Oral sustained-release ritodrine as a substitute for prolonged intravenous tocolysis.

Prolonged administration of intravenous ritodrine is necessary in some pregnant women with recurrent preterm labor as serum levels achieved by oral administration of ritodrine are insufficient to prevent recurrent contractions. New oral sustained-release ritodrine at 320 mg/day was given to 38 women with recurrent preterm labor. Serum levels of the drug at this dosage are considered comparable with levels achieved by i.v. treatment. The average duration of treatment was 8 days (range, 1-22). Patient tolerance was acceptable, and major maternal complications did not occur. We conclude that in selected cases, it may be possible to substitute oral sustained-release ritodrine at 320 mg/day for prolonged i.v. treatment.