Ecase #1-C

Angelina Platas, M.D.

December 26-January 4, 2002

A 30 yo woman has well-controlled epilepsy while taking phenobarbital, but she wants to get pregnant in the next 6 months. Her last generalized seizure was 3 weeks ago after she ran out of her phenobarbital 2 weeks earlier. Now that she is taking phenobarbital again, she is doing well. Other than the seizure 3 weeks ago, she has had no other spells during the past year. While taking phenobarbital, her EEG is normal. The patient is taking a prenatal vitamin with folate. (This is actually a MKSAP question, but I had a similar patient present to clinic, she was already 9 weeks pregnant, on phenobarbital.)

1. What anticonvulsant medications are safe (if any) during pregnancy?

2. Should this patient's medications be continued?

3. What special precautions should be taken during pregnancy if the patient continues phenobarbital?

Most anticonvulsants (including phenobarbital, dilantin, valproate, lithium) are FDA drug classification D (evidence of risk, but are used in cases where benefit outweighs risk to fetus). This is partially because it has been difficult to determine the teratogenic effects of many antiseizure drugs because maternal history of seizure disorder confers an increased risk of congenital anomalies. Of the commonly used anticonvulsants, phenobarbital is actually the one with the best side effect profile and lowest risk of teratogenicity as it pertains to pregnancy.

Forty percent of women will have increased seizure activity during pregnancy. There is also increased risk for poor fetal outcomes in women who experience tonic-clonic seizures during pregnancy. Patients need to be advised of the increased risk for developmental and congenital abnormalities in the fetus as well as increased fetal risk because of maternal seizures.

This patient should certainly be continued on her phenobarbital as it has given her such good seizure control. It is important to discuss any factors that may contribute to seizure control such as good sleep habits and strict medication adherence. Folate should be taken throughout pregnancy.

Phenobarbital is metabolized by the liver, and free phenobarbital levels are affected by the amount of binding proteins made in the liver. Binding proteins are made in an estrogen-dependant process, thus there are higher levels during pregnancy. This patient should have free plasma levels and liver function tests every 1-3 months during pregnancy.

References

Scheuer ML, Pedley TA. The evaluation and treatment of seizures. N Engl J Med. 1990;323:1468-74.Thacker HL. Medical Aspects of pregnancy. J Women's Health. 1999;335-346.