Advances in testosterone replacement therapy.

The major goal of androgen substitution is to replace testosterone at levels as close to physiological concentrations as is possible. The mainstay of testosterone susbstitution are parenteral testosterone esters (enanthate and cypionate) to be administered every 2-3 weeks. A major disadvantage is the strongly fluctuating levels of plasma testosterone which are at least 50% of the time not in the physiological range. A significant improvement is parenteral testosterone undecanoate producing normal plasma testosterone for 12 weeks. Subcutaneous testosterone implants provide the patient, depending on the dose of implants, with normal plasma testosterone for 3-6 months. Its use is, however, not widespread. Oral testosterone undecanoate dissolved in oil bypasses the liver via its lymphatic absorption, but resulting plasma levels are erratic. Transdermal testosterone preparations have already been available for two decades. Transdermal testosterone gel produces attractive pharmocokinetic serum testosterone profiles and offers greater flexibility in dosing. Transdermal gel has been recommended in elderly males. In case of complications its use can be discontinued immediately. Oromucosal testosterone preparations are being developed. Testosterone replacement is usually of long duration, and patient compliance is of utmost importance. Therefore, the patient must be involved in the selection of the type of testosterone preparation.