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Antiepileptic Drug (AED) Pregnancy: Discuss risk vs benefit; register with UK Epilepsy and Pregnancy Register; dose often needs increase in pregnancy

Lamotrigine

Brand names: Lamictal

Adult dose

Dose: 25-50 mg/day initially, increasing to 100-200 mg/day (monotherapy)
Route: Oral
Frequency: Once or twice daily
Max: 500 mg/day (adjunct with enzyme inducers)
Dose titration is slow — rash risk with rapid escalation. With valproate: start at 25 mg every other day

Paediatric dose

Dose: 0.15-0.3 mg/kg/day initially (with valproate); 0.6 mg/kg/day (with enzyme inducers) mg/day/kg
Route: Oral
Frequency: Once or twice daily
Max: 15 mg/kg/day or 400 mg/day (whichever is less)
Child 2-12 years (adjunct without valproate, without enzyme inducers): Weeks 1-2: 0.3 mg/kg/day; Weeks 3-4: 0.6 mg/kg/day; then increase by max 0.6 mg/kg every 1-2 weeks. With valproate (halves lamotrigine clearance): start at half these doses. With enzyme inducers (carbamazepine, phenytoin): use higher doses. Licensed 2 years and over

Dose adjustments

Renal

Use with caution — active metabolite may accumulate

Hepatic

Reduce by 50% (moderate hepatic impairment); reduce by 75% (severe)

Paediatric weight-based calculator

Child 2-12 years (adjunct without valproate, without enzyme inducers): Weeks 1-2: 0.3 mg/kg/day; Weeks 3-4: 0.6 mg/kg/day; then increase by max 0.6 mg/kg every 1-2 weeks. With valproate (halves lamotrigine clearance): start at half these doses. With enzyme inducers (carbamazepine, phenytoin): use higher doses. Licensed 2 years and over

Clinical pearls

  • Rash occurs in approximately 10% of patients — do not re-challenge; risk of Stevens-Johnson Syndrome or toxic epidermal necrolysis, especially with rapid escalation or concomitant valproate
  • MHRA 2019: Lamotrigine associated with serious skin reactions — slow titration is essential
  • Valproate doubles lamotrigine plasma levels — always adjust starting dose downward when co-prescribing
  • Suitable alternative to valproate in girls of childbearing potential — avoid valproate in women of childbearing potential per MHRA/NICE guidance
  • Effective for generalised and focal epilepsy; also used in Lennox-Gastaut syndrome

Contraindications

  • Hypersensitivity to lamotrigine

Side effects

  • Skin rash (early — risk of SJS/TEN)
  • Dizziness
  • Headache
  • Diplopia
  • Ataxia
  • Insomnia
  • Nausea

Interactions

  • Sodium valproate (significantly increases lamotrigine levels — halve initial dose)
  • Carbamazepine / phenytoin (reduce lamotrigine levels)
  • Combined oral contraceptives (reduce lamotrigine levels by 50% — seizure risk)
  • Sertraline (increases lamotrigine levels)

Monitoring

  • Skin surveillance especially weeks 2-8
  • Liver function tests if hepatic symptoms develop
  • FBC if haematological symptoms

Reference: BNF for Children; NICE NG217 (Epilepsy); MHRA Drug Safety Update (lamotrigine rash); BNF 90. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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