Phenobarbital

Clinical Chemistry

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Description

Phenobarbital is used to control seizures. It is also the active metabolite of primidone (another anticonvulsant), and phenobarbital should usually be measured if primidone therapy monitoring is required. Where dose changes are being considered, the patient should ideally be at steady-state (a minimum of 29 days after initiation of therapy or last dose change) prior to sample collection.

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Indications

Guidance regarding use and monitoring in pregnancy is outside the scope of this summary.

Measurement of phenobarbital may be useful in the following circumstances:
- dose optimisation
- uncontrolled seizures or suspected toxicity
- in patient populations with greater metabolic variability/polypharmacy (children, pregnancy, elderly, severe intercurrent illness especially renal or hepatic impairment)
- where the formulation of the drug is altered
- where there is the possibility of drug interactions
- brain stem death testing

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Sample Type

Serum, SST/Gel, minimum 2 mL (1 mL separated serum), ideally pre-dose.

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Reference Range

Reference ranges are provided on the report. Alternatively, please contact the laboratory for current ranges.

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Turnaround Time

Within 1 day

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Testing Frequency

Daily

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External Notes

Ideally sample pre-dose for therapeutic drug monitoring (TDM) purposes. In cases of suspected toxicity, please indicate time of last dose and sample collection.

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Patient Preparation

For TDM purposes, take samples pre-dose (ideally). Patients should have attained steady-state (see below) prior to sample collection.

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Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.