A recent report from your journal has suggested that transdermal nitroglycerin may be an effective tocolytic with fewer side effects than beta agonists1. This is supported by other recent reports2. The rationale for this treatment is based on the finding that nitroglycerin, a nitrous oxide donor, increases levels of cGMP in uterine smooth muscle cells and ultimately cause uterine relaxation. However you have also reported that nitrous oxide donors are effective at inducing cervical ripening in the first trimester3. Studies using a tocolytic which may have cervical ripening properties should therefore include data on intermediate as well as short term premature delivery rates. The study by Smith et al. looked only at delivery rates within 48 hours and did not include data for delivery beyond this time.
We support Smith's suggestion of a large multicentre trial to assess the efficacy and safety of nitroglycerin as a tocolytic; however, we would like to emphasise the need also to further investigate its potential for cervical ripening. Delivery outcome data at 7 and 14 days following treatment would be advisable in any further trials.
A drug that causes uterine relaxation with an increased chance of subsequent labour could be suitable for external cephalic version when delivery is desirable soon after the procedure, to prevent reversion.