Isoproterenol Pregnancy and Breastfeeding Warnings
Isoproterenol Pregnancy Warnings
Isoproterenol crosses the human placenta. In vitro studies show that 2.8% to 27.3% of a labeled isoproterenol dose crosses the placental barrier within 10 minutes; of the amount that crosses, 92% to 96% was isoproterenol, the rest being metabolite. The Collaborative Perinatal Project reported 31 of 50,282 mother-child pairs reviewed were exposed to isoproterenol. Of the 31 pairs, two malformed children were born; the malformations were not described. The crude relative risk for malformations associated with isoproterenol was calculated to be 1.00, the hospital standardized relative risk, 0.94, and the survival and race standardized risk 1.02. In general, there was a trend for increased risk of minor, non-life-threatening malformations with some sympathomimetic agents, especially eye and ear malformations, but information specific to isoproterenol is unavailable. Isoproterenol is known to inhibit human uterine contractile intensity, but not necessarily contractile frequency, at concentrations less than 10 mcM/L. At concentrations greater than 10 mcM/L, limited in vitro data show that isoproterenol enhances uterine contraction force. Limited data from 5 pregnant women at term show that the dosage required to produce a 25% increase in mean maternal heart rate averages 3.6 mcg, which is significantly more than that required in nonpregnant women (0.7 mcg) or pregnant women at term with mild preeclampsia (0.8 mcg). The significant difference between preeclamptic and non-preeclamptic pregnant women complicates efforts to design a chronotropic epidural anesthesia test dose that is both safe and effective for all pregnant women. In these dose-finding studies, no fetal distress was associated with isoproterenol; one case of fetal heart rate deceleration two minutes after the mother received 0.25 mcg was associated with a Braxton-Hicks contraction.
Isoproterenol has been assigned to pregnancy category C by the FDA. Animal studies have shown evidence of teratogenicity, but teratogenicity has not been reported in humans. There are no controlled data in human pregnancy. Isoproterenol is only recommended for use during pregnancy when there are no alternatives and benefit outweighs risk.
Isoproterenol Breastfeeding Warnings
There are no data on the excretion of isoproterenol into human milk. The manufacturer recommends that caution be used when administering isoproterenol to nursing women.
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