Utility of a single serum testosterone measurement to determine response to topical testosterone replacement in hypogonadal men.

OBJECTIVE

To evaluate the utility of single serum testosterone measurement in patients receiving transdermal testosterone therapy.

RESEARCH DESIGN AND

METHODS

Data were from an open-label, 120 day, multi-center titration trial in androgen-deficient men receiving an initial daily dose of 60 mg testosterone (testosterone topical solution 2%) applied to axillae (30 mg/axilla). Average concentration (Cavg) of serum testosterone (TT) was determined on days 15, 60, and 120; doses were adjusted to maintain normal Cavg (300-1050 ng/dL [10.4-36.4 nmol/L]). Accuracy of single serum TT measurements (2, 4, 8, 12, 16, and 20 hours post-dose) was assessed in patients with Cavg TT within and below (<300 ng/dL [<10.4 nmol/L]) the normal range.

CLINICAL TRIAL REGISTRATION: Clinicaltrials.gov - NCT00702650.

MAIN OUTCOME MEASURE: Serum testosterone levels.

RESULTS

In patients with normal Cavg (n = 85), 79% to 92% had serum testosterone levels within normal range 2, 4, 8, 12, 16, and 20 hours post-dose; significant effects of time post-dose for single testosterone measurement accuracy (P = 0.01) were observed: testing accuracy peaked 4-8 hours post-dose and tapered ∼16 hours post-dose. In 28/63 instances with low Cavg TT throughout the study a normal 2 hour serum TT level was observed. The average percentage (across all days) of discordant results between Cavg (<300 ng/dL [<10.4 nmol/L]) and single serum TT measurements (300-1050 ng/dL [10.4-36.4 nmol/L]) declined with increasing time from dose application (44% at 2 hours, 38% at 4 hours, 22% at 8 hours, 3% at 16 hours).

CONCLUSIONS

Reliance on a single serum testosterone measurement to determine the need for dose adjustment of testosterone topical solution 2% may lead clinicians to change the dose unnecessarily, or alternatively, not increase the dose when necessary. The results reported here are limited to testosterone topical solution 2% and may not be applicable to other topical agents.