Efficacy and side effect of ritodrine and magnesium sulfate in threatened preterm labor

In terms of efficacy, several previous studies have shown that the success rate in inhibiting preterm labor was not different between magnesium sulfate and ritodrine. However, there is a paucity of information regarding the efficacy of both medications after consideration of intra-amniotic infection, which is one of the most important prognostic factors in patients of threatened preterm birth. The objective of this study was to compare the efficacy and safety of magnesium sulfate with that of ritodrine in preterm labor.

In this retrospective cohort study, we included patients who were admitted and treated with either ritodrine or magnesium sulfate with the diagnosis of preterm labor at 24-33.6 weeks of gestational age between January 2005 to April 2015. Patients were divided into 2 groups according to the first-used tocolytics (ritodrine group and magnesium sulfate group). We compared the efficacy and prevalence of side effect in each group. The efficacy of both tocolytics was evaluated in terms of preterm delivery within 48 hours, 7 days, or 37 weeks of gestation and need for 2nd line therapy.

A total number of 201 patients were enrolled including 177 cases in ritodrine group and 24 cases in magnesium sulfate group. The efficacy of both tocolytics (preterm delivery within 48 hours, 7 days, or 37 weeks of gestation and need for 2nd line therapy) was not different between the 2 groups of cases. In multivariate analysis, gestational age at treatment, twin gestation, intra-amniotic infection and maternal C-reactive protein (CRP) was associated with treatment failure (preterm delivery within 48 hours), but the type of tocolytics was not significantly associated with treatment failure. The type of side effect was different in the 2 groups, but the frequency of total adverse effect, need for discontinuation of therapy because of maternal adverse effect, and severe adverse effect were not different between the two groups of cases.

The efficacy and safety of magnesium sulfate was similar to ritodrine, and can be a substitute tocolytics. Additionally, failure of tocolytic therapy was determined by gestational age at treatment, twin gestation, intra-amniotic infection, and maternal CRP, not by the type of tocolytics.