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Paediatric Laboratory Medicine

Phenobarbital

Clinical Significance

Phenobarbital is the most effective barbiturate in long-term treatment of seizure disorders. Strong correlation has been observed between serum levels and both therapeutic and toxic effects. Phenobarbital is excreted, partly metabolized and partly unchanged, very slowly through the urine. Both metabolism and clearance are highly variable among individuals; therefore, close monitoring of serum levels is essential for every patient undergoing Phenobarbital therapy. Clinical observations indicate that toxicity of phenobarbital is increased in patients with renal disease. Phenobarbital toxicity primarily affects the central nervous system. Some patients on long term therapy may develop macrocytosis, magaloblastic anemia and osteomalacia.

Test Name

Phenobarbital

Test Code

PHEB

Drug Class

Anticonvulsants

Division

Therapeutic Drug Monitoring - TDM

Method

Abbott Architect ci4100

External Proficiency Testing

CAP
QMPLS

Turn Around Time

Daily (throughout the day)

Disease/Condition

Anticonvulsant

Specimen Type

Serum, Plasma (Heparin or Citrate)

Minimum Specimen Requirements

150 uL

Optimal Collection Time

Trough: 0-30 minutes prior to dose

Storage/Transportation

4°C (transport with a cool pack if possible)

Approval is not required

CPT Codes

80184

Shipping and Contact Information

The Hospital for Sick Children
Rapid Response Laboratory
170 Elizabeth Street, Room 3642
Toronto, ON
M5G 2G3
Canada
Phone: 416-813-7200
Phone: 1-855-381-3212

Therapeutic Range

65-170 umol/L

Critical Values

>225 umol/L