Lamotrigine: Drug Information
1. Drug Name
Generic Name
Lamotrigine
Brand Name(s)
- Pakistan: Lamictal
- India: Lamitor
- US: Lamictal
- UK: Lamictal
2. Pharmacological Class
Class
Anticonvulsant
Subclass
Phenyltriazine
3. Mechanism of Action
Lamotrigine inhibits voltage-sensitive sodium channels, thereby stabilizing neuronal membranes and inhibiting the release of excitatory neurotransmitters such as glutamate and aspartate.
4. Indications
Primary Indications
- Epilepsy: Monotherapy or adjunctive therapy for partial onset seizures, primary generalized tonic-clonic seizures, and generalized seizures of Lennox-Gastaut syndrome.
- Bipolar Disorder: Maintenance treatment to delay the time to occurrence of mood episodes in patients treated for acute mood episodes with standard therapy.
Off-label Uses
- Trigeminal neuralgia
- Cluster headaches
- Migraine prophylaxis
- Depression
5. Dosage and Administration
Standard Dosage
For epilepsy:
- Initial: 25 mg once daily for 2 weeks, then 50 mg once daily for 2 weeks, followed by 100 mg/day in 1 or 2 divided doses
- Maintenance: 225-375 mg/day in 2 divided doses
For bipolar disorder:
- Initial: 25 mg once daily for 2 weeks, then 50 mg once daily for 2 weeks, followed by 100 mg/day
- Maintenance: 200 mg/day
Route of Administration
Oral (tablets, chewable/dispersible tablets, orally disintegrating tablets)
Special Populations
- Pediatric: Dosing varies by age and weight; monitor for increased risk of rash
- Geriatric: Dose adjustments may be necessary based on renal and hepatic function
6. Pharmacokinetics
Absorption
Lamotrigine is rapidly and completely absorbed after oral administration, with peak plasma concentrations occurring 1.4 to 4.8 hours post-dose.
Distribution
Lamotrigine is approximately 55% bound to plasma proteins.
Metabolism
Lamotrigine is primarily metabolized in the liver through glucuronidation.
Excretion
Lamotrigine is primarily excreted in the urine as glucuronide metabolites, with a small percentage excreted unchanged.
Half-life
The elimination half-life of lamotrigine is approximately 29 hours in healthy adults.
7. Contraindications
- Hypersensitivity to lamotrigine or any of its components
8. Warnings and Precautions
- Serious skin rashes, including Stevens-Johnson syndrome and toxic epidermal necrolysis
- Increased risk of suicidal thoughts and behavior
- Aseptic meningitis
- Blood dyscrasias, including neutropenia and thrombocytopenia
- Avoid abrupt discontinuation to prevent seizure recurrence
9. Side Effects
Common Side Effects
- Dizziness
- Headache
- Blurred vision
- Nausea
- Insomnia
Serious Side Effects
- Severe skin reactions
- Suicidal thoughts and behaviors
- Aseptic meningitis
- Blood disorders
10. Drug Interactions
Major Interactions
- Valproic acid: Increases lamotrigine levels and risk of serious skin reactions
- Carbamazepine: Decreases lamotrigine levels
Moderate Interactions
- Oral contraceptives: May reduce the efficacy of lamotrigine
- Rifampin: Decreases lamotrigine levels
Minor Interactions
- Paracetamol: Potential for altered efficacy
11. Pregnancy and Lactation
Pregnancy Category
Category C - Risk cannot be ruled out. Lamotrigine can cause fetal harm when administered to pregnant women.
Breastfeeding Considerations
Lamotrigine is excreted in human milk. Caution is advised when administered to a nursing woman.
12. Patient Counseling Information
- Take lamotrigine exactly as prescribed and do not exceed the recommended dose.
- Lamotrigine may cause dizziness and drowsiness; avoid driving or operating heavy machinery until you know how it affects you.
- Inform your healthcare provider about all medications you are taking