Multiple congenital anomalies associated with in utero exposure of phenytoin: Possible hypoxic ischemic mechanism?

Different fetal effects on fingers from exposure to phenytoin, phenobarbital, and carbamazepine

Exposure at conception to phenytoin (PHT), phenobarbital (PB), and carbamazepine (CBZ) has been associated with several different effects on the fetus, including hypoplasia of the distal phalanges, dysmorphic facial features, and structural abnormalities such as oral clefts and neural tube defects. One question is whether each of these antiepileptic drugs (AEDs) has the same effects or just similar effects. A systematic examination of the fingers of children exposed at conception to PHT, PB, or CBZ, as monotherapy, has been used to address this question. The findings in the examinations of the fingers of 115 AED-exposed children (40, PHT; 34, PB; 41, CBZ) and their parents were compared to the findings in 111 age- and sex-matched children and their parents. The evaluations used were both subjective assessments and objective measurements. Shortening and narrowing of the fifth fingernail and an increased frequency of arch patterns in the dermal ridges were more common in PHT-exposed children. A significant decrease in the length of the nail, but not width, occurred in the PB-exposed children. Stiffness of the interphalangeal joints was more common in the CBZ-exposed children. The findings in children exposed to PHT, PB, or CBZ, as monotherapy, showed that all three exposures in early pregnancy affected the fingers, but the effects were not the same. The most striking effects were present in PHT-exposed children.

Neuroteratogens in man: An overview with special emphasis on the teratogenicity of antiepileptic drugs in pregnancy

The most active growth and development of the human cerebrum and cerebellum occurs in the second half of pregnancy and in the first year of life. It is therefore not surprising that many teratogens may also affect development causing slight, moderate or even severe brain damage. The "classical" antiepileptic drugs (AEDs) valproic acid (VPA), phenytoin, phenobarbital, primidone and carbamazepine are all considered to be teratogenic. They may increase the rate of major congenital anomalies including neural tube defects (NTD), cause specific facial and other dysmorphic features--the "Anti Epileptic Drug Syndrome" (AEDS) and often some degree of mental impairment. Of these AEDs, the most teratogenic seems to be valproic acid, causing about 2% of NTD and an additional increase of 4-8% in major congenital anomalies. Phenytoin also increases the rate of various anomalies, but apparently not of NTD. Phenobarbital primidone and carbamazepine are also teratogenic and impair intellectual function but to a lesser extent than VPA and phenytoin. Cognition is mainly impaired in the children that also exhibit the AEDS. The impairment is slight to moderate, leaving the affected children with a close to borderline intelligence. Lamotrigine monotherapy in pregnancy seems to be relatively safe. In general, polytherapy is more dangerous to the fetus than monotherapy and, at least for VPA and lamotrigine, there seems to be a "threshold effect".

Phenytoin teratogenicity: Hypoxia marker and effects on embryonic heart rhythm suggest an hERG-related mechanism

BACKGROUND

The antiepileptic drug phenytoin (PHT) is a human and animal teratogen. The teratogenicity has been linked to PHT-induced embryonic cardiac arrhythmia and hypoxic damage during a period when regulation of embryonic heart rhythm is highly dependent on a specific K(+) ion current (I(Kr)). PHT has been shown to inhibit I(Kr). The aims of this study were to investigate whether teratogenic doses cause embryonic hypoxia during and after the I(Kr) susceptible period and to further characterize PHT effects on embryonic heart rhythm.

METHODS

Pregnant C57BL mice were administered the hypoxia marker pimonidazole followed by PHT or saline (controls) on GD 10 or GD 15. The embryos were fixed and sectioned, and the immunostained sections were analyzed with a computer assisted image analysis. Effects of PHT (0-250 microM) on heart rhythm in GD 10 embryos cultured in vitro were videotaped and then analyzed by using a digitalization technique.

RESULTS

PHT dose-dependently increased the hypoxia staining (6- and 11-fold after maternal dosing of 100 and 150 mg/kg, respectively) during the period I(Kr) is expressed and functional (GD 10). In contrast, there were no differences between the PHT doses in hypoxia staining, and much less pronounced hypoxia after this period (GD 15). With increasing PHT concentrations, increased length of the interval (bradycardia) and large variations in length between individual heartbeats (arrhythmia) were recorded.

CONCLUSIONS

PHT induced bradycardia/arrhythmia and severe embryonic hypoxia during the I(Kr) susceptible period, supporting the idea of an I(Kr)-arrhythmia-hypoxia-related teratogenic mechanism.