Comparison between oral and vaginal administration of misoprostol on uterine contractility

Objective: To compare the degree of absorption and the effect on uterine co ntractility of the prostaglandin E-1 analogue misoprostol after vaginal and oral administration. Methods: Thirty women with a normal intrauterine pregnancy between 8 and 11 weeks' gestation who requested termination of pregnancy were given either 0.2 mg (orally n = 5; vaginally n = 6) or 0.4 mg (orally n = 10; vaginally n = 9) of misoprostol. Intrauterine pressure was recorded using a Grass pol ygraph connected to a pressure transducer 30 minutes before misoprostol was given and for 4 hours thereafter. At the end of the recording, suction cur ettage was performed. Blood samples were obtained at 0, 0.5, 1, 2, 4, and 6 hours for measurement of misoprostol, which was assayed by high-pressure l iquid chromatography-mass spectrometry. Results: In all patients, the first effect was an increase in uterine tonus . After 0.4 mg of misoprostol administered orally, uterine tonus started to increase after a mean (+/- standard deviation) time of 7.8 +/- 3.0 minutes and reached its maximum after 25.5 +/- 5.0 minutes. The corresponding time s after vaginal administration were 20.9 +/- 5.3 minutes and 46.3 +/- 20.7 minutes, respectively. The initial increase in tonus was also more pronounc ed after oral than after vaginal administration. After vaginal administrati on, all patients developed uterine contractions; the activity, measured in Montevideo units, increased continuously during the observation period. Thi s was not the case after oral administration. Plasma levels of misoprostol were measured in 18 patients. The highest levels were found 30 minutes afte r oral treatment and 1-2 hours after vaginal administration. Conclusion: The long-lasting and continuously increasing uterine contractil ity after vaginal administration can be explained only in part by a direct effect of misoprostol. The longer period of elevated plasma levels of misop rostol may also have initiated the prolonged events leading to increased ut erine contractility. (Obstet Gynecol 1999;93:275-80. (C) 1999 by The Americ an College of Obstetricians and Gynecologists.).