Tocolysis with beta-adrenergic receptor agonists

Beta-adrenergic receptor agonists have been used for tocolysis in the setting of preterm labor for more than three decades. One of these agents, ritodrine hydrochloride, is the only Federal Drug Administration (FDA) approved drug for the treatment of preterm labor. Despite their widespread use, only a few prospective randomized placebo-controlled trials have been performed. These agents have been shown to have more patients deliver beyond 48 hours after the onset of treatment as compared with controls, but have never shown a difference in neonatal outcomes. Because they are one of the few tocolytic agents to have been shown to make a difference when compared with controls, the beta-agonists are commonly used as the control groups in studies examining the efficacy of newer tocolytic agents. In general, agents such as nifedipine, magnesium sulfate, and atosiban have not been shown to be more efficacious than the beta-agonists. However, several studies have shown these agents to have less side effects and lower discontinuation rates than the beta-agonists.