Pharmacokinetics of follicle-stimulating hormone: clinical significance

To review studies that examine the pharmacokinetics and pharmacodynamics of endogenous, as well as several exogenous FSH preparations.

Related studies were identified through a computerized bibliographic search.

Initial pharmacodynamic studies were done in animal models and in women and men with either hypogonadotropic hypogonadism or suppressed hypothalamic-pituitary-gonadal axis. More recent studies evaluated FSH pharmacokinetics during ovulation induction treatment in women with normal ovulatory cycles or polycystic ovarian syndrome.

Various types of FSH exist according to their sialic acid content. High estrogen levels induce the secretion of less sialylated molecules with higher receptor affinity and an increased clearance rate. It appears that there is a threshold FSH level that should be reached to achieve an ovarian response. A very narrow range exists between the threshold and ceiling level for monofollicular growth. This threshold level is surpassed intentionally during IVF treatment cycles to induce multiple follicular recruitment. The threshold level can change under situations such as polycystic ovaries, perimenopause, oral contraceptives, and GnRH analogue treatment.

To avoid the risk of ovarian hyperstimulation syndrome and multiple pregnancies, careful adjustments of serum FSH levels should be made by fine dosage modifications. By monitoring FSH levels and using less sialylated preparations, the efficacy of the treatment probably will improve.