Test Catalog

Test ID: PENTS    
Pentobarbital, Serum

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

Monitoring of pentobarbital therapy treatment

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

Pentobarbital is a short-acting barbiturate with anticonvulsant and sedative-hypnotic properties. Uses include sedation induction; relief of preoperative anxiety; control of status epilepticus or seizures resulting from meningitis, tetanus, alcohol withdrawal, poisons, chorea, or eclampsia; and induction of coma in the management of cerebral ischemia and increased intracranial pressure that may follow stroke or head trauma.(1,2)


Pentobarbital is administered orally, parenterally, and rectally. The duration of hypnotic effect is about 1 to 4 hours. The drug distributes throughout the body with about 35% to 45% of a dose bound to plasma proteins in the blood. Metabolism takes place in the liver via oxidation to the inactive metabolite, hydroxypentobarbital. Elimination is biphasic; half-life is about 4 hours in the first phase, and 35 to 50 hours in the second phase. Excretion occurs through the urine, mainly as glucuronide conjugates of metabolites, with only about 1% excreted as unchanged drug.(1,2) Tolerance to the hypnotic effects of pentobarbital occurs after about 2 weeks of continuous dosing.

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

Hypnotic: 1-5 mcg/mL

Therapeutic coma: 20-50 mcg/mL

Reducing intracranial pressure: 30-40 mcg/mL

This degree of sedation requires artificial respiratory support.

Toxic concentration: >10 mcg/mL

Interpretation Provides information to assist in interpretation of the test results

Pentobarbital concentrations above 10 mcg/mL have been associated with toxicity.

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

The concentration at which toxicity occurs varies and results should be interpreted in light of 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 Recommendations for in-depth reading of a clinical nature

1. NEMBUTAL Sodium Solution (pentobarbital sodium injection). Package insert: Ovation Pharmaceuticals Inc; October 2007

2. Physician's Desk Reference (PDR): 61st edition. Thomson PDR; 2007

3. Baselt RC: Disposition of Toxic Drugs and Chemicas in Man. 10th ed. Biomedical Publications; 2014:2211

4. 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

5. 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

6. 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