Test Catalog

Test Id : PRMB

Primidone and Phenobarbital, Serum

Useful For
Suggests clinical disorders or settings where the test may be helpful

Assessing compliance


Monitoring for appropriate therapeutic levels of primidone and phenobarbital


Assessing toxicity

Profile Information
A profile is a group of laboratory tests that are ordered and performed together under a single Mayo Test ID. Profile information lists the test performed, inclusive of the test fee, when a profile is ordered and includes reporting names and individual availability.

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

Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Includes phenobarbital determination.

Method Name
A short description of the method used to perform the test

PRIMD: Immunoassay

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

NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.


Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test

Primidone and Phenobarbital, S

Lists additional common names for a test, as an aid in searching

Barbita (Phenobarbital)

Luminal (Phenobarbital)

Mysoline (Primidone)


Primidone (Mysoline)

Primidone w/Phenobarb Metabolite, Serum

Solfoton (Phenobarbital)

Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Includes phenobarbital determination.

Specimen Type
Describes the specimen type validated for testing


Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing


Preferred: Serum gel

Acceptable: Red top

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 aliquoted within 2 hours of collection.


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)

Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the Testing Laboratory

0.25 mL

Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected

Gross hemolysis Reject

Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included

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

Useful For
Suggests clinical disorders or settings where the test may be helpful

Assessing compliance


Monitoring for appropriate therapeutic levels of primidone and phenobarbital


Assessing toxicity

Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Includes phenobarbital determination.

Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Primidone is used for control of grand mal seizures that are refractory to other antiepileptics and seizures of psychomotor or focal origin.


Primidone is initially dosed in progressively increasing amounts starting with 100 mg at bedtime to 250 mg 3 times a day after 10 days of therapy in adults.


Primidone exhibits a volume of distribution of 0.6 L/kg and a half-life of 8 hours.


When monitoring primidone and phenobarbital levels simultaneously, the specimen should be drawn just before the next dose is administered.


Primidone is not highly protein bound, approximately 10%. Phenobarbital is a metabolite of primidone. Like phenobarbital, there are no known major drug-drug interactions that affect the pharmacology of primidone. Toxicity associated with primidone is primarily due to the accumulation of phenobarbital. Diagnosis and treatment are as described for PBAR / Phenobarbital, Serum.

Reference Values
Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


Therapeutic: 5.0-12.0 mcg/mL

Critical value: > or =15.0 mcg/mL



Therapeutic: 10.0-40.0 mcg/mL

Critical value: > or =60.0 mcg/mL

Provides information to assist in interpretation of the test results

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 <5 years of age.


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 <5 years of age.


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

Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

At the same time that the primidone level is monitored, one should also monitor the phenobarbital level, as phenobarbital is a metabolite of primidone.

Clinical Reference
Recommendations for in-depth reading of a clinical nature

Rall TW, Schleifer LS: Drugs effective in the therapy of the epilepsies: primidone. In Goodman and Gilman's The Pharmacological Basis of Therapeutics. Eighth edition. Edited by AG Gilman, TW Rall, AS Nies, P Taylor. New York, Pergamon Press, 1990, pp 446-447

Method Description
Describes how the test is performed and provides a method-specific reference


The assay is a homogeneous enzyme immunoassay technique used for the analysis of specific compounds in biological fluids. The assay is based on competition between drug in the sample and drug labeled with the enzyme glucose-6-phosphate dehydrogenase (G6PDH) for antibody binding sites. Enzyme activity decreases upon binding to the antibody, so the drug concentration in the sample can be measured in terms of enzyme activity. Active enzyme converts oxidized nicotinamide adenine dinucleotide (NAD) to NADH (the reduced form of NAD), resulting in an absorbance change that is measured spectrophotometrically. Endogenous serum G6PDH does not interfere, because the coenzyme functions only with the bacterial (leuconostoc mesenteroides) enzyme employed in the assay.(Package insert: Seimens Primidone reagent, Seimens Healthcare Diagnostics Ltd., Newark, DE)



The assay is based on the kinetic interaction of microparticles in a solution (KIMS). Phenobarbital antibody is covalently coupled to microparticles and the drug derivative is linked to a macromolecule. The kinetic interaction of microparticles in solutions is induced by binding of drug-conjugate to the antibody on the microparticles and is inhibited by the presence o fphenobarbital in the sample. A competitive reaction takes place between the drug conjugate and phenobarbital in the serum sample for binding to the phenobarbital antibody on the microparticles. The resulting kinetic interaction of microparticles is indirectly proportional to the amount of drug present in the sample.(Package insert: Roche Phenobarbital reagent, Roche Diagnostic Corp, Indianapolis, IN)

PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information


Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.

Monday through Sunday

Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.

Same day/1 day

Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

1 week

Performing Laboratory Location
Indicates the location of the laboratory that performs the test


Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.

  • Authorized users can sign in to Test Prices for detailed fee information.
  • Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
  • Prospective clients should contact their Regional Manager. For assistance, contact Customer Service.

Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.

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
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.

CPT codes are provided by the performing laboratory.



LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.

Test Id Test Order Name Order LOINC Value
PRMB Primidone and Phenobarbital, S 10547-8
Result Id Test Result Name Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
PBR Phenobarbital, S 3948-7
PRIMD Primidone, S 3978-4

Test Setup Resources

Setup Files
Test setup information contains test file definition details to support order and result interfacing between Mayo Clinic Laboratories and your Laboratory Information System.

Excel | Pdf

Sample Reports
Normal and Abnormal sample reports are provided as references for report appearance.

Normal Reports | Abnormal Reports

SI Sample Reports
International System (SI) of Unit reports are provided for a limited number of tests. These reports are intended for international account use and are only available through MayoLINK accounts that have been defined to receive them.

SI Normal Reports | SI Abnormal Reports