Plasma prostaglandin E(2) metabolite levels during labor induction with a sustained-release prostaglandin E(2) 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 end 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.