The antagonism by anti-inflammatory analgesics of prostaglandin f 2 alpha-induced contractions of human and rabbit myometrium in vitro.

The anti-inflammatory analgesic drugs, aspirin, indomethacin, phenylbutazone, mefenamic acid ibuprofen and flurbiprofen are shown to inhibit in a dose-dependent manner the force of contraction of isolated human pregnant myometrial strips which have been stimulated to contract by adding prostaglandin (PG) F2alpha to the tissue bath. These drugs and also flufenamic acid and salicin show a similar antagonism of the action of PGF2alpha with isolated rabbit non-pregnant myometrium. The ratio of the inhibitory concentration in vitro to the maximum plasma level after a normal dose in vivo suggests that phenylbutazone and possibly ibuprofen may be capable of inhibiting human uterine contractions in vivo. Patients who were treated with aspirin during induction of abortion using PGF2alpha during the second trimester of pregnancy showed no significant change in the induction-abortion interval compared with patients not taking aspirin.