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HelpTest ID: CARBG Carbamazepine-10,11-Epoxide, Serum
Useful For
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, which can accumulate to concentrations equivalent to carbamazepine
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| CARTA | Carbamazepine, Tot, S | Yes | Yes |
| 1011E | Carb-10,11-Epoxide, S | No | Yes |
Method Name
CARTA: Homogeneous Microparticle Agglutination Immunoassay
1011E: High-Performance Liquid Chromatography (HPLC)
Reporting Name
Carbamazepine-10,11-Epoxide, SSpecimen Type
Serum RedSpecimen Required
Collection Container/Tube: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 2 mL
Collection Instructions:
1. Draw blood 12 hours (trough value) after last dose.
2. Centrifuge and aliquot serum into a plastic vial.
Specimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum Red | Refrigerated (preferred) | 7 days | |
| Frozen | 28 days | ||
| Ambient | 48 hours |
Clinical Information
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
CARBAMAZEPINE, TOTAL
Therapeutic: 4.0-12.0 mcg/mL
Critical value: ≥15.0 mcg/mL
CARBAMAZEPINE-10,11-EPOXIDE
Therapeutic concentration: 0.4-4.0 mcg/mL
Toxic concentration: ≥8.0 mcg/mL
Interpretation
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 ≤0.2 mcg/mL in symptomatic adults and ≤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.
Clinical Reference
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
Day(s) Performed
CARTA: Monday through Sunday
1011E: Tuesday
Report Available
Same day/1 to 7 daysTest Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
80156-Carbamazepine, Tot, S
80161-Carbamazepine-10,11-EpoxideÂ
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| CARBG | Carbamazepine-10,11-Epoxide, S | 50337-5 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 7467 | Carb-10,11-Epoxide, S | 9415-1 |
| CARTA | Carbamazepine, Tot, S | 3432-2 |
Forms
If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.
| mml-anticonvulsants |