Adults

Dosage varies significantly based on indication and concomitant medications. Typically started at a low dose (e.g., 25 mg daily) and gradually titrated upwards over several weeks to a maintenance dose (e.g., 100-400 mg daily).

Elderly

Similar to adult dosing, but caution and slower titration may be required due to potential decreased renal or hepatic function.

Renal_impairment

Reduced maintenance dose may be necessary. Specific guidelines vary based on creatinine clearance.

Onset

Varies, typically several weeks for full therapeutic effect.

Excretion

Primarily renal (urine) as metabolites, with about 10% excreted unchanged.

Half life

Approximately 29 hours (range 14-103 hours), can be affected by co-administered drugs.

Absorption

Rapidly and completely absorbed after oral administration. Bioavailability is approximately 98%.

Metabolism

Primarily hepatic via glucuronidation.

Valproate

Increases lamotrigine levels by inhibiting its metabolism, requiring a significant dose reduction of lamotrigine.

Oral Contraceptives

May decrease lamotrigine levels, requiring dose adjustments.

Carbamazepine, Phenytoin, Phenobarbital, Primidone

Decrease lamotrigine levels by inducing its metabolism, requiring an increased lamotrigine dose.