Adults

Highly individualized. Typically starting with 25 mg daily for 2 weeks, then 50 mg daily for 2 weeks, then gradually increased. Maintenance dose usually 100-400 mg/day in 1-2 divided doses, depending on co-medications.

Elderly

No specific dose adjustment for elderly patients is generally required unless there is significant renal or hepatic impairment. Dosage titration should be done carefully.

Renal_impairment

Reduced maintenance doses may be required for severe impairment. Initial doses should be based on standard guidelines with caution.

Onset

Variable, often takes several weeks to achieve therapeutic levels due to gradual titration.

Excretion

Primarily renal (approximately 94% excreted in urine as metabolites).

Half life

Approximately 25-33 hours (can be reduced with enzyme-inducing antiepileptic drugs or increased with valproate).

Absorption

Rapidly and completely absorbed from the gastrointestinal tract. Peak plasma concentrations are reached in 1.4 to 4.8 hours. Bioavailability is about 98%.

Metabolism

Primarily hepatic glucuronidation to inactive metabolites.

Valproate

Increases lamotrigine plasma concentrations by approximately two-fold, requiring a lower starting and maintenance dose of lamotrigine.

Rifampicin

May decrease lamotrigine levels.

Oral Contraceptives (containing estrogen)

May decrease lamotrigine levels. Dosage adjustment of lamotrigine may be needed.

Carbamazepine, Phenytoin, Phenobarbital, Primidone

Decreases lamotrigine plasma concentrations by approximately 40-60%, requiring a higher starting and maintenance dose of lamotrigine.