LAMICTAL CD
Clinical safety rating: caution
Comprehensive clinical and safety monograph for LAMICTAL CD (LAMICTAL CD).
Lamotrigine is a phenyltriazine anticonvulsant that stabilizes neuronal membranes by blocking voltage-sensitive sodium channels and inhibiting the presynaptic release of excitatory neurotransmitters such as glutamate and aspartate.
| Metabolism | Lamotrigine is primarily metabolized via glucuronidation by UGT1A4, with minor involvement of UGT2B7. It is not extensively metabolized by CYP450 enzymes. |
| Excretion | Lamotrigine is primarily eliminated by hepatic metabolism, with approximately 94% of the dose excreted in urine as glucuronide conjugates (10% as unchanged drug) and 2% in feces. |
| Half-life | Terminal elimination half-life in adults is approximately 25.4 hours (range 14-50 hours) in healthy volunteers; reduced to 14.5 hours (range 12-20) with enzyme-inducing antiepileptics (e.g., carbamazepine, phenytoin), increased to 59 hours (range 30-90) with valproate, and prolonged in renal impairment. |
| Protein binding | Approximately 55% bound to plasma proteins (albumin); binding is not concentration-dependent and is unlikely to cause significant drug interactions via displacement. |
| Volume of Distribution | Volume of distribution is approximately 1.0-1.4 L/kg (range 0.6-2.0 L/kg), indicating extensive distribution into tissues and consistent with a moderate Vd. |
| Bioavailability | Oral: Bioavailability is nearly 98% for the chewable dispersible tablets (Lamictal CD) when administered with or without food; no significant first-pass effect. |
| Onset of Action | Oral: Time to peak concentration is 1.5-4 hours; clinical effects (e.g., seizure frequency reduction) may be observed within 2-4 weeks of dose titration. |
| Duration of Action | Oral: Antiepileptic effect persists for 12-24 hours after a single dose; steady-state concentrations are achieved within 3-5 days without enzyme inducers or within 10-14 days with chronic dosing. Dosing frequency is typically twice daily. |
Lamotrigine extended-release (LAMICTAL CD) for epilepsy: initial 50 mg orally once daily for 2 weeks, then 100 mg once daily for 2 weeks, then 200 mg once daily for 2 weeks, then 300 mg once daily for 2 weeks, then 400 mg once daily thereafter. For bipolar disorder: initial 25 mg once daily for 2 weeks, then 50 mg once daily for 2 weeks, then 100 mg once daily for 2 weeks, then 200 mg once daily thereafter.
| Dosage form | TABLET, FOR SUSPENSION |
| Renal impairment | GFR 30-89 mL/min: no adjustment needed. GFR <30 mL/min: reduce maintenance dose by 25-50%. Hemodialysis: administer dose after dialysis; consider supplemental dose of 50-100 mg after session. |
| Liver impairment | Child-Pugh class A: reduce dose by 25%. Child-Pugh class B: reduce dose by 50%. Child-Pugh class C: reduce dose by 75% and titrate slowly. |
| Pediatric use | Epilepsy adjunctive therapy (2-12 years): weight-based dosing. Patients on valproate: 0.15 mg/kg/day once daily for 2 weeks, then 0.3 mg/kg/day once daily for 2 weeks, then increase by 0.3 mg/kg/day every 1-2 weeks up to maintenance of 1-5 mg/kg/day. Patients on enzyme-inducing AEDs but not valproate: 0.6 mg/kg/day once daily for 2 weeks, then 1.2 mg/kg/day once daily for 2 weeks, then increase by 1.2 mg/kg/day every 1-2 weeks up to maintenance of 5-15 mg/kg/day. Patients not on valproate or enzyme-inducing AEDs: 0.3 mg/kg/day once daily for 2 weeks, then 0.6 mg/kg/day once daily for 2 weeks, then increase by 0.6 mg/kg/day every 1-2 weeks up to maintenance of 4.5-7.5 mg/kg/day. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for LAMICTAL CD (LAMICTAL CD).
| Breastfeeding | Lamotrigine is excreted into breast milk with a milk-to-plasma ratio (M/P) of approximately 0.6. Relative infant dose is about 35-50% of maternal weight-adjusted dose. Monitor infant for rash, drowsiness, poor feeding, and thrombocytopenia. Benefits of breastfeeding generally outweigh risks if maternal dose is moderate and infant is healthy. |
| Teratogenic Risk | Lamotrigine is associated with an increased risk of oral clefts (cleft lip/palate) and other congenital malformations (e.g., hypospadias, neural tube defects) when used in the first trimester. The risk appears dose-dependent. Second and third trimester exposure may be associated with impaired fetal growth and neurodevelopmental effects. Late pregnancy exposure may lead to neonatal withdrawal or toxicity (e.g., hypotonia, poor feeding). |
■ FDA Black Box Warning
Lamotrigine can cause serious rashes requiring hospitalization and discontinuation. The risk is increased in pediatric patients (0.3-0.8% vs 0.08-0.3% in adults), with co-administration of valproate, exceeding recommended initial dose, or exceeding recommended dose escalation. Rash may be life-threatening, including Stevens-Johnson syndrome, toxic epidermal necrolysis, and DRESS syndrome.
| Serious Effects |
Hypersensitivity to lamotrigine or any component of the formulation; use of a dose escalation schedule exceeding recommended guidelines (due to increased risk of serious rash).
| Precautions | Serious rashes (including SJS, TEN, DRESS), aseptic meningitis, hemophagocytic lymphohistiocytosis, hypersensitivity reactions, cardiac rhythm abnormalities (dose-dependent prolongation of PR interval and QRS duration), blood dyscrasias, suicidal thoughts and behaviors, withdrawal seizures upon abrupt discontinuation, and risks during pregnancy (cleft palate, other malformations). |
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| Geriatric use | Start at lower end of dosing range due to age-related reduced clearance. Titrate slowly. Monitor for dizziness, ataxia, and rash. Consider starting at 25 mg every other day for 2 weeks, then 25 mg once daily for 2 weeks, then 50 mg once daily for 2 weeks, then 100 mg once daily for 2 weeks, then 150 mg once daily for 2 weeks, then 200 mg once daily thereafter. |
| Fetal Monitoring | Monitor lamotrigine serum concentrations every 2-4 weeks during pregnancy and postpartum. Assess fetal anatomy via ultrasound for clefts and malformations. Monitor fetal growth in second and third trimesters. Newborn assessment for withdrawal symptoms, rash, and hyperbilirubinemia. |
| Fertility Effects | Lamotrigine has not been shown to significantly impair fertility in humans. Animal studies show no adverse effects on fertility. However, it may reduce serum folate levels, and folate deficiency is linked to infertility and neural tube defects; supplementation is recommended. |