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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
Collection Container/Tube: Red top (Serum gel/SST are not acceptable)
Submission Container/Tube: Plastic vial
Specimen Volume: 1.2 mL
Collection Instructions:
1. Draw blood immediately before next scheduled dose.
2. Centrifuge and aliquot serum in plastic vial within 2 hours of collection.
Specimen Minimum Volume
0.7 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| 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
Wedneday
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 US Food and Drug Administration.CPT Code Information
80345
G0480 (if appropriate)
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| MEPHS | Mephobarbital and Phenobarbital, S | 97183-8 |
| 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 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. Baselt RC: Disposition of Toxic Drugs and Chemicals in Man. 10th ed. Biomedical Publications; 2014:2211
2. Milone MC, Shaw LM: Therapeutic drugs and their management. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018:800-831
3. Langman LJ, Bechtel LK, Meier BM, Holstege C: Clinical toxicology. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier: 2018:832-887
4. Mihic SJ, Mayfield J, Harris RA: Hypnotics and sedatives. In: Brunton LL, Hilal-Dandan R, Knollmann BC, eds. Goodman and Gilman's The Pharmacological Basis of Therapeutics. 13th ed. McGraw-Hill Education; 2017
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 |
Method Name
Gas Chromatography-Mass Spectrometry (GC-MS)
Forms
If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.