The appropriate dosages of Lamictal depend on what other AEDs, if any, the patient is taking. If Lamictal is used as monotherapy for young adults, the starting dose is 25 mg a day, increased every two weeks by 25 mg daily as needed, usually to 100-200 mg a day.

For young adults who are taking hepatic enzyme–inducing AEDs, however, Lamictal is usually started at 25 mg twice a day. Every 1-2 weeks, the amount can be increased by 50 mg per day as required (if side effects are not troublesome) to a target dose of 300-500 mg per day. The AEDs that require these higher dosages of Lamictal are:

• carbamazepine (Tegretol, Tegretol-XR, Carbatrol)
• phenytoin (Dilantin, Phenytek)
• phenobarbital)
• primidone (Mysoline)

For adults taking valproate (Depakote, Depakote ER, valproic acid), the initial dose is 12.5 to 25 mg every other day, with increases of 25 mg per day every two weeks as needed and tolerated, usually to 150-200 mg daily.

Patients over age 65 generally require a lower initial dose and lower target maintenance dose.

Measurements of serum concentrations are useful, particularly if the patient stops or starts enzyme-inducing AEDs or valproate. Therapeutic serum concentrations of lamotrigine have not been established, but generally levels of 5-15 mcg/mL are achieved.

• Algorithm for dosing lamotrigine (Lamictal)
• Algorithm for adding lamotrigine to valproate
• Algorithm for adding valproate to lamotrigine