Nafarelin. A review of its pharmacodynamic and pharmacokinetic properties, and clinical potential in sex hormone-related conditions.

Nafarelin, a synthetic agonist of gonadotrophin-releasing hormone (GnRH) [luteinising hormone-releasing hormone (LH-RH); gonadorelin] appears likely to join the other GnRH analogues currently used in a range of conditions reliant on gonadotrophins or sex hormones. With repeated administration, the pituitary becomes desensitised, and gonadotrophin release, and therefore sex hormone synthesis, are inhibited. Nafarelin has proved to be comparable to danazol in the management of women with endometriosis, with fewer potentially harmful adverse effects. Nafarelin has also been used effectively in in vitro fertilisation programmes, and in hirsute women and those with uterine leiomyoma, particularly to induce preoperative fibroid shrinkage. The drug shrinks hypertrophic tissue in men with benign prostatic hyperplasia, although treatment would need to be maintained indefinitely and therefore should probably be reserved for those unsuitable for prostatectomy. Preliminary data suggest that nafarelin is equivalent to diethylstilbestrol (stilboestrol) in terms of disease-free survival in men with prostate cancer. As a reliable method of contraception, nafarelin gives unpredictable results in men and the promising results in women may be offset by hypoestrogenic side effects. Nafarelin may join other GnRH agonists which are now routinely used in the management of children with central or combined precocious puberty. Nafarelin is readily and rapidly absorbed following intranasal delivery, and is protected to some extent from enzymatic degradation. The resultant relatively long elimination half-life allows once- or twice-daily administration. Estrogen depletion accounts for the most common side effects associated with nafarelin, including hot flushes and vaginal dryness, which are mild and tolerable in most patients. Reversible resorption of trabecular bone can occur during nafarelin therapy, perhaps necessitating cyclical treatment to enable bone mass to recover. Nafarelin, therefore, looks likely to find a role in the treatment of women with endometriosis, and results achieved in other conditions dependent on the pituitary-gonadal axis are promising.