Clomifene is a selective estrogen receptor modulator (SERM) that increases production of gonadotropins by inhibiting negative feedback on the hypothalamus. This synthetic drug comes supplied as white, round tablets in 50 mg strength only. It has become the most widely prescribed of all fertility drugs. It is used in the form of its citrate to induce ovulation. Clomifene inhibits estrogen receptors in hypothalamus, inhibiting negative feedback of estrogen on gonadotropin release, leading to up-regulation of the hypothalamic–pituitary–gonadal axis. Zuclomifene, a more active isomer, stays bound for long periods of time. In normal physiologic female hormonal cycling, at 7 days past ovulation, high levels of estrogen and progesterone produced from the corpus luteum inhibit GnRH, FSH and LH at the hypothalamus and anterior pituitary.
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