Application site affects the pharmacokinetics of topical testosterone applied to the axilla compared with the inner arm.

Purpose: This study compared the pharmacokinetics of a single dose of 1% testosterone solution after application to the inner arm or the axilla as application sites for transdermal testosterone therapy.

Methods: Healthy, not pregnant, premenopausal women, 18 to 45 years of age with a body mass index of 20 to 28 kg/m(2) were enrolled into a single-center, open-label, randomized, 2-way crossover study. Serum total testosterone (TT), free testosterone (fT), and sex hormone binding globulin concentrations were measured. Pharmacokinetic parameters determined from serum TT and fT included area under the serum concentration versus time curve from time zero (pre-dose) until 72 hours post-dose (AUC0-72), Cmax, and Tmax. Descriptive statistics were performed on serum concentrations of TT and fT for each site. ANOVA was performed on AUC0-72 and Cmax.

Findings: A single-dose application of 1% testosterone solution to the inner arm and the axilla produced clear increases in TT and fT. Slower and lower increases in TT and fT were observed after treatment to the inner arm. Based on baseline-corrected AUC versus time curves, the bioavailability of 1% testosterone solution was increased 2-fold for the axilla compared with the inner arm.

Implications: The absorption of a 1% testosterone solution was significantly greater after application to the axilla than to the inner arm. Study number DDS16; Australian Therapeutic Goods Administration, CTN 2005/158.