Clinical and Interpretive

This assay is useful for monitoring therapy, determining compliance, and assessing toxicity.

Carbamazepine is used in the control of partial seizures with both temporal lobe and psychomotor symptoms, and for generalized tonic-clonic seizures. It is also used for analgesia in trigeminal neuralgia.

Carbamazepine exhibits a volume of distribution of 1.4 L/kg with an elimination half-life of 15 hours. Protein binding averages 75%.

Carbamazepine-10,11-epoxide (CBZ10-11) is an active metabolite that represents the predominant form of the drug in children. The volume of distribution of CBZ10-11 is 1.1 L/kg, and the half-life is 8 hours.

Aplastic anemia and agranulocytosis are rare side effects of treatment with carbamazepine; baseline hematologic data should be documented before treatment is initiated.

Toxicity associated with carbamazepine overdose occurs when the blood level is ≥15.0 mcg/mL and is typified by irregular breathing, muscle irritability, and hyperreflexia; followed by hyporeflexia, tachycardia, hypotension, and impaired consciousness with coma in severe toxicity; the higher the blood level, the more severe the symptoms.

Dosage adjustments are usually guided by monitoring blood levels. Most patients respond well when the serum concentration is in the range of 4.0 to 12.0 mcg/mL. Toxicity often occurs when levels are ≥15.0 mcg/mL. Optimal response occurs when the CBZ10-11 level is in the range of 0.4 to 4.0 mcg/mL.