A multicenter evaluation of intramuscular ritodrine hydrochloride as initial parenteral therapy for preterm labor management.

Ninety-four patients in documented preterm labor received three intramuscular injections of ritodrine hydrochloride over an interval of 6 hours. They subsequently received the tocolytic agent intravenously for a minimum of 6 hours. The effects of ritodrine on uterine activity and the cardiovascular system were determined. Intramuscular ritodrine hydrochloride elicited a prompt and sustained reduction in the frequency of uterine contractions. The transition to intravenous treatment was achieved without an increase in uterine activity. Seventy percent of the patients had a sustained interval of uterine quiescence, and 96% had at least a 24-hour delay in delivery. Initial parenteral therapy with intramuscular ritodrine hydrochloride is safe and effective and may provide an alternative to intravenous therapy and a means of managing preterm labor during interhospital transport of a patient.