Carbamazepine, Serum or Plasma

Serum or plasma

1 mL

0.3 mL

Red-top tube or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.

This heterocyclic (iminostilbene) compound has potent antiepileptic properties and is effective alone or with other antiepileptic drugs in partial seizures, especially complex partial seizures, generalized tonic-clonic seizures, and combinations of these seizure types. Carbamazepine generally is ineffective for absence, myoclonic, and atonic seizures. In children with symptomatic generalized epilepsy and continuous spike-and-wave discharge, these seizure types may develop or tonic-clonic seizures may increase in frequency with use of carbamazepine. It has also been noted¹ that the dose of carbamazepine cannot be used as a reliable index for predicting the serum concentration of either total or free carbamazepine serum concentrations in children with epilepsy.

Comparative clinical trial data indicate that patients with partial seizures may tolerate carbamazepine better than phenobarbital and primidone, but individual responses vary. Many clinicians consider carbamazepine a drug of choice for initial therapy in idiopathic and symptomatic localization-related epilepsies, especially in children and women. This drug is increasingly preferred to phenobarbital in pediatric patients because it has less effect on cognition and behavior. It is reported to have psychotropic activity that may increase alertness and elevate mood in depressed epileptic patients, but not in otherwise normal patients. Mental improvements may be due to substitution of carbamazepine for sedative drugs, control of seizures, or a direct psychotropic effect. Carbamazepine can induce the hepatic enzymes CYP3A4, CYP1A2, and CYP2C9, resulting in decreased serum levels of many drugs (eg, alprazolam, clozapine, diazepam, haloperidol, risperidone, and tricyclic antidepressants).²

Immunoassay

Therapeutic: In conjunction with other antiepileptic drugs: 4.0−8.0 μg/mL; carbamazepine alone: 6.0−12.0 μg/mL

Leukopenia may be dose related, and necessitates stopping the drug if the absolute neutrophil count falls to <1000/mm³.³ Hyponatremia may occur, especially in older patients. Patients in the first month of pregnancy are at increased risk of neural tube defects. Carbamazepine may interfere with the actions of theophylline, oral contraceptives, oral anticoagulants, or doxycycline. Conversely, there have been reports indicating fluoxetine may mediate an increase in carbamazepine plasma concentrations due to inhibition of CYP3A4.²