Isosorbide Mononitrate versus Misoprostol for Cervical Ripening

Abstract

Objective: To compare the efficacy and safety of isosorbide mononitrate (IMN) versus misoprostol used to induce labour for overdue pregnancy.
Setting: A prospective randomized clinical study conducted at AL-Elwiya Maternity Teaching Hospital in Baghdad from Jan. 2008 to Dec. 2008.
Method: One hundred and fifty women with over due pregnancy (past date and posterm pregnancy) referred for induction of labour with Bishop scores <_ 5 were randomly allocated to receive either forty mg isosorbide mononitrate (IMN) tablet as a single vaginal dose (n=75) or fifty mcg misoprostol vaginally (n=75) every six hrs for a maximum of three doses. Amniotomy and/or oxytocin infusion is considered when Bishop scores frankly progressed (augmentation) or used when no improvement achieved after 24 hour (induction). Adverse effects of medications, induction - delivery interval, mode of delivery and neonatal outcome were recorded and subjected to statistical analysis.
Results: Isosorbide mononitrate was associated with less adverse effects than misoprostol especially regarding uterine tachysystol (0 with isosorbide mononitrate vs 12% with misoprostol, P<0.01) and hyperstimulation (0 with isosorbide mononitrate vs 16% with misoprostol, p<0.01) but the induction - delivery interval with isosorbide mononitrate group was significantly longer compared with misoprostol (26.3±7.3hrs vs 15.4±5.4 hrs , p<0.01). Oxytocin was added to 70 women (93.3%) used isosorbide mononitrate while to 15 women (20%) used misoprostol (p<0.001). Caesarean rate was not significantly different between the two groups, but the indications were different, dystocia is the major cause (73.3%) with isosorbide mononitrate while persistent non-assuring fetal heart rate pattern (64%) in the misoprostol group.
Conclusion: Cervical ripening and induction of labour using isosorbide mononitrate resulted in fewer adverse effects but it was less effective than misoprostol.