Carbamazepine - Pharmacokinetics

Pharmacokinetics

Carbamazepine exhibits autoinduction: it induces the expression of the hepatic microsomal enzyme system CYP3A4, which metabolizes carbamazepine itself. Upon initiation of carbamazepine therapy, concentrations are predictable and follow their respective baseline clearance/half-life values that have been established for the specific patient. However, after enough carbamazepine has been presented to the liver tissue, the CYP3A4 activity increases, speeding up drug clearance and shortening the half-life. Autoinduction will continue with subsequent increases in dose but will usually reach a plateau within 5–7 days of a maintenance dose. Increases in dose at a rate of 200 mg every 1–2 weeks may be required to achieve a stable seizure threshold. Stable carbamazepine concentrations occur usually within 2–3 weeks after initiation of therapy.