Anti-progesterones for the interruption of pregnancy

Therapeutic abortion can be performed effectively and safely by vacuum aspiration of the uterus up to 12 weeks of amenorrhoea. Although the operative procedure could be regarded as simple, complications do occur and attempts have been made to develop non-surgical means of terminating pregnancy in the first 3-4 weeks following the first missed menstrual period. A variety of PG analogues have been developed which induce abortion in over 90% of women when given by vaginal pessary or intramuscular injections (see Bygdeman, 1984). In a large multicentre study (WHO, 1987) 0.5 mg sulprostone, administered three times with 3 h intervals, was recently found to be equally as effective as vacuum aspiration for termination of early pregnancy. The frequencies of complete abortion were 91 and 94%, respectively. However, the widespread acceptance of PG treatment is limited by a relatively high incidence of gastrointestinal side-effects and uterine pain. Treatment with antiprogesterones, both mifepristone and epostane, effectively induces abortion during early pregnancy, but the frequency of complete abortion is too low to be clinically acceptable. It remains to be demonstrated if other antiprogesterones such as ZK 98.734 and ZK 98.299, currently under development, may change this conclusion. Administration of mifepristone induces uterine contractions and increases the sensitivity of the myometrium to prostaglandins. These effects allowed the development of sequential treatment with a low dose of mifepristone and PG analogues administered vaginally or intramuscularly. The combined therapy has been shown to be highly effective (frequency of complete abortion between 95 and 100%) and is seemingly associated with a lower frequency of side-effects than if PG analogues are used alone. Whether this medical abortion method will be a realistic alternative to vacuum aspiration during the first 8 weeks of pregnancy depends on the outcome of further clinical trials, including randomized studies comparing the two procedures. It has been shown that mifepristone crosses the placenta (Frydman et al, 1985). An important factor which needs to be verified in future studies is therefore the possible embryotoxicity of this type of compound. The risk that pregnancy continues in spite of treatment can never be excluded.(ABSTRACT TRUNCATED AT 400 WORDS)