Nebido is an intramuscular depot preparation containing testosterone undecanoate. For this reason, there is no first passage effect. After i / m injection of an oily solution of testosterone undecanoate, it is gradually released from the depot and is almost completely broken down by serum esterases into testosterone and undecanoic acid. An increase in serum testosterone concentrations relative to baseline values can be detected as early as the next day after injection.
Testosterone is responsible for the formation of male characteristics during intrauterine development, in early childhood, and also during puberty, and subsequently for the maintenance of the male phenotype and androgen-dependent functions (eg spermatogenesis, gonads). Insufficient secretion of testosterone leads to male hypogonadism, which is characterized by low serum testosterone concentrations. Symptoms associated with male hypogonadism include, but are not limited to, erectile dysfunction, decreased sex drive, fatigue, depressed moods, absence, underdevelopment, or regression of secondary sexual characteristics, and an increased risk of osteoporosis. Exogenous androgens are prescribed to increase inadequate endogenous testosterone levels and decrease symptoms of hypogonadism.