied to the skin daily resulted in serum testosterone in the normal reference range in most hypogonadal men. Dose adjustments to either a lower or higher dose should shift serum testosterone concentration to the desired range in those who do not achieve this range with this dose.

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