Specimen requirement

Adult patient:

 Heparin gel tube

Minimum blood volume: 5 mL

Paediatric patient:

Paediatric heparin tube

Number of vials: 1

Minimum blood volume: 1.3 mL

Authorisation code required

No

24 Hr available service

Yes

(Call extension: 3353 for express result)

Method

Immunoassay

Reference interval

Therapeutic: 17 - 51 µmol/L

(Source: from manufacturer's kit insert)

Clinical indication

Therapeutic drug monitoring

Result interpretation

Levels are related to the dose and the time since the previous dose.

Mean half-life is 35 Hr (range 18 - 65 Hr) early in treatment, often becoming shorter (12 - 24 Hr) with prolonged treatment due to enzyme induction by the drug (autoinduction).

For the purpose of monitoring blood levels, consistency of sample collection timing after administration of the last drug dose improves the safety and efficacy of the anticonvulsant.

Other pharmacokinetic factors such as mode of administration, dosage form, concomitant drug therapy, and biological variations in drug absorption should be taken into consideration.

Measurement of uncertainty

See table.

Frequency of measurement

Daily