Lamotrigine clearance rises steeply in pregnancy, driven by oestrogen, and levels can fall by half or more, most sharply in the first and second trimesters. Seizure control can slip without any change in the patient's adherence.
Measure a baseline trough level before or early in pregnancy, when seizures are controlled. Repeat it every trimester, or monthly where available, and adjust the dose to keep near baseline. After delivery clearance falls back within weeks, so plan a step-down to avoid toxicity.
- Take a baseline trough level before conception or in early pregnancy
- Repeat each trimester and after any seizure
- Increase the dose to restore the baseline level
- Plan a postpartum dose reduction over the first 2 to 3 weeks
Why it matters
The safest monotherapy for fetal growth only protects the mother if its level is maintained.
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