Maximum Dosing of Lamotrigine (Lamictal)
The maximum dose of lamotrigine is 500 mg/day for epilepsy, with typical maintenance dosing of 200-300 mg/day, and 200 mg/day for bipolar disorder. 1, 2, 3
Standard Maximum Dosing by Indication
Epilepsy
- Maximum dose: 500 mg/day for adjunctive therapy in adults with partial seizures 4
- Typical effective maintenance range: 100-500 mg/day 1
- Most patients respond to 200-300 mg/day in clinical practice 4, 5
Bipolar Disorder
- Target maintenance dose: 200 mg/day after 6-week titration 2, 3
- This is the standard therapeutic dose, not typically exceeded 1
Available Formulations
The FDA-approved extended-release formulations include tablets up to 300 mg, with available strengths of 25 mg, 50 mg, 100 mg, 200 mg, 250 mg, and 300 mg 6. This indicates that doses up to 300 mg can be given as a single tablet, though higher total daily doses may require multiple tablets.
Critical Dosing Considerations
Dose Adjustments for Drug Interactions
- With valproate: Lamotrigine doses must be reduced by approximately 50% due to inhibition of lamotrigine metabolism 2, 3
- With carbamazepine: Higher lamotrigine doses may be required due to enzyme induction 2, 3
Titration Requirements
- Slow titration is mandatory to minimize risk of serious rash, including Stevens-Johnson syndrome 1, 2, 3
- Standard starting dose: 25 mg once daily for first two weeks 1
- Titration occurs over 6 weeks to reach 200 mg/day target 2, 3
- Never exceed recommended dose escalation rates 1
Therapeutic Monitoring
- Therapeutic plasma level range: 1-4 mg/L 1
- Monitoring recommended for suspected malabsorption, poor treatment response, or significant drug interactions 1
- Unlike lithium, routine serum level monitoring is generally not required 2, 3
Common Pitfall
If lamotrigine has been discontinued for more than 5 days, do not restart at the full maintenance dose—re-titration from 25 mg is required to minimize rash risk 1. The exception is discontinuation of less than 5 days in patients with no history of rash or intolerance, where a loading dose of 6.5 mg/kg may be considered 1.