PT  - JOURNAL ARTICLE
AU  - M R Wright
AU  - D W Rurak
AU  - M P van der Weyde
AU  - S M Taylor
AU  - J E Axelson
TI  - Clearance and disposition of ritodrine in the fluid compartments of the fetal lamb during and after constant rate fetal intravenous infusion.
DP  - 1991 Sep 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 897--902
VI  - 258
IP  - 3
4099  - http://jpet.aspetjournals.org/content/258/3/897.short
4100  - http://jpet.aspetjournals.org/content/258/3/897.full
SO  - J Pharmacol Exp Ther1991 Sep 01; 258
AB  - The disposition of the beta-2 adrenoreceptor agonist, ritodrine, has been examined in the fetal lamb during and after constant rate fetal intravenous infusion (8-24 h). Samples were collected from the fetal femoral artery, umbilical vein, maternal femoral artery, uterine vein, fetal trachea and the amniotic activity for ritodrine quantitation. The amniotic fluid was also analyzed for conjugated metabolites of ritodrine. Ritodrine appears to be cleared across the sheep placenta only to a limited extent (placental clearance 9.2 +/- 2 ml/min/kg; mean +/- S.E.M.). There is, however, significant fetal nonplacental clearance of ritodrine (fetal nonplacental clearance 52.8 +/- 8.0 ml/min/kg). At least part of this clearance appears to be due to fetal drug metabolism, as evidenced by the accumulation of glucuronide conjugates of ritodrine in the amniotic fluid. Ritodrine was also shown to accumulate in the amniotic and fetal tracheal fluids and persist after fetal arterial plasma ritodrine concentrations became undetectable. The accumulation of ritodrine in the tracheal fluid may be of pharmacologic significance, given the well documented, potent effects of beta-2 agonists on fetal lung function and development.