Adults

Dosage must be slowly titrated over several weeks due to rash risk. Initial dose typically 25 mg once daily for two weeks, then 50 mg once daily for two weeks, then increased by 50-100 mg every 1-2 weeks up to a usual maintenance dose of 100-400 mg/day depending on concomitant medications and indication.

Elderly

No specific dose adjustments needed for elderly patients unless significant renal or hepatic impairment is present.

Renal_impairment

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

Onset

Clinical onset is gradual, requiring slow titration over several weeks to minimize rash risk.

Excretion

Mainly renal excretion (approximately 94%), predominantly as glucuronide conjugates.

Half life

Approximately 24-35 hours (when used alone), but can be significantly altered by co-administered drugs (e.g., decreased by enzyme inducers like carbamazepine to 13-15 hours, increased by valproate to 59-70 hours).

Absorption

Rapid and complete oral absorption, bioavailability is 98%. Peak plasma concentrations occur 1-3 hours after administration.

Metabolism

Primarily hepatic glucuronidation to inactive metabolites. Minimal cytochrome P450 metabolism.

Rifampin

Decreases lamotrigine plasma concentrations.

Valproate

Increases lamotrigine plasma concentrations by inhibiting its metabolism, necessitating a significant reduction in lamotrigine starting and maintenance doses.

Carbamazepine, Phenytoin, Phenobarbital, Primidone

Decrease lamotrigine plasma concentrations by inducing its metabolism, requiring higher lamotrigine doses.

Oral Contraceptives (containing ethinyl estradiol and levonorgestrel)

Can decrease lamotrigine plasma concentrations, potentially leading to loss of seizure control. Increased lamotrigine doses may be needed.