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Anticonvulsant (Sodium Channel Blocker) Pregnancy: Caution — increased risk of oral cleft (small absolute risk); folic acid supplementation mandatory; levels fall during pregnancy (monitor closely)

Lamotrigine

Brand names: Lamictal

Adult dose

Dose: Monotherapy: starting 25 mg OD × 2 weeks, 50 mg OD × 2 weeks, then increase by 50–100 mg every 1–2 weeks. Target: 100–200 mg/day (OD or BD). With valproate: HALF dose (valproate inhibits lamotrigine clearance).
Route: Oral
Frequency: OD or BD
Max: 500 mg/day (monotherapy); 200 mg/day (with valproate)
Also for bipolar depression (licensed). Titration schedule is critical — rapid titration causes life-threatening SJS/TEN. CRITICAL interaction with valproate: halve the starting dose AND the titration rate.

Paediatric dose

Dose: 0.3 mg/kg
Route: Oral
Frequency: Once daily (titration phase; total 0.3 mg/kg/day initially)
Max: 200 mg/day (with valproate); 400 mg/day (monotherapy)
Concentration: 2 mg, 5 mg, 25 mg, 50 mg, 100 mg, 200 mg dispersible/chewable tablets mg/ml
BNFc child 2–12 years (monotherapy): 0.3 mg/kg OD × 2 weeks, then 0.6 mg/kg OD × 2 weeks, then increase by 0.6 mg/kg/1–2 weeks; target maintenance 1–10 mg/kg/day in 1–2 divided doses. With valproate (CRITICAL — halve dose AND titration rate): 0.15 mg/kg OD × 2 weeks. CYP-inducer co-medication: doubled doses required. Slow titration mandatory — rapid escalation causes life-threatening SJS/TEN.

Dose adjustments

Renal

Caution in severe renal impairment

Hepatic

Reduce dose by 50% (moderate) or 75% (severe) in hepatic impairment

Paediatric weight-based calculator

BNFc child 2–12 years (monotherapy): 0.3 mg/kg OD × 2 weeks, then 0.6 mg/kg OD × 2 weeks, then increase by 0.6 mg/kg/1–2 weeks; target maintenance 1–10 mg/kg/day in 1–2 divided doses. With valproate (CRITICAL — halve dose AND titration rate): 0.15 mg/kg OD × 2 weeks. CYP-inducer co-medication: doubled doses required. Slow titration mandatory — rapid escalation causes life-threatening SJS/TEN.

Clinical pearls

  • Rash risk: slow titration mandatory — rapid increase is the main risk factor for SJS; instruct patients to seek medical attention for any rash
  • Valproate interaction: co-prescription requires careful dose adjustment — HALVE starting dose and double the duration of each titration step
  • OCP interaction: oral contraceptives reduce lamotrigine levels — need to increase dose when on OCP; level drops if OCP stopped (risk of lamotrigine toxicity)
  • Bipolar depression: effective, licensed for prevention of depressive episodes (not acute mania)

Contraindications

  • None absolute beyond hypersensitivity

Side effects

  • Rash (10% — most occur in first 8 weeks; majority benign but some progress to SJS/TEN)
  • Stevens-Johnson Syndrome / TEN (rare, potentially fatal)
  • Headache
  • Dizziness
  • Diplopia
  • Ataxia
  • Lymphadenopathy
  • Aseptic meningitis (rare)

Interactions

  • Valproate — doubles lamotrigine levels (inhibits glucuronidation); HALVE lamotrigine dose and titrate more slowly
  • Carbamazepine — reduces lamotrigine levels by 40%
  • Combined OCP — reduces lamotrigine levels by 50%; adjust dose
  • Rifampicin — reduces lamotrigine levels

Monitoring

  • Plasma lamotrigine levels (especially in pregnancy, drug interactions)
  • Skin rash (first 8 weeks — education essential)
  • Seizure frequency

Reference: BNFc; BNF; BNF for Children; NICE NG217; Lamictal SPC. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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