Lamotrigine (Lamictal)
lamotrigine
Indications
| Indication | Approved Population | Therapy Type | Status |
|---|---|---|---|
| Partial-onset seizures | ≥2 years | Adjunctive | FDA Approved |
| Primary generalized tonic-clonic seizures | ≥2 years | Adjunctive | FDA Approved |
| Generalized seizures of Lennox-Gastaut syndrome | ≥2 years | Adjunctive | FDA Approved |
| Partial-onset seizures — conversion to monotherapy | ≥16 years | Monotherapy (conversion from CBZ, PHT, PB, primidone, or VPA) | FDA Approved |
| Bipolar I disorder — maintenance | Adults | Monotherapy or adjunctive (delays mood episodes) | FDA Approved |
Lamotrigine is a broad-spectrum antiepileptic drug and mood stabiliser with dual indications in epilepsy and bipolar I disorder. In epilepsy it is effective across focal and generalised seizure types and is one of the few AEDs with robust evidence for Lennox-Gastaut syndrome. In bipolar disorder, lamotrigine is used exclusively for maintenance treatment to delay mood episodes — it has no established efficacy for acute mania, mixed episodes, or acute depression at standard doses.
Unipolar depression (treatment-resistant) — Used as augmentation to antidepressants in refractory major depressive disorder. Evidence quality: Low–Moderate (small RCTs with mixed results; no FDA approval).
Neuropathic pain / trigeminal neuralgia — Small controlled trials suggest benefit in trigeminal neuralgia and central post-stroke pain. Evidence quality: Low (insufficient evidence per Cochrane 2013 review; not recommended in most neuropathic pain guidelines).
Dosing
Lamotrigine dosing varies dramatically based on whether the patient is taking valproate (which doubles lamotrigine levels), enzyme-inducing AEDs (carbamazepine, phenytoin, phenobarbital, primidone — which halve lamotrigine levels), or neither. Using the wrong titration schedule is the most common cause of serious rash. Always verify concomitant medication status before prescribing.
Epilepsy — Adjunctive Therapy (Adults and Adolescents >12 Years)
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Adjunctive with valproate (VPA) | 25 mg every other day × 2 wk, then 25 mg daily × 2 wk | 100–200 mg/day | 200 mg/day | Increase by 25–50 mg/day q1–2 wk from week 5 VPA inhibits glucuronidation; doubles LTG levels |
| Adjunctive without VPA or enzyme inducers | 25 mg daily × 2 wk, then 50 mg daily × 2 wk | 225–375 mg/day | 375 mg/day | Increase by 50 mg/day q1–2 wk from week 5 Give in 2 divided doses |
| Adjunctive with enzyme inducers (CBZ, PHT, PB, primidone) without VPA | 50 mg daily × 2 wk, then 100 mg/day × 2 wk | 300–500 mg/day | 500 mg/day | Increase by 100 mg/day q1–2 wk from week 5 Give in 2 divided doses; enzyme inducers reduce LTG ~40% |
| Conversion to monotherapy (from inducer) | Achieve 500 mg/day per adjunctive schedule, then taper concomitant AED by 20%/wk over 4 weeks | 500 mg/day | Target monotherapy dose is 500 mg/day in 2 divided doses FDA PI Table 4 provides VPA conversion steps separately | |
Bipolar I Disorder — Maintenance (Adults)
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Bipolar maintenance with valproate | 25 mg QOD × 2 wk → 25 mg daily × 2 wk → 50 mg × 1 wk | 100 mg/day | 100 mg/day | Very slow titration essential Target reached at week 6 |
| Bipolar maintenance without VPA or inducers | 25 mg daily × 2 wk → 50 mg daily × 2 wk → 100 mg × 1 wk | 200 mg/day | 200 mg/day | No additional benefit demonstrated above 200 mg/day Target reached at week 6 |
| Bipolar maintenance with enzyme inducers, no VPA | 50 mg daily × 2 wk → 100 mg daily × 2 wk → 200 mg × 1 wk | up to 400 mg/day | 400 mg/day | Give in divided doses Target reached at week 7 |
Hepatic Impairment Dosing
| Hepatic Function | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Mild (Child-Pugh A) | No adjustment needed | Standard dosing per indication | ||
| Moderate or severe without ascites | Reduce initial, escalation, and maintenance doses by ~25% | Adjust based on clinical response | ||
| Severe with ascites | Reduce initial, escalation, and maintenance doses by ~50% | Adjust based on clinical response | ||
If lamotrigine has been stopped for more than 5 half-lives (which varies by concomitant medications — approximately 3 days with enzyme inducers, 5–7 days as monotherapy, or 10–12 days with valproate), restart from the initial titration schedule. This is critical because rapid re-titration after a gap increases the risk of serious rash.
Pharmacology
Mechanism of Action
Lamotrigine stabilises neuronal membranes by blocking voltage-sensitive sodium channels in a use- and voltage-dependent manner, thereby inhibiting the presynaptic release of excitatory neurotransmitters, principally glutamate. This selective reduction in pathological high-frequency firing — while preserving normal neuronal activity — underlies both its antiepileptic and mood-stabilising properties. Lamotrigine also has weak inhibitory effects on 5-HT3 receptors and high-voltage-activated calcium channels (N- and P/Q-type), though the clinical significance of these secondary actions is not fully established. Unlike many conventional AEDs, lamotrigine does not meaningfully interact with GABA receptors or alter GABA levels in the brain.
ADME Profile
| Parameter | Value | Clinical Implication |
|---|---|---|
| Absorption | Bioavailability ~98%; Tmax ~2.5 h (range 1.4–4.8 h); not affected by food; no first-pass metabolism | Rapid and nearly complete absorption; can be taken with or without food |
| Distribution | Vd 0.9–1.3 L/kg; protein binding ~55%; crosses placenta (cord:maternal ratio ~1.0); breast milk:serum ratio ~0.6 | Moderate tissue penetration; brain concentrations approximate total plasma levels; significant placental transfer |
| Metabolism | Primarily UGT1A4-mediated glucuronidation; major metabolite is inactive 2-N-glucuronide (76% of dose); minor 5-N-glucuronide (10%); no significant CYP450 involvement | Half-life dramatically altered by UGT inducers (CBZ, PHT, OCP) and inhibitors (VPA); dosing must account for concomitant medications |
| Elimination | t½: 25–33 h monotherapy; 14–15 h with enzyme inducers; 48–59 h with VPA; ~86% excreted in urine as metabolites; ~10% unchanged | Steady state: ~5 days monotherapy, ~3 days with inducers, ~10 days with VPA; taper over ≥2 weeks to discontinue |
Side Effects
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Dizziness | 38% | Dose-related; more common with concomitant carbamazepine; often improves with dose adjustment |
| Headache | 29% | Comparable to placebo in some trials; rarely requires discontinuation |
| Diplopia | 28% | Dose-related; significantly higher with concomitant CBZ (pharmacodynamic interaction) |
| Ataxia | 22% | Dose-related; assess fall risk in elderly; often improves at lower doses |
| Nausea | 19% | Dose-related; take with food if troublesome |
| Blurred vision | 16% | Dose-related; more frequent with CBZ co-administration |
| Somnolence | 14% | Less sedating than many AEDs; some patients report an alerting effect |
| Rash (non-serious) | ~10% | Most rashes are benign maculopapular; cannot reliably distinguish from serious rash — discontinue at first sign |
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Vomiting | 9% | Dose-related; frequently resolves with continued treatment |
| Insomnia | 6% | Can reflect alerting effect; consider AM dosing if problematic |
| Tremor | 4% | Usually mild postural tremor; differentiate from underlying condition |
| Depression | 4% | Monitor in bipolar patients; suicidality screening at each visit |
| Anxiety | 4% | May be indication-related rather than drug-related |
| Coordination abnormality | 4% | Overlaps with ataxia; assess driving safety |
| Adverse Effect | Estimated Frequency | Typical Onset | Required Action |
|---|---|---|---|
| Stevens-Johnson syndrome / TEN | 0.08–0.3% adults; 0.3–0.8% pediatric | 2–8 weeks (nearly all cases) | Discontinue immediately at first sign of rash unless clearly not drug-related; do not rechallenge |
| DRESS / Multiorgan hypersensitivity | Rare; fatalities reported (2/3,796 adults; 4/2,435 pediatric in trials) | Weeks after initiation | Discontinue if no alternative etiology; presents with fever, rash, lymphadenopathy, organ involvement |
| Hemophagocytic lymphohistiocytosis (HLH) | Very rare (postmarketing) | 8–24 days | Evaluate immediately for extreme systemic inflammation (high ferritin, cytopenias, hepatosplenomegaly); discontinue |
| Cardiac conduction abnormalities | Risk in patients with structural heart disease (in vitro Na channel blockade) | Variable | Weigh benefit vs arrhythmia risk in patients with clinically significant cardiac disease |
| Blood dyscrasias (neutropenia, thrombocytopenia, pancytopenia) | Rare | Variable | Monitor for unexpected infection, bruising, or bleeding; obtain CBC |
| Aseptic meningitis | Rare (postmarketing) | 1 day to 6 weeks | Discontinue; symptoms include headache, fever, nuchal rigidity, photophobia; recurs rapidly on rechallenge |
| Suicidality (AED class effect) | 0.43% (vs 0.24% placebo) | As early as 1 week | Monitor for emergence of depression, suicidal thoughts, mood changes |
Rash is the single most important safety concern with lamotrigine. Risk is highest with rapid dose escalation, concomitant valproate (1% hospitalisation rate with VPA vs 0.16% without), and in pediatric patients (0.3–0.8%). All rashes should be treated as potentially serious until proven otherwise — there is no reliable way to distinguish benign from dangerous rashes at onset. Patients should be instructed to contact their prescriber immediately upon noticing any skin change.
Drug Interactions
Lamotrigine is metabolised almost exclusively by UGT-mediated glucuronidation. It does not significantly induce or inhibit CYP450 enzymes. However, its clearance is profoundly affected by drugs that induce or inhibit UGT, making concomitant medication status the primary determinant of dosing. Lamotrigine also inhibits organic cation transporter 2 (OCT2), which may affect renal clearance of OCT2 substrates.
Monitoring
-
Skin / Rash
First 8 weeks intensively
Routine Instruct patients and caregivers to report ANY rash immediately. Nearly all life-threatening rashes occur within the first 2–8 weeks. Discontinue at first sign of rash unless clearly not drug-related. Risk factors: concomitant VPA, exceeding recommended titration rate, HLA-B*1502 allele (Han Chinese and Thai ancestry). -
Mood / Suicidality
Each visit
Routine Assess for new or worsening depression, suicidal ideation, and clinical worsening of bipolar disorder. AED class warning applies. Particularly important during titration and dose changes. -
Hepatic Function
Baseline; if symptomatic
Trigger-based Isolated liver failure and hepatic failure as part of multiorgan hypersensitivity have been reported. Obtain LFTs if patient develops signs suggestive of hepatic dysfunction (jaundice, dark urine, fatigue, anorexia). -
Lamotrigine Levels
Concomitant medication changes; pregnancy
Trigger-based No established therapeutic range. However, TDM is useful when adding or removing drugs affecting UGT (especially VPA, OCP, enzyme inducers) and during pregnancy (clearance increases up to 2-fold). Proposed reference range: 3–14 mcg/mL (epilepsy). -
CBC
If symptomatic
Trigger-based Blood dyscrasias (neutropenia, thrombocytopenia, pancytopenia) may occur with or without hypersensitivity syndrome. Monitor for signs of anemia, unexpected infection, or bleeding. -
HLA-B*1502 Testing
Before initiation (specific populations)
Trigger-based Consider HLA-B*1502 testing in patients of Han Chinese or Thai ancestry before starting lamotrigine. Positive allele status confers 2–3-fold increased risk of SJS/TEN. However, genotyping has limitations and should not replace clinical vigilance.
Contraindications & Cautions
Absolute Contraindications
- Known hypersensitivity to lamotrigine or any formulation ingredient — including prior SJS/TEN, angioedema, acute urticaria, extensive pruritus, or mucosal ulceration attributed to lamotrigine
Relative Contraindications (Specialist Input Recommended)
- Prior rash with lamotrigine (non-serious) — Do not restart unless benefits clearly outweigh risks; if restarting, use initial titration schedule regardless of previous dose
- Clinically significant structural or functional heart disease — In vitro data show lamotrigine inhibits cardiac sodium channels; could cause serious arrhythmias in patients with underlying cardiac disorders (FDA PI Section 5.4; added to labelling based on in vitro data)
- HLA-B*1502 positive status — 2–3-fold increased risk of SJS/TEN; weigh risks vs benefits carefully
Use with Caution
- Concomitant valproate — Doubles lamotrigine levels and increases serious rash risk; requires special dosing schedule
- Hepatic impairment (moderate/severe) — Dose reduction required; half-life can extend to 100 hours with severe disease plus ascites
- Renal impairment (significant) — Limited data; reduced maintenance doses may be appropriate; use with caution in severe renal impairment
- Pregnancy — Clearance may increase up to 2-fold during pregnancy; levels should be monitored; animal data suggest potential fetal harm
Lamotrigine can cause serious rashes requiring hospitalisation and discontinuation of treatment. The incidence is approximately 0.3–0.8% in pediatric patients (aged 2–17 years) and 0.08–0.3% in adults. One rash-related death occurred in a prospectively followed cohort of 1,983 pediatric patients. Rare cases of TEN and rash-related death have been reported in postmarketing experience. Risk factors include concomitant valproate, exceeding recommended initial dose or dose escalation rate, and HLA-B*1502 allele. Nearly all life-threatening rashes occur within 2–8 weeks of treatment initiation. Discontinue at the first sign of rash unless the rash is clearly not drug-related.
Patient Counselling
Purpose of Therapy
Lamotrigine helps control seizures or stabilise mood by reducing abnormal electrical activity in the brain. For epilepsy, it reduces the frequency and severity of seizures. For bipolar disorder, it helps prevent future episodes of depression and mania when taken consistently as a maintenance treatment — it is not used to treat acute mood episodes.
How to Take
Lamotrigine can be taken with or without food. The dose must be increased very slowly over several weeks according to a specific schedule provided by the prescriber. Do not increase the dose faster than instructed, even if seizures continue, as doing so significantly increases the risk of a serious skin reaction. Tablets should be swallowed whole; chewable tablets can be chewed, dissolved in water, or swallowed whole. Always visually inspect tablets to confirm you have received the correct medication and strength — medication mix-ups with similarly named drugs have been reported.
Sources
- GlaxoSmithKline. LAMICTAL (lamotrigine) prescribing information. Revised 10/2025. Reference ID: 5675542. FDA Label Primary regulatory source for all indications, dosing tables, adverse reactions, boxed warning, and pharmacokinetics cited in this monograph.
- GlaxoSmithKline. LAMICTAL XR (lamotrigine) extended-release tablets prescribing information. GSK PI Extended-release formulation PI; approved for partial-onset seizures in patients 13 years and older, and PGTC in patients 13 years and older with idiopathic generalized epilepsy.
- Messenheimer J, Mullens EL, Giorgi L, et al. Safety review of adult clinical trial experience with lamotrigine. Drug Saf. 1998;18(4):281–296. DOI Comprehensive safety review of lamotrigine across clinical trials including rash incidence data and discontinuation rates.
- Bowden CL, Calabrese JR, Sachs G, et al. A placebo-controlled 18-month trial of lamotrigine and lithium maintenance treatment in recently manic or hypomanic patients with bipolar I disorder. Arch Gen Psychiatry. 2003;60(4):392–400. DOI Pivotal RCT establishing lamotrigine efficacy for bipolar I maintenance, demonstrating delay in time to intervention for mood episodes.
- Calabrese JR, Bowden CL, Sachs G, et al. A placebo-controlled 18-month trial of lamotrigine and lithium maintenance treatment in recently depressed patients with bipolar I disorder. J Clin Psychiatry. 2003;64(9):1013–1024. DOI Companion pivotal trial to Bowden 2003, focusing on recently depressed bipolar I patients; demonstrated delay in depressive episodes.
- Brodie MJ, Richens A, Yuen AW. Double-blind comparison of lamotrigine and carbamazepine in newly diagnosed epilepsy. Lancet. 1995;345(8948):476–479. DOI Head-to-head trial demonstrating comparable efficacy to carbamazepine in newly diagnosed epilepsy with superior tolerability.
- Glauser T, Ben-Menachem E, Bourgeois B, et al. Updated ILAE evidence review of antiepileptic drug efficacy and effectiveness as initial monotherapy for epileptic seizures and syndromes. Epilepsia. 2013;54(3):551–563. DOI ILAE guideline supporting lamotrigine as a first-line option for initial monotherapy in focal and generalised seizures.
- Yatham LN, Kennedy SH, Parikh SV, et al. Canadian Network for Mood and Anxiety Treatments (CANMAT) and International Society for Bipolar Disorders (ISBD) 2018 guidelines for the management of patients with bipolar disorder. Bipolar Disord. 2018;20(2):97–170. DOI International guideline recommending lamotrigine as a first-line maintenance agent for bipolar I disorder, particularly for preventing depressive episodes.
- Xie X, Lancaster B, Bhatt K, et al. Interaction of the antiepileptic drug lamotrigine with recombinant rat brain type IIA Na+ channels and with native Na+ channels in rat hippocampal neurones. Pflugers Arch. 1995;430(3):437–446. DOI Key mechanistic study demonstrating use-dependent sodium channel blockade as the primary mechanism of action of lamotrigine.
- Rambeck B, Wolf P. Lamotrigine clinical pharmacokinetics. Clin Pharmacokinet. 1993;25(6):433–443. DOI Comprehensive PK review establishing key pharmacokinetic parameters including half-life variability with concomitant AEDs.
- Garnett WR. Lamotrigine: pharmacokinetics. J Child Neurol. 1997;12(Suppl 1):S10–S15. DOI Detailed review of lamotrigine PK in adults and children, including effects of enzyme inducers and inhibitors on half-life.
- Pennell PB, Peng L, Newport DJ, et al. Lamotrigine in pregnancy: clearance, therapeutic drug monitoring, and seizure frequency. Neurology. 2008;70(22 Pt 2):2130–2136. DOI Key study demonstrating up to 2-fold increase in lamotrigine clearance during pregnancy, supporting the need for therapeutic drug monitoring.
- Sabers A, Buchholt JM, Uldall P, et al. Lamotrigine plasma levels reduced by oral contraceptives. Epilepsy Res. 2001;47(1-2):151–154. DOI Study documenting the ~50% reduction in lamotrigine levels caused by estrogen-containing oral contraceptives.