Buccal Absorption of Testosterone and Its Esters Using a Bioadhesive Tablet in Dogs

Purpose. As the oral bioavailability of testosterone is very low because of its high first pass effect, buccal administration might present a viable alternative. In this study a buccal bioadhesive tablet was used in order to sustain the delivery and bypass the liver. Methods. Testosterone and testosterone acetate, propionate, enanthate and decanoate were investigated. The influence of the concentration of testosterone (10–50%) and testosterone esters (30%) on in vitro bioadhesion was investigated. The absolute (IV) and relative (oral) bioavailability of 60 mg testosterone or an equivalent amount of testosterone ester was determined in castrated male dogs. Results. Both the in vitro detachment force and the work of adhesion decreased gradually with an increasing amount of testosterone and for an increasing chain length of the esters, except in the case of testosterone enanthate. The in vivo results revealed that the bioavailability of testosterone was significantly higher (p < 0.05) than that of the esters, which is probably due to the lower solubility of the esters. The mean absolute bioavailability of testosterone from the bioadhesive tablet was 14.1%, while the mean relative bioavailability was 1370%. The buccal administration of testosterone via the bioadhesive tablet allowed the maintenance of the plasma level at above 3 ng/ml for 15 to 24 h. Conclusions. Buccal absorption of testosterone was significantly higher than that of its esters.