The concurrent in vitro and in vivo release of PGE2 from a controlled-release hydrogel polymer pessary for cervical ripening

Twenty five patients booked for induction of labour, at 38 weeks or more gestation, were administered a controlled release vaginal polymer pessary containing 10 mg prostaglandin E2 (PGE2), designed to release 0.6 mg per hour in vivo. The release profile from the polymer was linear throughout the eight hour observation period with a correlation coefficient of 0.81, and regression slope of 0.93 mg/hr. with 95% confidence intervals of 0.63 mg/hr. to 1.23 mg/hr. This compared with a concomitant release profile in vitro which was uniform with time for the first five hours, but then continued at a decreasing rate with a correlation coefficient of 0.98. The relationship between PGE2 release and cervical score change was linear, with a correlation coefficient of 0.65. The results show that PGE2 release from the pessary in vivo is predictable, and suggest that the controlled release pessary offers the advantages of greater control of cervical ripening than alternative vehicles currently available.