Medication safety during pregnancy

October 1, 2010

Nearly half of women 18 to 44 years old use prescription drugs. Therefore clinicians must be prepared to counsel these patients regarding medication use during conception and pregnancy.

Key Points

Nearly half of women 18 to 44 years old use prescription drugs.1 Therefore, clinicians must be prepared to counsel these patients regarding medication use during conception and pregnancy.

A recent American Academy of Neurology guideline on the management of epilepsy during pregnancy recommends avoiding polypharmacy as well as monotherapy with valproate.4 Use of multiple antiepileptic drugs (AEDs) during pregnancy is associated with an increased risk of major congenital anomalies.5 Valproate, an older AED, has been linked to an increased risk of neural tube defects and facial clefts.5,6 Teratogenicity data are becoming available for lamotrigine and levetiracetam, 2 commonly used newer AEDs.

Final data from the International Lamotrigine Pregnancy Registry covered 2,444 women and 2,492 pregnancy outcomes between September 1992 and June 3, 2009.7 The rate of major defects associated with first-trimester exposure to lamotrigine was 2.2% for monotherapy and 2.8% for polytherapy with AEDs other than valproate.7 (By comparison, the incidence of birth defects in the general population is about 3%.8 ) The highest rate of major birth defects (10.7%) was seen after first-trimester exposure to lamotrigine in polytherapy regimens that included valproate.7

Limitations of this registry should be noted. It was powered to detect only a large increase in specific birth defects. As with most registries, an internal control group of nonexposed patients was not available. Voluntary enrollment introduces the possibility of selection bias. Ascertainment bias also exists because data were collected from 43 countries with different methodologies.

Data from the North American AED registry suggested a possible link between first-trimester lamotrigine exposure and orofacial clefts.9 However, no such association was found in a large case-control study, and there were only 2 cases of cleft palate among 629 infants with first-trimester exposure to lamotrigine in the International Lamotrigine Pregnancy Registry.7,10

A registry from the United Kingdom provided prospective data on 117 first-trimester exposures to levetiracetam, including 39 cases of monotherapy and 78 cases of polytherapy.11 Major congenital malformations were noted in 3 (2.7%) patients, all of whom were also exposed to other AEDs.11 A recent review of 147 cases of levetiracetam exposure during pregnancy found no significant increase in risk of major congenital malformations.12 Levetiracetam levels should be monitored during pregnancy because of enhanced clearance, particularly in the third trimester.13

When use of AEDs is necessary to maintain seizure control during pregnancy, monotherapy with an AED other than valproate is preferred. The optimal time to make changes to AED regimens is before pregnancy; much of the risk accrues early in the first trimester, and it is best to ensure that seizures are controlled without complications on a new regimen before conception.4