Maximum Dosage of Lamotrigine (Lamictal)
The maximum recommended dosage of lamotrigine is 400mg/day for bipolar disorder and 600mg/day for epilepsy, typically administered in divided doses twice daily. 1
Dosing Guidelines by Indication
Epilepsy
- Standard maximum dose: 600mg/day
- Typical maintenance dose: 200-500mg/day in two divided doses
- Initial titration: Start low and increase slowly to minimize risk of serious rash
Bipolar Disorder
- Maximum dose: 400mg/day
- Typical maintenance dose: 100-200mg/day in 1-2 divided doses
Dosing Considerations Based on Concomitant Medications
Lamotrigine dosing must be adjusted based on other medications the patient is taking:
With enzyme inhibitors (e.g., valproic acid):
- Lower lamotrigine doses required
- Maximum dose may need to be reduced
With enzyme inducers (e.g., carbamazepine, phenytoin, phenobarbital):
- Higher lamotrigine doses may be required
- May still need to stay within the 600mg/day maximum
Titration Schedule
Proper titration is critical to minimize the risk of serious rash:
- Start with low dose (typically 25mg daily)
- Gradually increase over 6-8 weeks to target dose
- More rapid titration significantly increases risk of serious adverse effects
Special Populations
Elderly
- Lower doses are often effective and better tolerated
- In one study, a mean dose of 72mg/day was effective for elderly patients with epilepsy 2
Renal/Hepatic Impairment
- Dose reduction may be necessary
- More careful monitoring required
Safety Considerations
The most serious adverse effect is skin rash, which occurs in approximately 5% of patients, with Stevens-Johnson syndrome occurring in 0.1% 1. Other common side effects include:
- Headache
- Dizziness
- Drowsiness
- Nausea
- Ataxia and diplopia (particularly at higher doses)
Monitoring Recommendations
- Baseline complete blood count and liver function tests
- Periodic monitoring throughout treatment
- More frequent monitoring when adding or removing medications that affect lamotrigine metabolism
Clinical Pearls
- Exceeding recommended maximum doses increases risk of adverse effects without necessarily improving efficacy
- The risk of serious rash is significantly higher with rapid dose escalation
- Therapeutic blood levels are not well established, but a range of 1-4 mg/L has been proposed 3
- Some patients have tolerated concentrations >10 mg/L without clinical toxicity, but this is not recommended as standard practice 3
Lamotrigine's dosing should be carefully managed with attention to concomitant medications, patient characteristics, and monitoring for adverse effects, particularly during the initial titration period.