Phenobarbital Level

Abbrev Code:PHENO   
Order Code:LAB30Order Name:Phenobarbital Level
Synonyms:Also see Free Phenobarbital (FPHENO, LAB3482)
Methodology:Roche: Kinetic interaction of microparticles in a solution (KIMS)
Vista: Turbidmetric rate
Remisol:  Homogenous enzyme immunoassay
Architect: Chemiluminescent microparticle immunoassay (CMIA)
CPT Codes: 80184 x1, 80184 x1
Turnaround Time:Performed and reported 24 h/day.
Associated Links:

Roche Go Live Schedule

Collection Instructions

Optimal Volume:2.5 mL
Minimum\Peds Volume:0.8 mL
Container:Red (no gel), St Johns/Woodwinds-Green (lithium heparin, no gel)
Alternate Containers: Green (lithium heparin, no gel), Grand Itasca - Green (lithium heparin, no gel), Purple (EDTA), St Johns/Woodwinds - Red (no gel)
Collection Instructions:Trough level is preferred; collect immediately before dose. It is advisable to monitor at the same time in the dosing schedule.
Causes for Rejection:Collection in a gel tube.

Processing and Shipping

Specimen Processing:Centrifuge and aliquot 1.25 mL, 0.3 mL minimum. Store in room temperature up to 48 hours. Alternatively, refrigerate.
Shipping Instructions:Ship at room temperature to arrive within 48 hours. Alternatively, ship at refrigerated temperature.
Stability:7 days at room or refrigerated temperature; 1 year frozen.
Test Performed at or Referral Lab Chemistry  (Grand Itasca, Range, Roche-UMMC East, Southdale, UMMC West Bank)


Critical Range:Greater than 50 mg/L
Therapeutic Range:Roche: 10-30 μg/mL
Vista: 15-40 mg/L
Grand Itasca: 10-40 ug/mL

The therapeutic range of phenobarbital is correlated with seizure control as well as the absence of toxic effects, and is generally accepted to be between 10 and 30 μg/mL. Variation in metabolism and absorption of the drug may cause levels to rise above 40 μg/mL or fall below 15 μg/mL.  The most frequent dose related side effect is sedation, to which a tolerance usually develops. Phenobarbital serum levels above 40 μg/mL are often associated with nystagmus, ataxia and dysarthria. At high doses, phenobarbital can cause an increase in seizure frequency.
Use:Monitor therapeutic drug level of phenobarbital; use with primidone levels to monitor therapeutic drug level of primidone; evaluate phenobarbital toxicity. Half-life is 50-120 h (adult); and 40-70 h (child).

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