Plasma prostaglandin E2 metabolite levels during labor induction with a sustained-release prostaglandin E2 vaginal insert

OBJECTIVE: To measure prostaglandin E-2 levels during labor induction with a sustained-release vaginal polymer insert (prostaglandin E-2 insert) and to determine whether Bishop score change correlated with tachysystole. METHODS: Twelve primiparas and 12 multiparas were treated with a 0.3 mg per hour sustained-release polymer vaginal prostaglandin E-2 insert for up to 24 hours. Bishop score was assessed at start and old of therapy, and serum samples were collected at 4-hour intervals. Prostaglandin E-2 metabolite (PGEM) levels were measured by specific enzyme immunoassay. RESULTS: Exposure averaged 13.5 +/- 7.2 hours. Four patients (16.7%, three nulliparas) had tachysystole. Mean PGEM levels increased from 187 +/- 42 pg/mL at baseline to 548 +/- 110 pg/mL at 12 hours (P <.05) and remained relatively stable thereafter. Nulliparas with Bishop score changes of four points or more had the highest increase, with average peak levels of 985 +/- 109 pg/mL, compared with 452 +/- 58 pg/mL for all others (P <.001. Patients with tachysystole had higher 4-hour (P<.01) and overall (P <.04) increases in PGEM level. Removal of the insert led to an average decrease of 335 pg/mL in PGEM levels (P <.01). The decrease correlated with the PGEM level measured before removal (r =.94, P <.0001) and the maximum PGEM increase from baseline (r =.94, P <.0001). The mean mixed venous cord PGEM level was 409 +/- 375 pg/mL. CONCLUSION: Administration of the prostaglandin E-2 insert led to a sustained increase in circulating PGEM levels in women who had labor induction. Peak PGEM levels correlated with Bishop, score improvement. Rapid increases in prostaglandin E-2 levels might cause tachysystole. (J Soc Gynecol Investig 2000;7:338-42) Copyright (C) 2000 by the Society for Gynecologic Investigation.