Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

FCAR
81770
CAR
8654
Carbamazepine, Free and Total, Serum
Clinical Information: Carbamazepine (Tegretol) is an effective treatment for complex partial
seizures, with or without generalization to tonic-clonic seizures. It is frequently administered in
conjunction with other antiepileptic agents, such as phenytoin and valproic acid. Under normal
circumstances, the carbamazepine that circulates in blood is 75% protein bound. In severe uremia,
carbamazepine may be displaced from protein, resulting in a higher free (unbound) fraction of the drug
circulating in blood. Since neurologic activity and toxicity are directly related to the circulating free
fraction of drug, adjustment of dosage based on knowledge of the free carbamazepine level may be useful
in patients with severe uremia.
Useful For: Monitoring carbamazepine therapy in uremic patients
Interpretation: In patients with normal renal function, optimal response is often associated with free
(unbound) carbamazepine levels >1.0 mcg/mL, and toxicity may occur when the free carbamazepine is >
or =4.0 mcg/mL. In uremic patients, the free carbamazepine level may be a more useful guide for dosage
adjustments than the total level. In patients with severe uremia, subtherapeutic total carbamazepine levels
in the range of 1.0 to 2.0 mcg/mL may be associated with therapeutic free levels. Toxicity may occur in
these patients when the free carbamazepine level is > or =4.0 mcg/mL (even though the total
carbamazepine concentration is