Antiepileptics- clinical applications
The incidence of birth defects in epileptic women taking anticonvulsants is 2-3 times that of the general population. The highest rate is with multiple drug therapy, then phenytoin, followed by sodium valproate, carbamazepine and phenobarbitone.
There is an increased risk of spina bifida (1-2%) with sodium valproate and carbamazepine, particularly in combination with phenytoin. To reduce the risk, folic acid 0.5-4.0 mg daily is recommended, beginning before conception and continuing until the end of the first trimester. A dysmorphic, Binder-like syndrome (mid-facehypoplasia) may also occur, particularly with phenytoin. It may be associated with developmental problems.
Anticonvulsant levels should be monitored frequently with dose adjustments based on clinical condition, seizure frequency and free anticonvulsant concentration. Total concentration levels may give a false impression and lead to a tendency to increase dosage (see 'Drug protein binding' Aust Prescr 1992;15:56-7). Postpartum anticonvulsant concentrations should be monitored closely to prevent toxicity in either the mother or infant.
To avoid neonatal haemorrhage which is associated with maternal antiepileptic therapy, particularly phenytoin, the mother is given vitamin K by injection from 2-48 hours before delivery, and the infant should receive a vitamin K injection at birth.
Breast-feeding may be undertaken, with close monitoring of the infant for any signs of prolonged drowsiness or feeding problems (most likely with clonazepam or phenobarbitone).