Carbamazepine Epoxide & Total Drug Level

Label Mnemonic:	CBZ-EP
Epic code:	LAB21
Downtime form:	A-1a Doctor/Provider Orders - Pathology Core and Specialty Care Nursery

Commercial Mailout Laboratory
6240-8 RCP
356-8593

Specimen(s):

Serum

Specimen Instructions:

Timing of specimen collection: Pre-dose (trough) draw - At steady state concentration.

Separate serum from cells within two hours of collection.

Collection Medium:

Red top tube 5 mL (Clot Activator)

Minimum:

Preferred Minimum: 1.0 mL serum

Rejection Criteria:

Whole blood. Gel separator tubes, light blue (citrate), or yellow (SPS or ACD solution).

Testing Schedule:

Testing performed on Mondays

Turn Around Time:

1-8 days upon receipt at reference laboratory

Reference Range:

Components                     Therapeutic Range
Carbamazepine-10, 11 Epoxide   Not well established
                               Toxic: Greater than 15.0 μg/mL

Total Carbamazepine            4.0-12.0 μg/mL
                               Toxic: Greater than 15.0 
μg/mL

Interpretive Data:

The therapeutic range is based on serum pre-dose (trough) draw at steady-state concentration. The carbamazepine metabolite, Carbamazepine-10, 11-Epoxide, has anticonvulsant activity and a proposed therapeutic range of 0.4-4 μg/mL.

A rare, adverse drug reaction to carbamazepine therapy includes Stevens-Johnson syndrome or toxic epidermal necrolysis. Patients of Asian ancestry with the presence of the HLA-B*15:02 have an increased risk for this carbamazepine-induced, life-threatening reaction. Pharmacogenetic testing for HLAB* 15:02 is recommended prior to treatment for patients at risk of carbamazepine hypersensitivity. This information has been included in the FDA-approved label for carbamazepine (https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm? event=overview.process&varApplNo=016608) and in the guideline from the Clinical Pharmacogenetics Implementation Consortium (https://www.pharmgkb.org/guidelines).

A combination of therapeutic drug monitoring with HLA-B*15:02 pharmacogenetics genotyping may benefit patients at increased risk of developing carbamazepine-induced adverse events due to rare genotypes other than the HLA-B*15:02 variant allele.

Methodology:

Quantitative Liquid Chromatography-Tandem Mass Spectrometry

CPT Code:

Carbamazepine, Total, 80156; Carbamazepine, Epoxide, 80161