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Test ID MEPHS Mephobarbital and Phenobarbital, Serum

Reporting Name

Mephobarbital and Phenobarbital, S

Useful For

Monitoring of mephobarbital and phenobarbital therapy

Profile Information

Test ID Reporting Name Available Separately Always Performed
MBARS Mephobarbital, S No Yes
PHBRS Phenobarbital, S No Yes

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Serum Red

Specimen Required

Container/Tube: Red top

Specimen Volume: 2 mL

Collection Instructions: Spin down within 2 hours of draw.

Specimen Minimum Volume

0.7 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Red Refrigerated (preferred) 14 days
  Ambient  14 days
  Frozen  14 days

Reference Values


Therapeutic range: 1.0-7.0 mcg/mL

Toxic concentration: ≥15.0 mcg/mL



Therapeutic range

Children: 15.0-30.0 mcg/mL

Adults: 20.0-40.0 mcg/mL

Toxic concentration: ≥60.0 mcg/mL

Day(s) and Time(s) Performed


Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


G0480 (if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
MEPHS Mephobarbital and Phenobarbital, S In Process


Result ID Test Result Name Result LOINC Value
89706 Mephobarbital, S 3750-7
84582 Phenobarbital, S 3948-7

Clinical Information

Mephobarbital is an orally administered, methylated barbiturate used for the treatment of epilepsy.(1,2) It is demethylated by hepatic microsomal enzymes to generate its major metabolite, phenobarbital. During long-term use, most of mephobarbital's activity can be attributed to the accumulation of phenobarbital. Consequently, mephobarbital's pharmacological properties, toxicity, and clinical uses are the same as phenobarbital's.(1,2) The use of mephobarbital is uncommon as it offers no significant advantage over phenobarbital alone.(1,2)


Mephobarbital concentrations above 15 mcg/mL have been associated with toxicity.


Phenobarbital concentrations between 35 and 80 mcg/mL have been associated with slowness, ataxia, and nystagmus, while concentrations above 100 have been associated with coma without reflexes.


Concentration at which toxicity occurs varies and results should be interpreted in light of the clinical situation.

Clinical Reference

1. Teitz Textbook of Clinical Chemistry and Molecular Diagnostics. Fourth edition. Edited by CA Burtis, ER Ashwood, DE Bruns. St. Louis, MO, Elsvier Saunders, 2006, pp 1091

2. Disposition of Toxic Drugs and Chemicals in Man. Seventh edition. Edited by RC Baselt. Foster City, CA, Biomedical Publications, 2004, pp 1254

Analytic Time

1 day

Reject Due To


Mild OK; Gross reject


Mild OK; Gross OK


Mild OK; Gross OK


Serum gel tube

NY State Approved


Method Name

Gas Chromatography-Mass Spectrometry (GC-MS)