MEPHS - Clinical: Mephobarbital and Phenobarbital, Serum

Test Catalog

Test Name

Test ID: MEPHS    
Mephobarbital and Phenobarbital, Serum

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

Monitoring of mephobarbital and phenobarbital therapy

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

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)

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 range: 1.0-7.0 mcg/mL

Toxic concentration: > or =15.0 mcg/mL



Therapeutic range

Children: 15.0-30.0 mcg/mL

Adults: 20.0-40.0 mcg/mL

Toxic concentration: > or =60.0 mcg/mL

Interpretation Provides information to assist in interpretation of the test results

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.

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

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

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

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