Differential effects of ibuprofen and naproxen sodium on menstrual prostaglandin release and on prostaglandin production in the rat uterine homogenate.

In two independent studies, ibuprofen and naproxen sodium were found to be equi-effective in alleviating dysmenorrheic symptoms. However, the effects of these drugs on menstrual PG release were found to be dissimilar. Ibuprofen primarily inhibited menstrual PGF2 alpha release with little effect on PGE2 release, whereas, naproxen sodium inhibited both PGF2 alpha and PGE2 release equally. To verify these results, we determined the inhibitory potency, IC50, of ibuprofen and naproxen sodium on PGF2 alpha and PGE2 synthesis in the rat uterine homogenate system. The preferential PGF2 alpha inhibitory activity of ibuprofen was confirmed. These findings suggest that ibuprofen may, in addition to inhibiting fatty acid cyclooxygenase, also inhibit PGF2 alpha reductase, or some other PG metabolic pathways which affect PGF2 alpha and PGE2 synthesis differently. The significance of this differential PG synthesis inhibitory effect in dysmenorrheic therapy is discussed.