NO donors are superior to placebo or no treatment, but inferior to prostaglandins for first-trimester cervical ripening, and associated with more side effects.
Outpatient cervical ripening before first-trimester surgical abortion: a comparison between misoprostol and isosorbide mononitrate.
Vaginal administration of prostaglandin analogues as well as nitric oxide donors before first-trimester surgical abortion has been shown to induce effective cervical ripening. In addition, nitric oxide donors, such as isosorbide mononitrate and nitroglycerin, have been associated with a patient-friendly side-effect profile when administered 3 h before the surgical procedure. We wanted to compare the cervical ripening effect and possible side effects of isosorbide mononitrate and the prostaglandin analogue misoprostol when self-administered at bedtime the evening before surgical abortion.
                One hundred and twenty nulliparous women scheduled for suction termination of pregnancy in the first trimester were randomly assigned to receive per vaginam either 40 mg of isosorbide mononitrate or 200 microg of misoprostol. Sixty of the women were included for assessment of cervical ripening as well as evaluation of side effects. The other 60 women were recruited for assessment of side effects only. Cervical ripening was evaluated by measuring baseline cervical dilation and the cumulative force to dilate the cervix to 9 mm by means of a cervical tonometer. For assessment of side effects, the women were asked to complete a symptom questionnaire.
                Cervical resistance was significantly higher in women treated with isosorbide mononitrate compared to misoprostol (median cumulative force 73 versus 15 N). Common side effects of misoprostol were abdominal pain (69%), nausea (44%), and vaginal bleeding (66%), while in the isosorbide mononitrate group headache was frequently experienced (79%). In both treatment groups, the frequency and intensity of side effects gradually increased during the treatment interval.
                Misoprostol induced a more pronounced cervical ripening than isosorbide mononitrate, but both regimens were associated with a high frequency of side effects.