Anti-oestrogen therapy

Anti-oestrogens induce gonadotrophin release by occupying hypothalamic oestrogen receptors and so interfering with oestrogen feedback.

Clomiphene citrate induces ovulation in 65-80% of patients and is associated with a pregnancy rate of 50-60% following up to 6 cycles of treatment (1). Multiple pregnancy occurs in about 6% of patients and the rate of miscarriage may be slightly increased. There is a tendency to increase LH secretion in PCOS.

In general anti-oestrogen treatment e.g. clomifene, should not be initiated in primary care (2):

• the need for monitoring with ultrasound (at least in the first cycle of treatment) and serum endocrine tests means that, in general, clomifene should not be started in general practice
• however, it is possible for GPs to continue to prescribe clomifene after the appropriate dose has been established; this should be done as part of a formal shared-care agreement between hospital and primary care.

Other anti-oestrogens include tamoxifen which has a similar structure and mode of action to clomifene and one of its licensed uses is for the treatment of anovulatory infertility. However, it is rarely used in this way, with its place being limited to treating women who experience troublesome unwanted effects with clomifene.

Reference:

1. Kousta E et al (1997). Modern use of clomiphene citrate in induction of ovulation. Hum Reprod Update, 3, 359-65.
2. Drug and Therapeutics Bulletin (2004); 42 (4): 28-32.