Absorption Peak plasma levels are reached approximately 4-5 hours after an oral dose. Nearly the entire administered dose is absorbed. Food appears to have almost no effect on the absorption of Trileptal in either tablet or suspension form.

Distribution and metabolism
Trileptal is chemically and structurally similar to carbamazepine, but undergoes a different metabolic process. Carbamazepine is oxidized to the 10,11 epoxide and then hydrolyzed. Trileptal undergoes reduction of the carbonyl group to form MHD by a cytosolic, non-microsomal, non-inducible keto-reductase. MHD is the active metabolite of Trileptal and accounts for its antiseizure activity. The half-life of MHD averages 8 to 10 hours and is stable during chronic Trileptal therapy in co-medicated patients. MHD is approximately 40% protein-bound.

Because unchanged Trileptal and its metabolites are nearly entirely excreted in the urine, hepatic impairment has no apparent affect on the pharmacokinetics of Trileptal or MHD. However, because Trileptal metabolites are cleared renally, MHD levels are significantly increased in patients with reduced creatinine clearances. Trileptal dosages in patients with renal impairment should be reduced by 50% and the titration phase should be prolonged.

Steady state
Steady state is achieved after 3 to 4 Trileptal doses in a twice-daily regimen. The dose that a patient takes should not be increased until steady state has been reached (or some time later), so that the effects of the previous dosage can be assessed.