In patients who are taking valproic acid in which it increases blood levels of lamotrigine, the initial dose of lamotrigine is 25 mg every other day for two weeks, then 25 mg once daily for two weeks. After 4 weeks the dose is slowly increased by 25 to 50 mg per day every one to two weeks until a dose of 100 to 400 mg once daily or divided twice daily is reached. The maintenance dose when using extended release tablets is 200 to 600 mg once daily.
The target dose for treating bipolar disorder is 100 to 400 mg daily.
DRUG INTERACTIONS: Lamotrigine can interact with valproic acid. When lamotrigine is initiated in patients already receiving valproic acid, the blood concentrations of valproic acid can decrease over a 3-week period. This may result in loss of seizure control. Valproic acid increases lamotrigine levels. The risk of severe skin rash may be increased by combining lamotrigine with valproic acid. There may be a higher incidence of dizziness, double vision, and blurred vision in patients receiving carbamazepine together with lamotrigine. The mechanism of this interaction is unclear.
Estrogen containing oral contraceptives, phenobarbitol, primidone, phenytoin, and rifampin reduce the blood levels of lamotrigine by 40%-50% by increasing the breakdown of lamotrigine in the liver. This may result in reduced efficacy if the dose of lamotrigine is not adjusted.
PREGNANCY: Use of lamotrigine during pregnancy has not been adequately evaluated.
NURSING MOTHERS: Lamotrigine is secreted into human breast milk. Because the effects on the infant are unknown, breastfeeding while taking lamotrigine is not recommended.
Medically reviewed by Eni Williams, PharmD
Reference: FDA Prescribing Information
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