Testosterone Therapy: Injectable Androgens

Abstract

Testosterone formulations have been available to patients since the 1930s, but have proven less than ideal. Conventional injectable testosterone esters are being used as testosterone replacement, but generate supraphysiological testosterone concentrations shortly after injection followed by a rapid decline, becoming subphysiological in the days before the next injection. These rapid fluctuations in plasma testosterone are subjectively experienced as disagreeable. Available since 2004, testosterone undecanoate is an injectable testosterone preparation with a considerably better pharmacokinetic profile. After two initial injections with a 6-week interval, the future intervals between injections are usually 12 weeks, amounting to a total of four injections per year. Plasma testosterone concentrations with this preparation are nearly always in the range of normal men, so are its metabolic products estradiol and dihydrotestosterone. Testosterone undecanoate, like other testosterone preparations, reverses the effects of hypogonadism on bone and muscle and significantly improves metabolic parameters and sexual functions, without the “roller coaster” effects of traditional testosterone injections. Other adverse effects, such as polycythemia and disturbed lipid profiles, have not been observed. Although some studies suggest a link between injectable testosterone and comorbidities such as prostate cancer, diabetes, and cardiovascular disease, conflicting data highlight the need for longer-term better controlled, randomized studies. Although testosterone undecanoate stands out as a valuable contribution to the treatment options of androgen deficiency, a number of alternative therapies such as selective androgen receptor modulators are under development proving, from preliminary studies, as competitive testosterone replacement options.