Clinical safety rating: safe
Human studies have proved safety
Stabilizes neuronal membranes by blocking voltage-gated sodium channels and inhibiting the release of excitatory neurotransmitters, particularly glutamate and aspartate.
| Metabolism | Primarily metabolized by UDP-glucuronosyltransferases (UGT1A4, UGT2B7). Minimal involvement of CYP450 enzymes. Autoinduction of its own metabolism with chronic use. |
| Excretion | Renal (94% as metabolites, 10% unchanged; 2% fecal) |
| Half-life | 25.4 h (range 24-31 h, prolonged to 59 h with valproate) |
| Protein binding | 55% (binds to albumin) |
| Volume of Distribution | 1.2 L/kg (distribution into tissues, including brain) |
| Bioavailability | Oral: 98% (immediate-release); ~90% (extended-release) |
| Onset of Action | Oral: 1-2 weeks for initial effect; up to 6 weeks for full therapeutic response |
| Duration of Action | ~24 h (once-daily dosing for extended-release; twice-daily for immediate-release) |
| Molecular Weight | 256.09 |
Initial: 25 mg orally once daily for 2 weeks, then 50 mg once daily for 2 weeks, then increase by 50 mg every 1-2 weeks. Maintenance: 100-200 mg twice daily (200-400 mg/day). Maximum: 400 mg/day.
| Renal impairment | eGFR <30 mL/min/1.73 m²: use with caution; no specific dose adjustment recommended. eGFR <10 mL/min: reduce dose by 50% and monitor. |
| Liver impairment | Child-Pugh Class B: reduce dose by 50%. Child-Pugh Class C: reduce dose by 75%. |
| Pediatric use | 2-12 years: 0.15 mg/kg/day once daily for 2 weeks, then 0.3 mg/kg/day once daily for 2 weeks, then increase by 0.3 mg/kg/day every 1-2 weeks. Maintenance: 1-5 mg/kg/day divided twice daily. Maximum: 400 mg/day. |
| Geriatric use | Lower initial doses (25 mg every other day) and slower titration due to increased sensitivity and slower clearance; monitor for adverse effects. |
| 1st trimester | Teratogenic; associated with increased risk of cleft palate and other congenital anomalies. Use only if benefit outweighs risk. |
| 2nd trimester | Risk of neural tube defects and other malformations persists. Avoid unless essential. |
| 3rd trimester | May cause neonatal withdrawal, coagulopathy, and hepatotoxicity. Use with caution, monitor neonate. |
Clinical note
The preferred antiepileptic drug for women of reproductive age and the most commonly used AED in pregnancy. Associated with the lowest major congenital malformation (MCM) rate of the major AEDs in the largest pregnancy registries (NAAED: approximately 2.0–2.4% vs. 2–3% background rate for low doses). Dose-dependent teratogenicity seen only at high doses (>300 mg/day) in some registries, but risk at therapeutic doses is low. Critical caveat: pregnancy significantly increases lamotrigine clearance (by up to 2–3×), requiring dose adjustment to prevent breakthrough seizures.
| Placental transfer | Complete; lamotrigine crosses the placenta readily, with cord blood levels approximately 50-100% of maternal serum levels. |
■ FDA Black Box Warning
Life-threatening rashes, including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), especially in pediatric patients and with rapid dose escalation.
| Serious Effects |
Hypersensitivity to lamotrigine or any component
| Precautions | Risk of serious rash (SJS/TEN); hemophagocytic lymphohistiocytosis (HLH); aseptic meningitis; multiorgan hypersensitivity reactions; suicidal thoughts and behavior; blood dyscrasias; cardiac conduction abnormalities; increased seizure frequency with abrupt withdrawal. |
| Food/Dietary | No significant food interactions. Grapefruit has no effect. Alcohol may increase CNS depression and dizziness; limit or avoid. |
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| Breastfeeding |
| Lamotrigine is excreted into breast milk in moderate amounts; infant serum levels can reach therapeutic ranges. Monitor infant for rash, drowsiness, and poor feeding. Benefit of breastfeeding may outweigh risks in many cases, but caution advised. |
| Lactation Rating | L3 (Moderately Safe) or 'Potential Hazard' per some sources. |
| Teratogenic Risk | First trimester exposure increases risk of oral clefts (cleft lip/palate) (absolute risk ~0.3-0.9% vs 0.2% background). Second/third trimester: risk of neural tube defects, cardiac malformations, and developmental delay. Higher doses (>300 mg/day) and polytherapy increase risk. Folate supplementation recommended. |
| Fetal Monitoring | Monitor serum lamotrigine levels every 4-6 weeks during pregnancy and postpartum. Assess for seizure control and adverse effects. Fetal ultrasound for structural anomalies (cleft lip/palate, neural tube defects). Neonatal monitoring for withdrawal, rash, or apnea. |
| Fertility Effects | No significant negative impact on fertility. Limited data; possible decrease in libido or menstrual irregularities in some women. No impairment of oocyte quality or sperm parameters reported. |
| Clinical Pearls |
| Titrate slowly to minimize risk of Stevens-Johnson syndrome; start 25 mg/day for weeks 1–2, then 50 mg/day for weeks 3–4. Drug interactions: valproate doubles lamotrigine half-life and increases SJS risk; estrogen-containing contraceptives reduce lamotrigine levels by ~50%. Therapeutic serum level: 2.5–15 mcg/mL. Monitor for rash, especially in first 8 weeks. |
| Patient Advice | Report any rash, hives, or blisters immediately; may be sign of serious skin reaction. · Do not stop taking abruptly; taper under doctor's guidance to avoid rebound seizures. · Take missed dose as soon as remembered unless close to next dose; do not double. · Oral contraceptives and hormone therapy can reduce lamotrigine effectiveness; discuss with doctor. · Avoid driving or operating machinery until effects are known; may cause dizziness or blurred vision. |