A comparative permeation/release study of different testosterone gel formulations

The major indication for testosterone (T) treatment is male hypogonadism that is characterized by low serum T concentrations. Although a recently developed hydroalcoholic gel, Androgel®, containing 1% T addresses many of the problems associated with the more conventional formulations, the bioavailability of T is only 10% requiring 5 to 10 g of gel to be applied daily. The present study was performed to investigate the effect of isopropyl alcohol (IPA) content as a penetration enhancer based on its ability to prevent skin dryness and in turn to increase T permeation from hydroalcoholic gels. Five different hydroalcoholic gel formulations, containing 1% T and carbopol as the gel-forming polymer, were formulated by varying the amount of IPA. The release of T from each gel, including Androgel®, was studied in vitro on Franz diffusion cells using cellulose ester and Celgard® 2400 as synthetic membranes and hairless guinea pig skin as a natural membrane. The amount of drug released from the gels was analyzed using an HPLC-UV method. The results of release/permeation studies on guinea pig skin showed that all the gels were similar to Androgel®, indicating that the addition of IPA does not affect the release of T from hydroalcoholic gels. Although no statistical significant difference was seen, the release profiles of the gels showed a trend of increasing release of T with increasing concentration of IPA. Thus, IPA does have a potential to increase the bioavailability of T from hydroalcoholic gels.