Drug interactions between Lamictal and Mysoline

ADJUST DOSE: Coadministration with an enzyme-inducing antiepileptic agent such as carbamazepine, phenytoin, phenobarbital, or primidone may decrease the serum concentrations of lamotrigine. The mechanism is increased clearance due to induction of lamotrigine glucuronidation in the liver. Studies have found that enzyme-inducing antiepileptic agents can reduce lamotrigine serum concentrations by approximately 40%.

MANAGEMENT: When lamotrigine is added to existing therapy containing an enzyme-inducing antiepileptic agent without valproate, the initial dosage of lamotrigine should be 0.6 mg/kg/day in two divided doses (2 to 12 years of age) or 50 mg/day (older than 12 years of age) for the first 2 weeks. The initial dosage should be doubled for the next 2 weeks, then increased by 1.2 mg/kg/day or 100 mg/day every 1 to 2 weeks as needed and as tolerated. The usual maintenance dosage is 5 to 15 mg/kg/day (up to 400 mg/day) in children up to 12 years of age and 300 to 500 mg/day (400 mg/day for the treatment of bipolar disorder) in older patients. Patients should be advised to promptly notify their physician if they experience worsening of seizure control or increased adverse effects. A reevaluation of all antiepileptic agents in the regimen should be considered prior to making any changes. If the enzyme-inducing antiepileptic agent is discontinued, lamotrigine half-life will be prolonged and a dosage adjustment may be necessary. Prescribers should refer to the lamotrigine product labeling for complete dosing information.