Transdermal testosterone: 40% less bioavailable on abdomen


Transdermal testosterone: 40% less bioavailable on abdomen
by Anthony Roberts

A recent study suggests that men using testosterone gel should apply it to the shoulders/arms. Applying testosterone gel to the abdomen resulted in 30-40% less bioavailability, although it should be noted that application in either spot resulted in acceptable testosterone levels (i.e. both raised the hypogonadal user into the eugonadal range). Interestingly, and counterintuitively to me, serum estrogen and dihydrotestosterone exactly followed the dose response curve of the testosterone. Bodyfat is rich in aromatase, the enzyme responsible for conversion of testosterone into estrogen, so logically, we’d assume applying testosterone gel to the abdomen would result in higher plasma estrogen when compared to applying it to the arms and shoulders.

But that’s not what happened…

Another interesting fact from this study is that the highest testosterone levels achieved by the subjects was roughly similar to the level I got from 100mgs/eod of testosterone propionate (injectable). So, if you’re a guy who’s scared of needles, transdermal testosterone gel, applied directly to the arms and shoulders, may be a viable option. Another option would be to apply the gel directly to your vagina.

Pharmacokinetics and Relative Bioavailability of Testosterone Absorption After Administration of a 1.62% Testosterone Gel to Different Application Sites in Hypogonadal Males

Abstract

Objective: To determine the pharmacokinetics, bioavailability, and safety of a new formulation (1.62%) of testosterone gel that produces eugonadal testosterone levels using a lower amount of gel than the currently available 1% gels. The new gel was applied to different skin application sites in hypogonadal males.

Methods: In an open-label, randomized, three-way crossover study, 36 subjects applied 5 g of 1.62% testosterone gel (81 mg testosterone) once daily to the abdomen, upper arms/shoulders, or alternating between both locations per a set schedule for 7 days. Serum levels of testosterone, dihydrotestosterone, and estradiol were measured and used to compare the pharmacokinetics and bioavailability of the three treatments.

Results: Each application method produced average testosterone concentrations within the eugonadal range (300-1000 ng/dL) and steady-state testosterone concentrations were achieved after two days of gel application to either the abdomen or upper arms/shoulders. When gel was applied to the abdomen approximately 30%-40% lower bioavailability (AUC0-24) was observed compared to upper arms/shoulders application. The 1.62% testosterone gel was found to be safe and well tolerated in hypogonadal males.

Conclusions: Although lower testosterone bioavailability was observed after abdominal application of 1.62% testosterone gel compared to upper arm/shoulders application, application to either site provided eugonadal levels of testosterone.

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