Adults

Initial dose is typically 25 mg once daily for two weeks, followed by 50 mg once daily for two weeks. Further increments of 50-100 mg every 1-2 weeks depending on concomitant medications and clinical response. Maintenance dose usually 100-400 mg/day in 1-2 divided doses. 5 mg tablets are primarily for initial slow titration in very sensitive patients or specific pediatric protocols.

Elderly

Similar to adults, but careful monitoring and slower titration may be required due to potential age-related physiological changes and organ impairment.

Renal_impairment

Reduced maintenance doses may be required, especially in severe impairment. Initial dose and titration should be carefully adjusted based on the degree of impairment and dialysis status. Consult specific guidelines.

Onset

Onset of action for seizure control is typically gradual, requiring titration over several weeks to achieve therapeutic levels.

Excretion

Excreted mainly in the urine as glucuronide conjugates (approximately 90%) and as unchanged drug (about 10%).

Half life

Approximately 25-30 hours (can be affected by co-administered drugs; e.g., valproate prolongs, enzyme inducers shorten).

Absorption

Rapid and complete absorption after oral administration, bioavailability is approximately 98%. Peak plasma concentrations occur 1-4 hours post-dose.

Metabolism

Primarily metabolized in the liver by glucuronidation, mainly by UGT1A4 enzyme.

Valproate

Increases lamotrigine levels significantly (by inhibiting glucuronidation); requires substantial reduction in lamotrigine dose.

Rifampicin

Decreases lamotrigine levels; may require dose adjustment.

Lopinavir/Ritonavir, Atazanavir/Ritonavir

Can decrease lamotrigine levels.

Oral Contraceptives (estrogen-containing)

Can decrease lamotrigine levels, leading to loss of seizure control or mood instability; may require dose adjustment.

Carbamazepine, Phenytoin, Phenobarbital, Primidone

Decreases lamotrigine levels (by inducing glucuronidation); requires an increase in lamotrigine dose.