Carbamazepine

Diagnostic Use

Carbamazepine is a commonly prescribed anti-epileptic drug. Rarer indications for carbamazepine therapy include trigeminal neuralgia and mood disorders.

Under normal physiological circumstances, 75-80% of the measured circulating carbamazepine is bound to plasma proteins. A free carbamazepine assay is also available and may provide useful additional information in those with an abnormal plasma protein concentration, or in those taking additional protein-bound drugs.

Department

Core Biochemistry

Delphic Registration Code

CARB

Synonyms

Tegretol
Teril

For a full list of brand names for this drug used in NZ, please see the relevant entry in the NZ Formulary

Turnaround Time

3 hours

Test Code

4648

Specimen Type

• Serum
• Plasma

Specimen Requirements

Tube/Container Type:

Preferred

• Lithium Heparin - Non-gel (Green Cap)

Acceptable

• Serum (Red Cap)
• SST II (Gold Cap)
• Lithium Heparin - Gel (Green Cap)

Preferred Sample Volume (ml)

4.5

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• Lithium Heparin - Non-gel (Green Cap)

Preferred Sample Volume (ml)

0.6

Additional Specimen Information

A trough sample should be collected (i.e. taken immediately before the next dose is due).

Drug levels should not be taken until steady state pharmacokinetics have been achieved (i.e. at least 4-5 half-lives after starting the drug/changing dose - the half-life of carbamazepine is approximately 15 hours).

Aliquot Instructions

Sample Type

• Serum
• Plasma

Minimum Volume (ml)

0.15

Transport to Lab

Chilled (2 - 8 degrees Celsius)
If overnight - Chilled (2 - 8 degrees Celsius)

Interpretation

The standard half-life of carbamazepine is 15 hours, with time to steady-state of 3 days.

Refer to the CDHB Therapeutic Drug Monitoring Profiles for advice on how to interpret carbamazepine levels.

Reference Intervals

Test	Therapeutic range
Carbamazepine	16-50μmol/L
Free carbamazepine	4-10μmol/L

 

The above ranges are a guide only.  The target plasma concentration should be tailored to the individual patient in accordance with clinical features of efficacy and/or drug toxicity.  Consultation with the clinical pharmacology team is recommended if expert advice is required.

 

 

Test Method

Performed on Beckman Coulter AU5822 analyser using Beckman Coulter reagents.

Non-Funded Test Cost

$21.42 (Exclusive of GST)

Billing Code

4648

Grossly haemolysed specimens are unsuitable for analysis.

Contact Information

Enquiry Form