Mifepristone (RU 486) is an analogue of norethindrone with high affinity for progesterone receptors. It acts as a false
transmitter and blocks natural progesterone. It can effectively induce an abortion in an early gestation after a single oral
dose. The effectiveness is increased to approximately 95% by the addition of a low-dose prostaglandin analogue.
In France, where the drug has been used extensively, women with amenorrhea of less than 50 days and pregnancy
confirmed by serum b-hCG or ultrasonography receive an oral dose of mifepristone on day 1. On day 3, the patient
returns for prostaglandin (sulprostone or gemeprost) and D immune globulin if she is D negative. Patients remain in
the clinic for 4 hours, during which time expulsion of the pregnancy usually occurs. The patient then returns 8-15 days
later for measurement of b-hCG or ultrasonography. In more than 17,000 cases treated in France, complete abortion
was achieved in 95% of cases.

Failed abortion or excessive bleeding requires vacuum curettage. No serious complications or side effects have
occurred with mifepristone in this dosage. However, sulprostone, the prostaglandin E2 analogue used in Europe, has
been associated with myocardial infarction in three cases, resulting in one death. All three women were cigarette
smokers and were older than age 35. Misoprostol, the prostaglandin E1 analogue used with mifepristone in the United
States, has not been related to myocardial ischemia.
Another effective medical regimen for early abortion is the combination of the antifolate agent methotrexate with
misoprostol. Methotrexate is given as a single intramuscular dose followed 5-7 days later with vaginal misoprostol.
Efficacy appears to be slightly less than that observed with the mifepristone and misoprostol combination, and bleeding
may last longer. In the higher doses used to treat malignancy, methotrexate can have significant side effects, but these
are extremely rare with the low-dose regimen described above.

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