Abstract
In an accompanying abstract, we offer evidence that maternally administered digoxin does not readily cross the placenta of fetuses with cardiac disease. We have now administered digoxin and digitoxin to a fetus i.m. with supraventricular tachycardia in the late second trimester after maternally administered digoxin, verapamil, and procainamide failed. Fetal blood specimens were obtained by percutaneous umbilical blood sampling. Despite a sustained maternal digoxin concentration > 1.8 ng/ml, the maximum fetal digoxin (FD) was 0.86 ng/ml. 25 mcg of digoxin was placed into the fetal thigh q 8h x 3. The FD level 8h post load was below baseline. A reload of 50 mcg IM q 6h x 4 doses resulted in a FD of 1.51 ng/ml and a normal sinus rate. A second sample obtained 7.3h later was 1.1 ng/ml. The kel was calculated to be 0.0434h x 10-1 and the t½ B was 15.9h. The Vd, estimated assuming a time 0 concentration of 1.9 ng/ml, was 487 ml/kg. Based on the Vd and clearance, a maintainance dose of 80 mcg q 12h was calculated to give a peak of 2.2 ng/ml and a trough of 1.4 ng/ml (actual measured trough was 1.2 ng/ml). In hopes of prolonging the dosing interval, we changed to digitoxin (DT). A 40 mcg load resulted in DT of 5.3 ng/ml and 2.9 ng/ml at 4.25h and 9.25h postdose. The calculated t½ B was 5.8h. Serial measurement of fetal serum and amniotic fluid digoxin/digitoxin suggest some recirculation occurred. This is the first study of human fetal digoxin and digitoxin clearance in a continuing pregnancy after direct fetal administration. Our findings indicate that clearance is strikingly more rapid than in the newborn.
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Welner, C., Thompson, M. DIGOXIN AND DIGITOXIN CLEARANCE IN THE HUMAN FETUS. Pediatr Res 21 (Suppl 4), 243 (1987). https://doi.org/10.1203/00006450-198704010-00455
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DOI: https://doi.org/10.1203/00006450-198704010-00455