Synonym

Phenobarbitone

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: 43 - 129 µmol/L

Levels above 172 are often associated with nystagmus, ataxia and dysarthria.

(Source: from manufacturer's kit insert)

Clinical indication

Therapeutic drug monitoring of phenobarbital or primidone

Result interpretation

Phenobarbital has a long half-life and a steady state may not be reached for several weeks.

Mean half-life is 100 Hr (range 50 - 150 Hr).

Primidone is metabolised to phenobarbital.

Measurement of uncertainty

See table.

Frequency of measurement

Daily