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HelpTest ID MEPHS Mephobarbital and Phenobarbital, Serum
Reporting Name
Mephobarbital and Phenobarbital, SUseful 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 |
Specimen Type
Serum RedSpecimen Required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube: Red top (Serum gel/SST are not acceptable)
Submission Container/Tube: Plastic vial
Specimen Volume: 2.0 mL
Collection Instructions:
1. Collect specimen immediately before next scheduled dose.
2. Centrifuge and aliquot serum into plastic vial within 2 hours of collection.
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
MEPHOBARBITAL
Therapeutic range: 1.0-7.0 mcg/mL
Toxic concentration: ≥15.0 mcg/mL
PHENOBARBITAL
Therapeutic range
Children: 15.0-30.0 mcg/mL
Adults: 20.0-40.0 mcg/mL
Toxic concentration: ≥60.0 mcg/mL
Day(s) Performed
Thursday
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
80184
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 the mephobarbital activity can be attributed to the accumulation of phenobarbital. Consequently, the pharmacological properties, toxicity, and clinical uses of mephobarbital are the same as phenobarbital.(1,2) The use of mephobarbital is uncommon as it offers no significant advantage over phenobarbital alone.(1,2)
Interpretation
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 mcg/mL have been associated with coma without reflexes.
Cautions
Concentration at which toxicity occurs varies and results should be interpreted in light of the clinical situation.
Specimens collected in serum gel tubes are not acceptable because the drug can absorb on the gel and lead to falsely decreased concentrations.
Clinical Reference
1. Langman LJ, Bechtel LK, Holstege CP. Clinical toxicology. In: Rifai N, Chiu RWK, Young I, Burnham C-AD, Wittwer CT, eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier; 2023:454-454.e484
2. Baselt RC. Disposition of Toxic Drugs and Chemical in Man. 12th ed. Biomedical Publications; 2020
3. Milone MC, Shaw LM. Therapeutic drugs and their management. In: Rifai N, Chiu RWK, Young I, Burnham C-AD, Wittwer CT, eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier; 2023:420-453
4. Mihic SJ, Mayfield J. Hypnotics and sedatives. In: Brunton LL, Knollman BC, eds. Goodman and Gilman's: The Pharmacological Basis of Therapeutics. 14th ed. McGraw-Hill Education; 2023
Method Description
Barbiturates are extracted from serum using solid-phase extraction techniques. The serum is buffered and eluted with organic solvent. The organic phase is dried, reconstituted, and analysis performed by gas chromatography-mass spectrometry, using selected ion monitoring. The assay utilizes deuterated barbiturates as internal standards.(Unpublished Mayo method)
Report Available
3 to 9 daysReject Due To
| Gross hemolysis | Reject |
| Gross lipemia | OK |
| Gross icterus | OK |
NY State Approved
YesMethod Name
Gas Chromatography Mass Spectrometry (GC-MS)
Forms
If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:
-Therapeutics Test Request (T831)