Antiepileptic drug clearances during pregnancy and clinical implications for women with epilepsy

Objective To characterize the magnitude and time course of pregnancy-related clearance changes for different antiepileptic drugs (AEDs): levetiracetam, oxcarbazepine, topiramate, phenytoin, and valproate. A secondary aim was to determine if a decreased AED serum concentration was associated with increased seizure frequency.

Methods Women with epilepsy were enrolled preconception or early in pregnancy and prospectively followed throughout pregnancy and the first postpartum year with daily diaries of AED doses, adherence, and seizures. Study visits with AED concentration measurements occurred every 1–3 months. AED clearances in each trimester were compared to nonpregnant baseline using a mixed linear regression model, with adjustments for age, race, and hours postdose. In women on monotherapy, 2-sample t test was used to compare the ratio to target concentrations (RTC) between women with seizure worsening each trimester and those without.

Results AED clearances were calculated for levetiracetam (n = 18 pregnancies), oxcarbazepine (n = 4), topiramate (n = 10), valproate (n = 5), and phenytoin (n = 7). Mean maximal clearances were reached for (1) levetiracetam in first trimester (1.71-fold baseline clearance) (p = 0.0001), (2) oxcarbazepine in second trimester (1.63-fold) (p = 0.0001), and (3) topiramate in second trimester (1.39-fold) (p = 0.025). In 15 women on AED monotherapy, increased seizure frequency in the first, second, and all trimesters was associated with a lower RTC (p < 0.05).

Conclusion AED clearance significantly changes by the first trimester for levetiracetam and by the second trimester for oxcarbazepine and topiramate. Lower RTC was associated with seizure worsening. Early therapeutic drug monitoring and dose adjustment may be helpful to avoid increased seizure frequency.