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Test ID: PENTS Pentobarbital, Serum

Reporting Name

Pentobarbital, S

Useful For

Monitoring of pentobarbital therapy treatment

Clinical Information

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 pentobarbital's hypnotic effects occurs after about 2 weeks of continuous dosing.


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

Analytic Time

1 day

Day(s) and Time(s) Performed

Wednesday; 12 a.m.

Clinical Reference

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

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

3. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Fourth edition. St. Louis, MO. Elsevier Saunders, 2006, p 2312

4. Nader R, Horwath AR, Wittwer CT: In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Sixth edition. St. Louis, MO, Elsevier, 2018

Method Name

Gas Chromatography-Mass Spectrometry (GC-MS)

Specimen Type

Serum Red

Specimen Required

Collection Container/Tube: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1.2 mL

Collection Instructions:

1. Draw blood immediately before next scheduled dose.

2. Within 2 hours of collection, the specimen must be centrifuged and the serum aliquoted into a plastic vial.

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

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

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
PENTS Pentobarbital, S 3924-8


Result ID Test Result Name Result LOINC Value
8239 Pentobarbital, S 3924-8


If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-Epilepsy, mml-Neuro-oncology