Anticonvulsant (Sodium Channel Blocker) Pregnancy: Large data (>12,700 pregnancies) do not indicate an increased risk of major congenital malformations at maintenance doses; use the lowest effective dose (a dose-related risk signal was seen at >=325 mg/day). Folic acid supplementation advised. Monitor serum levels before/during/after pregnancy (levels may fall in pregnancy and rise after birth). Do not stop AED therapy abruptly.

Lamotrigine

Brand names: Lamictal

Lamotrigine is an antiepileptic used for focal and generalised seizures and as a mood stabiliser in bipolar disorder.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 100-200 mg/day (usual maintenance, monotherapy)

Route: Oral (tablets swallowed whole; may be halved but not chewed/crushed)

Frequency: Once daily or in two divided doses (maintenance)

Epilepsy, adults and adolescents aged 13 years and above. Because of rash risk the initial dose and dose escalation must not be exceeded. Monotherapy: 25 mg/day (weeks 1-2), 50 mg/day (weeks 3-4), then increase by max 50-100 mg every 1-2 weeks to usual maintenance 100-200 mg/day (up to 500 mg/day required in some patients). Adjunctive WITH valproate: 12.5 mg/day (25 mg on alternate days) weeks 1-2, 25 mg/day weeks 3-4, maintenance 100-200 mg/day. Adjunctive WITHOUT valproate but WITH glucuronidation inducers (phenytoin, carbamazepine, phenobarbitone, primidone, rifampicin, lopinavir/ritonavir): 50 mg/day weeks 1-2, 100 mg/day (two divided doses) weeks 3-4, maintenance 200-400 mg/day (up to 700 mg/day in some). Adjunctive WITHOUT valproate and WITHOUT inducers: 25 mg/day weeks 1-2, 50 mg/day weeks 3-4, maintenance 100-200 mg/day. If restarting after discontinuation beyond five half-lives, re-escalate from the initial dose. Paediatric (2-12 years) dosing is weight-based - see the paediatric record.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Dosing is based on concomitant medications, indication, and patient age. ( 2.1 , 2.2 , 2.3 , 2.4 ) To avoid an increased risk of rash, the recommended initial dose and subsequent dose escalations should not be exceeded. Lamotrigine Orally Disintegrating Tablets Patient Titration Kits are available for the first 5 weeks of treatment. ( 2.1 , 16 ) Do not restart lamotrigine orally disintegrating tablets in patients who discontinued due to rash unless the potential benefits clearly outweigh the risks. ( 2.1 , 5.1 ) Adjustments to maintenance doses will be necessary in most patients starting or stopping estrogen-containing products, including oral contraceptives. ( 2.1 , 5.9 ) Discontinuation: …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2026-04-22. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Hypersensitivity to lamotrigine, sunset yellow aluminium lake, or any of the excipients

Side effects

Skin rash (very common) — including rare/very rare serious rashes: Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS/hypersensitivity syndrome
Headache (very common)
Somnolence, dizziness, tremor, insomnia (common)
Nausea, vomiting, diarrhoea (common)
Aggression, irritability (common)

Interactions

Valproate — inhibits lamotrigine glucuronidation and raises lamotrigine levels; use the lower valproate-specific titration and maintenance dosing
Enzyme-inducing drugs — phenytoin, carbamazepine, phenobarbitone, primidone, rifampicin, lopinavir/ritonavir induce glucuronidation and lower lamotrigine levels; use the higher inducer-specific titration
Estrogen-containing oral contraceptives — increase lamotrigine clearance; maintenance dose may need increasing (US labelling)

Clinical monograph

How it works

It stabilises neuronal membranes mainly by blocking voltage-gated sodium channels, reducing excitatory neurotransmitter release.

Prescribing in practice

Serious rashes (including Stevens-Johnson syndrome) can occur, especially with rapid escalation or when combined with valproate — titrate slowly and stop for any significant rash.
Valproate markedly raises lamotrigine levels (use a lower lamotrigine dose); enzyme inducers lower them.
Do not stop abruptly; levels may fall in pregnancy and need review.

Monitoring

Watch for rash during titration; review seizure/mood control; consider levels around pregnancy.

Counselling the patient

Increase the dose slowly, exactly as instructed.
Report any rash immediately, particularly in the first weeks.
Do not stop suddenly.

Evidence & guidelines

A first-line option for focal epilepsy and some generalised seizures, and a maintenance treatment in bipolar depression, with a key rash/titration caution.

Reference: NICE NG217; Lamictal SPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways