Adults

Initial dose typically 25 mg once daily for two weeks, then 50 mg once daily for two weeks. Dosage is then gradually increased to a maintenance dose, usually 100-400 mg/day, depending on concomitant medications.

Elderly

Similar to adults, but dosage adjustments may be necessary based on renal or hepatic function and careful monitoring.

Renal_impairment

Reduced maintenance doses may be required in patients with significant renal impairment. Use with caution and monitor closely.

Onset

Therapeutic effects typically develop over several weeks due to the need for slow titration to minimize rash risk.

Excretion

Excreted predominantly in the urine as glucuronide conjugates (about 90% of the dose).

Half life

Approximately 25-30 hours with monotherapy; significantly reduced (e.g., 15 hours) with enzyme-inducing anticonvulsants and prolonged (e.g., 59 hours) with valproate.

Absorption

Rapid and complete oral absorption, with absolute bioavailability of about 98%. Peak plasma concentrations are reached 1-3 hours post-dose.

Metabolism

Primarily hepatic glucuronidation, forming inactive metabolites.

Valproate

Increases lamotrigine plasma concentrations by inhibiting its metabolism, requiring a reduced lamotrigine dose.

Rifampicin

Decreases lamotrigine plasma concentrations.

Oral Contraceptives (estrogen-containing)

May decrease lamotrigine plasma concentrations, requiring dose adjustments.

Carbamazepine, Phenytoin, Phenobarbital, Primidone

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