Plasma androgen levels in men after oral administration of testosterone or testosterone undecanoate.

Plasma testosterone and androstenedione levels in men were measured after oral administration of free testosterone and testosterone undecanoate. Both androgens were determined by simultaneous, specific radioimmunoassays after separation and isolation by thin layer chromatography. While free unesterified testosterone had no effect on plasma androgen levels, a striking increase of both testosterone and androstenedione levels was noted after administration of testosterone undecanoate, which is otherwise only achieved by parenteral testosterone application. This effect of testosterone undecanoate is probably due to absorption via the lymph rather than via the portal vessels so that peripheral circulation is reached before metabolism in the liver. Testosterone undecanoate promises to be an effective medication for oral androgen replacement.