ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2008) 16 P115

The influence of application site on testosterone serum concentrations after transdermal testosterone gel

Sebastian Neggers, Richard Feelders, Maarten van Aken, Wouter de Herder, Aart-Jan van der Lely & Frank de Jong

Erasmus University Medical Centre Rotterdam, Rotterdam, The Netherlands.

Background: Testosterone (T) in a hydroalcoholic gel is commonly prescribed as androgen replacement therapy and may not be accompanied by peaks and troughs of serum T levels as seen in T-injectables. We assessed in 17 subjects the differences in serum testosterone (sT) and free T (fT) levels during four different application periods.

Methods: Patients where on daily 50 mg Androgel®, for 7 consecutive days in each cycle, on day 8 serum was sampled from both antecubital veins at 9.00 pm. Period 1 started with application at both shoulders and right upper arm up to 10 cm from the elbow pit. Period 2 was equivalent to period 1 except that T-gel was applied to the left arm. Period 3 was similar to the second except T-gel was applied up to the left elbow pit. Period 4, T-gel was solely applied on the abdomen.

Results: No significant differences in (free) T levels were observed between regimens 1 and 2. However, in period 3 sT and fT levels (median±S.D.) sampled from the left arm were higher compared to the right arm (sT left 15.60±22.17 nmol/l, right 12.20±4.70 nmol/l, P=0.011; fT left 0.39±0.74 nmol/l, right 0.29±0.15 nmol/l P=0.012). Significant lower sT (7.35±3.45 nmol/l, P<0.05) and fT (0.16±0.08 nmol/l, P<0.05) were observed when T-gel was applied to the abdomen compared to all other applications.

Conclusion: Peaks of sT concentrations are observed during T-gel therapy with different application regimens. Serum sampling within the T application area may reveal high T levels, possibly due to local T-accumulation. This should be taken into account with interpretation of sT levels and dose titration during transdermal androgen substitution. Efficacy of T application at the shoulders may be higher compared to application at the abdomen.

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