TEST CATALOG ORDERING & RESULTS SPECIMEN HANDLING CUSTOMER SERVICE EDUCATION & INSIGHTS
Test Catalog

Test ID: CARTF    
Carbamazepine Profile, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Monitoring patients exhibiting symptoms of carbamazepine toxicity whose total serum carbamazepine concentration is within the therapeutic range, but who may be producing significant levels of the active metabolite epoxide

 

Free carbamazepine concentration may also be useful to monitor in patients with altered or unpredictable protein binding capacity

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Carbamazepine is a common antiepileptic drug. It is a first-line drug for treatment of partial seizures and trigeminal neuralgia.

 

Carbamazepine is metabolized by the liver to carbamazepine-10,11-epoxide (CBZ10-11), which is pharmacologically active and potentially toxic. CBZ10-11 is, in turn, inactivated by hepatic conversion to a transdiol derivative.

 

CBZ10-11 may be responsible for the congenital abnormalities that are sometimes associated with the use of carbamazepine during early pregnancy. There have been cases of severe seizures exacerbation when serum epoxide levels were increased. Toxic levels of CBZ10-11 can occur during:

-Concomitant administration of other drugs that induce hepatic oxidizing enzymes (eg, most antiepileptic drugs [with the exception of valproic acid and the benzodiazepines], propoxyphene)

-Concomitant administration of drugs that inhibit its breakdown such as valproic acid, felbamate, and lamotrigine

-High-dose carbamazepine therapy, especially in combination with the above conditions

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

CARBAMAZEPINE, TOTAL

Therapeutic: 4.0-12.0 mcg/mL

Critical value: > or =15.0 mcg/mL

 

CARBAMAZEPINE-10,11-EPOXIDE

Therapeutic: 0.4-4.0 mcg/mL

Toxic concentration: > or =8.0 mcg/mL

 

CARBAMAZEPINE, FREE

Therapeutic: 1.0-3.0 mcg/mL

Critical value: > or =4.0 mcg/mL

Interpretation Provides information to assist in interpretation of the test results

The clinically acceptable serum concentration of carbamazepine-10,11-epoxide (CBZ10-11) is not well established, but 4.0 mcg/mL has often been used as an upper limit for its therapeutic range.

 

The ratio of CBZ10-11 to carbamazepine is usually less than or equal to 0.2 mcg/mL in symptomatic adults and less than or equal to 0.3 mcg/mL in children.

 

Clinical correlation is aided by comparing values obtained when the patient is symptomatic with those obtained when the patient has improved.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Routine determination of carbamazepine-10,11-epoxide (CBZ10-11) is not clinically indicated. It should be considered when the source of treatment in associated symptoms is not obvious.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Theodore WH, Narang PK, Holmes MD, et al: Carbamazepine and its epoxide: relation of plasma levels to toxicity and seizure control. Ann Neurol 1989;25:194-196

2. Tomson T, Almkvist O, Nilsson BY, et al: Carbamazepine-10, 11-epoxide in epilepsy. A pilot study. Arch Neurol 1990;47:888-892

3. McKauge L, Tyrer JH, Eadie MI: Factors influencing simultaneous concentrations of carbamazepine and its epoxide in plasma. Ther Drug Monit 1981;3:63-70

4. Brodie MJ, Forrest G, Rapeport WG: Carbamazepine-10,11-epoxide concentrations in epileptics of carbamazepine alone and in combination with other anticonvulsants. Br J Clin Pharmacol 1983;16:747-749

5. Shoeman JF, Elyas AA, Brett EM, Lascelles PT: Correlation between plasma carbamazepine-10,11-epoxide concentration and drug side-effects in children with epilepsy. Dev Med Child Neurol 1984;26:756-764