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Types Of Replacement Therapy

Options for replacement include oral tablets and capsules, transdermal patches (scrotal and nonscrotal), and intramuscular injections. Older methyltestosterone oral formulations are undesirable because of their significant first-pass metabolism in the liver and significant liver toxicity. Testosterone undecenoate is absorbed through the lymphatic system and is thought to be free of liver toxicity (Nieschlag). Oral doses two or three times a day can reduce serum testosterone fluctuations, and may have a lower incidence of increased red cell mass in the blood and increased hematocrit.

Injectable testosterone is generally administered as a slow-release, oil-based preparation (testosterone enanthate or cypionate) that achieves supraphysiologic concentration approximately seventy-two hours after injection, then slowly declines over ten to fourteen days to a hypogonadal range. The wide fluctuation in levels during the dosing interval can produce enlarged breasts, breast tenderness, significant mood swings, and changes in libido and sexual function.

Transdermal patches have become available that provide a more physiologic approach to testosterone replacement by mimicking the normal diurnal variation in testosterone levels. The original patches were scrotal; more recently nonscrotal patches have become available (neither is currently available in Canada). Patches are applied at bedtime so that peak testosterone levels occur in the morning, then decline during the day (Nieschlag; Schow et al.). These patches appear to have most of the benefits of injected testosterone replacement. In addition there appears to be less aggressiveness, although these effects have not been studied in long-term trials (Morales et al.). Local dermatitis and higher costs have prevented their widespread use.

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