- There is a significant synergistic drug interaction with valproate (valproate is an enzyme inhibitor, lamotrigine clearance is reduced and thus lamotrigine levels are higher).
- This can increase risk of rash significantly.
- Lower doses of lamotrigine and slow escalation are required.
A reasonable dosage regime is commencement of lamotrigine 0.15mg/kg/second daily (for a week), then same dose daily (for 2 weeks), then increase every 2 weeks by 0.15mg/kg/day to target 1-3mg/kg/day. Maximal dose 4mg/kg/day.
- Adding lamotrigine to valproate does not appear to affect valproate levels.
- On lamotrigine, a recommended maximum dose of valproate is approximately 30mg/kg.
- Dosages per kilogram can only be used in children of weight approximately up to 30-40kgs.
- Consult appropriate formularies for children with higher weights and in the adult range.
- These dosages are only a guide and appropriate formularies should be consulted as needed and tailored to the patient by the primary physician.
- All anticonvulsants are potentially teratogenic and this is often dose-related (see section: AED Prescribing - Pregnancy)
- For a complete list of adverse effects, appropriate formularies should be consulted.
Interactions | Precautions
- Oral contraceptives and the other anticonvulsants that induce hepatic glucuronidation will also decrease the level of lamotrigine.