Phenytoin-induced cleft palate:: Evidence for embryonic cardiac bradyarrhythmia due to inhibition of delayed rectifier K+ channels resulting in hypoxia-reoxygenation damage

Background: Phenytoin (PHT) teratogenicity has been related to embryonic arrhythmia due to the capacity of PHT to block I, channels pharmacologically, resulting in hypoxia-reoxygenation damage. The aim of this study was to further elucidate the proposed mechanism. Methods: Pregnant CD-1 mice were given PHT (85 mg/kg) or saline intraperitoneally on gestational days 10-11. Embryonic heart rhythm and presence of hemorrhage in orofacial region was recorded on day 12, fetuses were examined for malformations on day 18. Embryonic heart rate was also recorded on individual days after dosing days 9-16. In addition, PHT was given at doses of 10, 25, or 85 mg/kg on day 12 for analysis of plasma concentrations. Results: PTH-induced bradycardia and arrhythmia in similar to 20% of the embryos, 48% showed hemorrhage in the orofacial region; 39% of the fetuses had cleft palate. The region in which hemorrhages were visible in the embryo corresponded with the region where tissue deficiency (cleft palate) was visible in the fetus at term. None of the controls showed hemorrhages, dysrhythmia, or cleft palate. PHT affected embryonic heart rates on days 9-13, but not on days 14-16. Single dose administration an day 12, the most sensitive day, resulted in a dose-dependent decrease in embryonic heart rate (12-34%). Embryonic arrhythmia occurred at 25 and 85, but not at 10 mg/kg or in the controls. Mean maternal free plasma concentrations were 6 and 14 mu mol/L in the 10- and 25-mg/kg groups, respectively. Conclusions: PHT-induced cleft palate was preceded by embryonic dysrhythmia and hemorrhage in the orofacial region. Embryonic heart rhythm was phase specifically affected, as described for selective I-Kr channel blockers, at clinically relevant concentrations. The results support the idea that PHT teratogenicity is a consequence of pharmacologically induced dysrhythmia and hypoxia-related damage.