Nebido® is the first registered testosterone undecanoate preparation for intramuscular injection. One ampoule contains 1000 mg of testosterone undecanoate in 4 ml of oily vehicle and is available in a corresponding individual packaging.
Nebido® is an intramuscularly administered depot preparation of testosterone undecanoate. Following intramuscular injection of testosterone undecanoate as an oily solution, the com-pound is gradually released from the depot and immediately cleaved by serum esterases into testosterone and undecanoic acid. An increase in serum levels of testosterone above basal values may be seen immediately after administration. The muscle serves as a depot for the sustained release of testosterone into the systemic circulation.
Circulating testosterone is chiefly bound in the serum to sex hormone-binding globulin (SHBG) and albumin. The albumin-bound fraction of testosterone easily dissociates from albumin and is presumed to be bioactive. The portion of testosterone bound to SHBG is not considered biologically active. The amount of SHBG in the serum and the total testosterone level will determine the ratio of bioactive and non-bioactive androgen. SHBG-binding capacity is high in prepubertal children, declines during puberty and adulthood, and increases again during the later decades of life. Approximately 60 % of testosterone in plasma is bound to SHBG, 2 % remains unbound (free) and the rest is bound to albumin and other proteins1.