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Test Code PRMB Primidone and Phenobarbital, Serum

Important Note

  • Primadone (Mysoline) cannot be ordered by itself
  • It must be ordered in conjunction with Phenobarbitol as it appears in this test.

Additional Codes

Mysoline

Phenobarbitol

Useful For

Assessing compliance

 

Monitoring for appropriate therapeutic levels of primidone and phenobarbital

 

Assessing toxicity

Profile Information

Test ID Reporting Name Available Separately Always Performed
PRIMD Primidone, S No Yes
PBR Phenobarbital, S Yes Yes

Testing Algorithm

Includes phenobarbital determination.

Method Name

PRIMD: Immunoassay

PBR: Kinetic Interaction of Microparticles in a Solution (KIMS)

Reporting Name

Primidone and Phenobarbital, S

Specimen Type

Serum


Specimen Required


Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions:

1. Serum gel tubes should be centrifuged within 2 hours of collection.

2. Red-top tubes should be centrifuged, and the serum aliquoted into a plastic vial within 2 hours of collection.


Specimen Minimum Volume

0.25 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 7 days
  Frozen  28 days
  Ambient  72 hours

Reference Values

Primidone

Therapeutic: 5.0-12.0 mcg/mL

Critical value: ≥15.0 mcg/mL

 

Phenobarbital

Therapeutic: 10.0-40.0 mcg/mL

Critical value: ≥60.0 mcg/mL

Interpretation

At steady-state, which is achieved approximately 2 weeks after therapy is initiated, blood levels of primidone that correlate with optimal response to the drug range from 9.0 to 12.5 mcg/mL for adults and 7.0 to 10.0 mcg/mL for children younger than 5 years.

 

The corresponding levels for phenobarbital are 20.0 to 40.0 mcg/mL for adults and 15.0 to 30.0 mcg/mL for children younger than 5 years.

 

Dosage adjustment based on blood level information is the best way to obtain optimal response to the drug.

Clinical Reference

1. Lenkapothula N, Cascella M. Primidone. In: StatPearls [Internet]. StatPearls Publishing; 2024. Updated July 24, 2023. Available at www.ncbi.nlm.nih.gov/books/NBK562297/

2. Aronson J. Meyler's Side Effects of Drugs: The International Encyclopedia of Adverse Drug Reactions and Interactions. 16th ed. Elsevier; 2016:927-932. doi.org/10.1016/B978-0-444-53717-1.01336-6

Day(s) Performed

Monday through Sunday

Report Available

Same day/1 day

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

PRIMD-80188

PBR-80184

LOINC Code Information

Test ID Test Order Name Order LOINC Value
PRMB Primidone and Phenobarbital, S 10547-8

 

Result ID Test Result Name Result LOINC Value
PBR Phenobarbital, S 3948-7
PRIMD Primidone, S 3978-4

Forms

If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

-Neurology Specialty Testing Client Test Request (T732)

-Therapeutics Test Request (T831)