Buserelin. A review of its pharmacodynamic and pharmacokinetic properties, and clinical profile

The gonadotrophin releasing hormone (GnRH) [luteinising hormone-releasing hormone (LHRH); gonadorelin] agonist buserelin is a promising new agent in the treatment of a variety of disorders in gynaecology and andrology, paediatrics and oncology. While a single dose of buserelin stimulates the release of pituitary gonadotrophins, multiple doses produce reversible pituitary desensitisation, and this specific blockade of gonadotrophin support to the gonads provides the basis for the drug's efficacy in conditions dependent on sex hormone secretion. Thus, buserelin provides comparable efficacy to orchidectomy or high dose estrogens in the treatment of hormone-sensitive prostate cancer and exhibits a lower incidence of adverse effects. During the early phase of treatment it may be particularly useful in combination with antiandrogens. Buserelin also appears promising in hormone-sensitive premenopausal breast cancer. Extensive studies have proven the value of buserelin in endometriosis, where it produces a transient remission with gradual recurrence of the disease on cessation of treatment. Surgical intervention is necessary in severe disease after buserelin-induced involution of the lesions. In patients with uterine leiomyoma, preliminary data suggest that buserelin may be beneficial in rendering surgery more conservative by reducing fibroid size, although it appears unlikely to preclude surgical intervention. The use of buserelin to induce a state of reversible hypogonadotrophism before administration of exogenous gonadotrophins is a promising strategy in the treatment of infertility associated with polycystic ovary syndrome and other conditions of infertility with underlying ovarian dysfunction; such a strategy also clearly enhances the efficiency of in vitro fertilisation programmes. Initial studies suggest its potential usefulness as a female contraceptive when administered intermittently in conjunction with a progestogen. Buserelin represents a first-line treatment of central precocious puberty. In endometriosis the adverse effect profile of buserelin is generally favourable, with hypoestrogenic effects such as hot flushes and vaginal dryness, and decreased libido, predominating. There is no apparent detrimental effect on lipid metabolism. The potential for adverse hypoestrogenic effects on bone mineral content with long term administration remains to be clarified. Thus, the GnRH agonist buserelin represents an advance in the treatment of a variety of gynaecological and andrological as well as paediatric and oncological conditions, infertility and other sex-hormone dependent conditions, with a low incidence of adverse treatment effects.

Luteinizing hormone releasing hormone analogues for contraception

Peptide contraception based on LH-RH analogues is an interesting, fundamentally new lead to fertility control in women and men. A major advantage of using peptides instead of steroids for contraception is the fact that the hypothalamic peptides exert specific actions on the hypothalamic-pituitary-gonadal system and lack systemic effects. They are therefore less likely to cause metabolic derangements and other generalized adverse effects. Antagonistic analogues of LH-RH have been synthesized but until recently they have not been potent enough for clinical trials. However, chronic treatment with low doses of superactive stimulatory analogues of LH-RH paradoxically results in desensitization of the pituitary processes responsible for gonadotrophin release. This leads to a reversible inhibition of gonadal function. In women, ovulation can be inhibited by continuous intranasal LH-RH agonist treatment. In men, higher doses of LH-RH agonists have to be administered to suppress the gonadotrophin secretion enough to affect spermatogenesis. Optimal gonadotrophin suppression is, however, accompanied by a depression of the serum concentration of testosterone with loss of libido and impotence. The superagonists of LH-RH therefore have to be administered in combination with testosterone to induce oligo- or azoospermia without impotence. The overall results of clinical trials with superagonists of LH-RH for induction of inadequate corpus luteum function, luteolysis or early abortion in women are not impressive. The contraceptive effectiveness of these approaches to peptide contraception remains to be demonstrated in the human female. Inhibition of normal ovulation can, however, be consistently achieved by daily intranasal superagonist administration in women. This approach to fertility control has already been shown to provide safe and effective contraception in women.

From contraception to cancer: a review of the therapeutic applications of LHRH analogues as antitumor agents

LHRH and its analogues produce profound antireproductive effects in both sexes of a variety of animal species. Although the LHRH agonists induce gonadotropin release, gonadal steroid secretion, ovulation, and spermatogenesis as an expression of their traditional profertility pharmacologic profile, they paradoxically and characteristically cause predominant antifertility effects which have been extensively evaluated for potential contraceptive purposes. These agonists produce their antireproductive effects in both males and females by common mechanisms, ultimately resulting in disruption of pituitary-gonadal function, depression of steroidogenesis, and inhibition of target organs dependent on such gonadal support. Similar antireproductive effects have been observed with the LHRH antagonists which competitively inhibit LHRH-induced gonadotropin secretion resulting in reduced blood gonadal steroid levels. Use of the inhibitory properties has been extended to cancer therapy based on the ability of the LHRH analogues (particularly the agonists) to inhibit the growth of steroid-dependent (responsive) tumors (e.g., mammary, prostate) similar to that produced by gonadectomy and antisteroid treatments. The use of these peptides for selected hormone-sensitive tumors presents a novel pharmacotherapeutic application for this class of drug.