What are the concerns and recommendations for a 26-week pregnant woman with a history of seizure or bipolar disorder, experiencing dizziness while taking Lamictal (lamotrigine)?

Dizziness on Lamictal at 26 Weeks Pregnancy

Dizziness is a known side effect of lamotrigine and is generally not harmful, but you must ensure lamotrigine levels are therapeutic through monitoring, as pregnancy significantly increases lamotrigine clearance and may require dose escalation to maintain seizure control or mood stability—the dizziness itself does not necessitate stopping the medication unless it causes functional impairment or falls risk.

Understanding Lamotrigine Safety in Pregnancy

Lamotrigine is considered one of the safest antiepileptic drugs for use during pregnancy based on extensive registry data:

• Lamotrigine demonstrates low teratogenicity and is consistently among the safest medications for fetal development, with reassuring data on both major malformations and cognitive outcomes 1, 2.
• Pregnancy registries across multiple countries have shown no consistent increase in major congenital anomalies with lamotrigine monotherapy 3, 2.
• One registry suggested a possible increased risk of oral clefts, but a large prospective study of 218 lamotrigine-exposed pregnancies found zero cases of oral cleft, making this risk uncertain at best 2.

The Dizziness Issue: Context and Management

Dizziness is a recognized adverse effect of lamotrigine but must be understood in the pregnancy context:

• Dizziness is listed as a common side effect of multiple antiepileptic drugs including lamotrigine 4.
• At 26 weeks gestation, you are in the second trimester where lamotrigine clearance is significantly increased, leading to lower plasma concentrations 5, 6.
• The mean steady-state trough concentration of lamotrigine drops to approximately 2.14 mg/L in the second trimester compared to 4.31 mg/L in non-pregnant women—a 50% reduction 5.

Critical Distinction

The dizziness could represent:

1. Paradoxically low lamotrigine levels (subtherapeutic) rather than toxicity, given pregnancy-induced clearance
2. Physiologic pregnancy changes (orthostatic hypotension, anemia, dehydration)
3. True medication side effect if levels are adequate or elevated

Recommended Management Algorithm

Step 1: Measure Lamotrigine Plasma Concentration Immediately

• Check lamotrigine level now to determine if concentration is below, at, or above the preconception reference concentration 6.
• If no preconception reference exists, establish current level as baseline and monitor trend 6.

Step 2: Assess Dizziness Severity and Fall Risk

• Determine if dizziness causes functional impairment or increases fall risk that could harm mother or fetus.
• Evaluate for orthostatic vital signs, anemia (CBC), and hydration status to rule out pregnancy-related causes.

Step 3: Dose Adjustment Based on Levels

If lamotrigine level is below therapeutic range or preconception reference:

• Increase dose by 20-25% to restore therapeutic concentration 6.
• The dizziness may actually improve with dose optimization if it relates to subtherapeutic control of underlying condition 5, 6.
• Simulations suggest doses of 175 mg twice daily in the second trimester may be needed to maintain target concentrations 5.

If lamotrigine level is therapeutic or elevated:

• Consider timing the dose at bedtime to minimize daytime dizziness impact 4.
• Ensure adequate hydration and rule out other pregnancy-related causes.
• If dizziness is intolerable and confirmed medication-related, consider small dose reduction (10-15%) while maintaining therapeutic monitoring 6.

Step 4: Ongoing Monitoring Protocol

• Measure lamotrigine levels every 4 weeks throughout remainder of pregnancy 6.
• When concentration falls below reference, increase dose by 20-25% and repeat measurement 6.
• Continue this systematic approach through third trimester, where concentrations drop even further (mean 1.51 mg/L) 5.

Critical Safety Considerations

Do Not Discontinue Lamotrigine

• Stopping lamotrigine poses greater risk than continuing it—untreated seizures or mood instability during pregnancy carry significant maternal and fetal risks 1, 2.
• Pregnancy registries demonstrate that benefits of treatment outweigh minimal documented risks when medication is required for daily functioning 1, 2.

Drug Interactions to Consider

• Combined oral contraceptives decrease lamotrigine levels significantly, but this is not relevant at 26 weeks pregnancy 4.
• Ensure no concurrent enzyme-inducing medications that could further reduce lamotrigine levels 4.

Postpartum Planning

• After delivery, lamotrigine clearance rapidly returns to baseline within 1-2 weeks 6.
• Reduce dose by 20-25% in first postpartum week and check level to prevent toxicity 6.
• Repeat reductions until preconception reference concentration is re-established 6.

Common Pitfalls to Avoid

• Do not assume dizziness means toxicity in pregnancy—it may paradoxically indicate subtherapeutic levels due to increased clearance 5, 6.
• Do not rely on clinical assessment alone—therapeutic drug monitoring is essential as pregnancy effects on lamotrigine are unpredictable and vary considerably among patients 6.
• Do not delay dose adjustments—waiting until seizure breakthrough or mood destabilization occurs puts both mother and fetus at risk 5, 6.