BIO AND IMMUNO‐ACTIVITY OF FSH IN SERUM AFTER INTRAMUSCULAR INJECTION OF HIGHLY PURIFIED URINARY HUMAN FSH IN NORMAL MEN

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Abstract
SUMMARY: The pharmacokinetics of a human FSH preparation widely used in clinical practice was evaluated in healthy male volunteers whose endogenous FSH was suppressed by 19‐nortestosterone injections. 9‐7 h following intramuscular injection of 150 IU FSH the mean immunoreactive peak concentration over baseline was 3–8 IU/1. Injection of 450 IU FSH led to a mean immunoreactive peak level of 10‐4 IU/1 at 9‐8 h. Mean half‐life was 24‐6 h (150 IU FSH) and 36‐2 h (450 IU FSH). Serum bioFSH concentrations were suppressed below the detection limit after injection of the 19‐nortestosterone and rose to preinjection levels after administration of FSH. Mean bioactive peak level for the 450 IU FSH was 7‐3 IU/1 FSH at 7‐4 h. The half‐life of bioFSH was calculated to be 13‐4 h and is considerably shorter than the half‐life of immunoFSH. Serum inhibin levels were suppressed by 19‐nortestosterone and did not change significantly after injection of the FSH preparation, suggesting that the FSH dose was insufficient to elicit this biological response. It is concluded that the currently used dose regimen for the treatment of male hypogonadism is inadequate for maintenace of serum bioFSH levels in the normal range.