MATERNAL AND FETAL PLASMA-CONCENTRATIONS OF RITODRINE

  • 1 January 1985
    • journal article
    • research article
    • Vol. 65  (6) , 793-797
Abstract
Previous studies using other .beta.-adrenergic drugs for tocolysis suggest that if treatment fails and the patient delivers shortly after the therapy is discontinued, there is a direct correlation between neonatal drug concentration and major neonatal complications. The disposition of ritodrine was studied in 28 maternal-infant pairs in whom i.v. ritodrine was administered for clinical indications. The fetal to maternal ratio of ritodrine was 1.17 .+-. 0.48. The concentration or ritodrine in both maternal and umbilical vein was found to vary inversely with the length of time the drug was discontinued before delivery. A stepwise multilinear regression revealed that the maternal ritodrine dose in the 24 h before delivery and the drug discontinuance to delivery interval were both independently related to umbilical vein ritodrine concentrations. When combined, the 2 variables explained 52% of the variance in umbilical vein ritodrine levels. The frequency of respiratory distress syndrome was increased in the neonates in whom umbilical vein ritodrine was greater than 10 ng/ml, compared with the groups with umbilical vein levels ranging from 3.0-10.0 ng/ml. Neonates with the highest ritodrine concentration were also of lower gestational age (29.4 vs. 33.5 wk, P < .05) and had greater inherent risk of prematurity-related complications.