Isosorbide Mononitrate versus Misoprostol for Cervical Ripening

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.