Vaginal administration of PGE2 for induction of labor stimulates endogenous PGF2 alpha production.

Prostaglandin E2 is effective for induction of labor but many preparations exist using a variety of vehicles from which the active ingredient may not be equally available. Plasma concentrations of bicyclic PGE2 metabolite (PGEM) and 13, 14-dihydro, 15-keto PGF2 alpha (PGFM) were measured following administration of a 3mg PGE2 vaginal tablet or 1mg PGE2 vaginal gel to twenty-four parous women with favorable induction features, randomly allocated to receive one or other preparation. PGEM increased rapidly following both administration of the 3mg PGE2 vaginal tablet and the 1mg PGE2 vaginal gel, reaching a peak within 40 minutes of PGE2 administration. The maximal rise in PGEM in the gel group correlated directly with the change in cervical score and inversely with the need for augmentation with oxytocin and the induction-delivery interval. A secondary rise in PGFM was noted in both groups 3-4 hours following PGE2 administration. The magnitude of the increase in PGE2 may be important in the clinical response to PGE2 administration, while PGE2 absorption may switch-on endogenous PGF2 alpha production, similar to what is seen in spontaneous labor.