Diltiazem for maintenance tocolysis of preterm labor: comparison to nifedipine in a randomized trial

The objective of this study was to compare the safety and efficacy of maintenance tocolysis with oral diltiazem to oral nifedipine in achieving 37 weeks gestation. After successful intravenous tocolysis with magnesium sulfate, 69 women with preterm labor at <35 weeks gestation were randomly assigned to nifedipine (20 mg orally every 4-6 hr), or diltiazem (30-60 mg orally every 4-6 hr). The primary outcome was the percentage of patients achieving 37 weeks gestation. Maternal cardiovascular alterations and neonatal outcomes were also assessed. Sixty-nine patients were available for final analysis. Less patients on diltiazem as compared to nifedipine achieved 37 weeks (15.1% vs. 41.7%, P = 0.019). Gestational age at delivery was also less for patients receiving diltiazem (35.5 +/- 3.5 weeks vs. 33.4 +/- 3.9 weeks, P = 0.022). There were fewer days gained in utero from randomization to delivery with diltiazem as compared to nifedipine; however, this difference was not statistically significant (22.4 +/- 16.3 days vs. 31.2 +/- 24.4 days, P = 0.084). Maternal blood pressure and pulse during tocolysis did not differ significantly between groups. Despite the theoretical advantages of diltiazem tocolysis, maintenance tocolysis with diltiazem offered no benefit over nifedipine in achieving 37 weeks gestation. The cardiovascular alterations with either drug in normotensive, pregnant patients appear minimal.