The pharmacokinetics of the prostaglandin E1 analogue misoprostol in plasma and colostrum after postpartum oral administration

Objective: To study pharmacokinetics of prostaglandin El analogue, misoprostol in plasma and colostrum after postpartum oral administration. Study design: Twenty women received 600 mug doses of misoprostol orally after delivery. Plasma levels of the principal metabolite, misoprostol acid, were measured at 2, 10, 20, 30, 40, 50, 60, 90, 120, 180, 240 and 300 min (48 samples). Colostrum was expressed from the breasts to measure misoprostol acid at 60, 120, 180, 240, and 300 min (24 samples). Assay was done using isotope dilution gas chromatography (GC)/negative ion chemical ionisation mass spectrometry (MS). Results: The plasma concentration of misoprostol acid rose quickly. Two minutes after oral administration its mean level was 91.5 pg/ml, peaked at 20 min (344 pg/ml), then fell steeply by 120 min (27.8 pg/ml) and remained low for the duration of the study. Misoprostol acid in colostrum reached maximum concentration of 20.9 pg/m within 1 h after oral administration. It then declined gradually to 17.8 pg/ml at 2 h, 2.8 pg/ml at 4 h and to <1 pg/ml at 5 h. Areas under misoprostol concentration versus time curves up to 5 It were 290.1 pg h/ml in the plasma and 51.4 pg h/ml in colostrum, respectively. Conclusion: Misoprostol acid is secreted in colostrum within 1 h of oral administration of 600 mug of misoprostol; the pharmacokinetics of misoprostol after oral administration during postpartum is similar to that of other pregnancy periods. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.