Oxcarbazepine, a carboxamide, is chemically similar to carba-mazepine but causes less induction of hepatic enzymes. Oxcar-bazepine is a prodrug. It’s useful as adjunctive therapy or monotherapy for adults with partial seizures and as adjunctive therapy for children with partial seizures.
Oxcarbazepine is completely absorbed and extensively metabo-lized by hepatic enzymes to the 10-monohydroxy metabolite (MHD) that’s responsible for its pharmacologic activity. MHD is excreted primarily by the kidneys.
The half-life of MHD is about 9 hours. Unlike carbamazepine, ox-carbazepine doesn’t induce its own metabolism.
The precise mechanism of action of oxcarbazepine and its metabolite MHD is unknown, but antiseizure activity is thought to occur through blockade of sodium-sensitive channels, which pre-vents seizure spread in the brain.
Oxcarbazepine is FDA-approved as adjunctive therapy for partial seizures in adults and children older than age 4 and as monothera-py for adults.
As with carbamazepine, it’s also effective for generalized seizures but may worsen myoclonic and absence seizures.
Carbamazepine, phenytoin, phenobarbital, valproic acid, and ve-rapamil may decrease the levels of oxcarbazepine’s active metabolite MHD.
· Oxcarbazepine may decrease the effectiveness of hormonal contraceptives and felodipine.
· Dosage reductions are necessary for patients with renal impairment (creatinine clearance less than 30 ml/minute) and those at risk for renal impairment, such as elderly patients. (See Adverse reactions to oxcar-bazepine.)