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Mood Stabiliser (Sodium Channel Blocker) — Bipolar Depression Pregnancy: Use with caution — teratogenic risk lower than valproate/carbamazepine. NICE recommends lamotrigine as preferred mood stabiliser in women of childbearing potential and in pregnancy. Dose requirements increase significantly in pregnancy (oestrogen increases clearance) — monitor levels and increase dose; reduce post-partum.

Lamotrigine (Psychiatric Use)

Brand names: Lamictal

Adult dose

Dose: Bipolar disorder (prevention of depressive episodes — monotherapy): 25mg OD for 2 weeks, then 50mg OD for 2 weeks, then 100mg OD for 1 week, then 200mg OD (target maintenance). With valproate (halve doses — valproate doubles lamotrigine levels): 25mg every other day × 2 weeks, then 25mg OD × 2 weeks, then 50mg OD (target). With enzyme inducers (carbamazepine, phenytoin): double the titration doses.
Route: Oral
Frequency: Once or twice daily
Max: 200mg OD (monotherapy); 400mg OD (with enzyme inducers); 100mg OD (with valproate)
CRITICAL: slow titration is mandatory to minimise risk of Stevens-Johnson syndrome (SJS). Never rush titration. If any rash develops in first 8 weeks — stop immediately and do not rechallenge. NICE CG185: lamotrigine is the preferred maintenance treatment for bipolar depression. Effective for depressive pole of bipolar disorder; minimal efficacy for mania.

Paediatric dose

Dose: 0.3 mg/kg
Route: Oral
Frequency: Once or twice daily
Max: 200mg OD (epilepsy — psychiatric use requires specialist guidance)
BNFc: Licensed for epilepsy from age 2 years. For psychiatric indications: seek specialist child and adolescent psychiatry opinion. Titration schedule varies by concomitant medications — extremely complex in children.

Dose adjustments

Renal

Severe renal impairment: use with caution; initial doses as standard but maintenance may need reduction — monitor closely.

Hepatic

Moderate hepatic impairment: reduce doses by 50%. Severe hepatic impairment: reduce by 75%. Titrate slowly.

Paediatric weight-based calculator

BNFc: Licensed for epilepsy from age 2 years. For psychiatric indications: seek specialist child and adolescent psychiatry opinion. Titration schedule varies by concomitant medications — extremely complex in children.

Clinical pearls

  • SJS prevention: slow titration is non-negotiable — do not accelerate titration schedule even if patient is impatient. Any rash in first 8 weeks = stop immediately and do not rechallenge
  • COCP interaction is clinically significant: oestrogen in combined pill halves lamotrigine levels — breakthrough seizures or mood episodes may occur when pill is started. Dose must be increased. When pill is stopped, lamotrigine levels double — toxicity risk
  • Unlike lithium/valproate, lamotrigine does NOT treat acute mania — used solely for bipolar depression prevention and maintenance
  • Drug levels (monitoring): lamotrigine has a broad therapeutic range — plasma levels used to check adherence rather than guide dose

Contraindications

  • Hypersensitivity to lamotrigine
  • Previous SJS or toxic epidermal necrolysis with lamotrigine

Side effects

  • Rash — including Stevens-Johnson syndrome / toxic epidermal necrolysis (SJS/TEN): most serious; risk highest in first 8 weeks and with rapid titration or concomitant valproate
  • Headache, dizziness
  • Blurred vision, diplopia
  • Nausea
  • Insomnia
  • Tremor
  • Aseptic meningitis (rare — hypersensitivity)
  • Haemophagocytic lymphohistiocytosis (very rare)

Interactions

  • Valproate — doubles lamotrigine levels (inhibits glucuronidation); halve lamotrigine doses; SJS risk increased
  • Carbamazepine, phenytoin, rifampicin (enzyme inducers) — halve lamotrigine levels; double lamotrigine doses
  • COCP (hormonal contraceptives) — oestrogen reduces lamotrigine levels by ~50%; dose adjustment needed when starting/stopping pill; use barrier contraception as backup
  • Sertraline — modest increase in lamotrigine levels; monitor

Monitoring

  • Rash (first 8 weeks — critical)
  • Mood stability (bipolar symptom rating)
  • Drug levels (adherence checking)
  • LFTs and FBC if symptoms

Reference: BNFc; BNF 90; NICE CG185 (Bipolar Disorder); MHRA Lamotrigine Safety Update. Verify against your local formulary and the latest BNF before prescribing.

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Curated clinical cross-links plus same-class fallbacks.

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