Adults

Dosage varies significantly based on indication and concomitant medications. Typically started with 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

Generally, no specific dosage adjustment is required based on age alone, but caution is advised due to potential for decreased renal/hepatic function.

Renal_impairment

Reduced maintenance doses may be necessary in patients with significant renal impairment. Initial doses should be based on concomitant medication.

Onset

Onset of action is gradual, typically requiring several weeks of titration to reach therapeutic levels, especially in bipolar disorder.

Excretion

Mainly excreted in urine (about 94%), predominantly as glucuronide conjugates. Less than 10% is excreted unchanged.

Half life

Approximately 25-33 hours in healthy adults. Can be significantly affected by concomitant medications (e.g., decreased by enzyme-inducing AEDs, increased by valproate).

Absorption

Rapid and complete absorption after oral administration, bioavailability is approximately 98%. Peak plasma concentrations are reached between 1.4 to 4.8 hours.

Metabolism

Primarily metabolized by glucuronidation (UGT1A4, UGT2B7, UGT1A1) in the liver to inactive metabolites.

Valproate

Increases lamotrigine plasma concentrations by inhibiting glucuronidation, requiring a significant reduction in lamotrigine dose.

Rifampicin

Decreases lamotrigine levels by inducing drug-metabolizing enzymes.

Lopinavir/Ritonavir

Decreases lamotrigine levels.

Oral Contraceptives (containing estrogen)

Can decrease lamotrigine levels. Dose adjustments may be necessary.

Carbamazepine, Phenytoin, Phenobarbital, Primidone

Decrease lamotrigine plasma concentrations by inducing glucuronidation, requiring an increase in lamotrigine dose.