Oral and Vaginal Misoprostol for Induction of Labor in Nulliparous Pregnant Women

Induction of labor is carried out for maternal and fetal indications and one of the most common indications is prolonged pregnancy. Recent studies have suggested that by continuing pregnancy beyond 41 weeks, there is statistically significantly higher perinatal morbidity and mortality as well as an increased risk to the mother. Thus, there is a growing body of evidence suggesting the elective induction of labor at 41 weeks of gestation instead of expectant management. Misoprostol, a prostaglandin E1 analog, is indicated for protection against gastric ulcers, but when administered prenatally it causes uterine contractions. Research exploiting this adverse effect has shown misoprostol to be superior to conventional methods for induction, resulting in shorter induction-to-delivery intervals, without any increase in adverse outcomes. It has the advantage of being cheap, stable at room temperature, and easy to be administered by various routes i.e., vaginal, oral, sublingual, or rectal. The differential outcomes of oral versus vaginal misoprostol may be secondary to different pharmacokinetics for oral compared with vaginal misoprostol. Oral misoprostol undergoes rapid absorption from the gastrointestinal tract and rapid and extensive de-esterification during first-pass metabolism to an active metabolite, misoprostol, peaking at 15 minutes with a half-life of 20-40 minutes. Misoprostol then undergoes early rapid elimination over 120 minutes, followed by slow elimination thereafter. The medication rapidly makes its way to the myometrium. ln contrast, after vaginal misoprostol administration, plasma concentration gradually increase, reaching a maximum level after 70-80 minutes before slowly being eliminated with plasma levels still detectable 6 hours after administration.