Biopharmaceutical aspects of ritodrine retard in pregnant women.

Biopharmaceutical aspects of the new sustained-release formulation of ritodrine, a tocolytic agent, were studied in 9 patients with preterm labour. A mean bioavailability of 26% (range 22%-32%) was estimated after the 4th day of treatment (steady state). A.U.C.'s from oral administration were found to correlate well with those measured in i.v. therapy in the same patients (r = 0.92; p = 0.0004). It was concluded that differences in bioavailability of ritodrine-retard are small enough to enable clinicians, using this sustained release preparation, to make fair estimations of the oral dosage, needed to replace the initial i.v. treatment.