monitoring antiepileptics in pregnancy

Last edited 01/2021 and last reviewed 01/2021

Monitoring and dosing advice in pregnancy

For any antiepileptic drug that is used during pregnancy, it is recommended to use monotherapy treatment and the lowest effective dose, where possible. Physiological changes during pregnancy (and post-partum) can affect concentrations of antiepileptic medicines, particularly for lamotrigine and phenytoin.

Key issues are described below. However, prescribers should consult advice from the SmPC and relevant clinical guidance for dosing and monitoring recommendations of any antiepileptic drugs in pregnancy.

Lamotrigine

• have been reports of decreased lamotrigine plasma levels during pregnancy with a potential risk of loss of seizure control. After birth, lamotrigine levels may increase rapidly with a risk of dose-related adverse events
• therefore, lamotrigine serum concentrations in the woman should be monitored before, during, and after pregnancy, including shortly after birth. If necessary, the dose should be adapted to maintain the lamotrigine serum concentration at the same level as before pregnancy or adapted according to clinical response. In addition, dose-related undesirable effects should be monitored after birth

Levetiracetam

• decrease in levetiracetam plasma concentrations has been observed during pregnancy
• decrease is more pronounced during the third trimester (by up to 60% of baseline concentration before pregnancy). Appropriate clinical management of pregnant women treated with levetiracetam should be ensured

Oxcarbazepine

• data from a limited number of women indicate that plasma levels of the active metabolite of oxcarbazepine, the 10-monohydroxy derivative (MHD), may gradually decrease throughout pregnancy
• is recommended that clinical response should be monitored carefully in women receiving oxcarbazepine during pregnancy to ensure that adequate seizure control is maintained. Measurement of MHD plasma concentrations should be considered. If dosages have been increased during pregnancy, postpartum MHD plasma levels may also be considered for monitoring.

Phenytoin

• an increase in seizure frequency may occur during pregnancy because of altered phenytoin pharmacokinetics. Periodic measurement of plasma phenytoin concentrations may be valuable in the management of pregnant women as a guide to appropriate adjustment of dosage

Reference:

• MHRA(January 2021).Antiepileptic drugs in pregnancy: updated advice following comprehensive safety review Drug Safety Update volume 14, issue 6: January 2021: 1