Hormonal Mifepristone

Synthetic hormones mifepristone and Plan B, drugs that prevent pregnancy (Section 11.4)... 

As so often happens in the hormonal field, drugs of this class have commonly been given in excessive doses, no doubt because of the over-riding need to ensure efficacy as time goes by lower doses are proving effective and are better tolerated. For emergency contraception, for example, mifepristone 10 mg now appears to be as effective as the 25 mg that was recommended before (12). 

RU486 (= Mifepristone)] Nobel Prize, Chemistry, 1939, sex hormones, acceptance forbidden by Nazis) Synthetic PROG-R antagonist [early... 

Figure 13.3. Stmctures of the gestagene steroid hormone progesterone, and the progesterone receptor antagonist mifepristone...

The antiprogesterone mifepristone, almost exclusively used as an abortifacient, has also been tried as a post-coital contraceptive (11). In one randomized comparative trial, a single dose of mifepristone 600 mg was at least as effective as the usual hormonal method (12). Women who took mifepristone had lower rates of adverse effects, particularly nausea and vomiting, but their next menstrual period was more likely to be delayed. In another randomized trial, both methods were equally effective (SEDA-16, 466). The use of an estrogen + a progestogen had a higher total incidence... 

Structures of steroids used as oral contraceptives. (A) Combination pills containing an estrogen -P progestin. (B) The progestin-only pill. (C) RU-486 or mifepristone, which can be utilized as an abortifacient. [Reproduced with permission from S. W. Norman and G. Litwack, Hormones, 2nd ed. San Diego Academic Press, 1997]. 

A small clinical study comprising 30 women was conducted with Proellex and has appeared in the manufacturer s web site, but to date not in a peer-reviewed journal (http //www.reprosrx.com). Doses of 12.5, 25 and 50 mg were compared to 3.75 mg of the gonadotropin-releasing hormone (GnRH) superagonist, Lupron . There was also a placebo group. The response was similar to what had been reported with mifepristone and asoprisnil. 

Other strategies are based on the observation that mifepristone can retard endometrial development. In two studies, a total of 53 women received 200 mg mifepristone 48 h after the luteinizing hormone (LH) surge and there were only three pregnancies in a total of 335 cycles [83, 84]. In view of its complexity, a method dependent on the precise timing of the LH surge does not represent a practical approach to contraception. 

Escudero, E.L., Boerrigter, P.J., Bennink, H.J., Epifanio, R., Horcajadas, J.A., Olivennes, F., Pellicer, A. and Simon, C. (2005) Mifepristone is an effective oral alternative for the prevention of premature luteinizing hormone surges and for premature luteinization in women undergoing controlled ovarian hyperstimulation for in vitro fertilization. Journal of Clinical Endocrinology and Metabolism, 90, 2081-2088... 

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