Pentobarbital
 NAME OF DRUG: Pentobarbital (Pentobarbitone, Nembutal) |
| PHYSICAL CHARACTERISTICS: Pentobarbital is available as either the free acid or sodium salt. The free acid is a fine white crystalline powder that is only slightly soluble in water and ethanol. The salt is a white crystalline powder or granules and is very soluble in water and ethanol. |
| DOSAGE/OCCURRENCE/USAGE: Pentobarbital is a popular short-acting barbiturate derivative used primarily as a sedative. It is also used to reduce intracranial pressure and lower cerebral oxygen demand in patients with severe head trauma, Reye’s syndrome, or anoxic brain damage. It is available alone or with other drugs in 15-200 mg amounts for oral, intramuscular, or rectal administration. |
| BLOOD CONCENTRATIONS VS. DOSAGE: Peak serum concentrations of 1200-3100 ng/mL were reached at 0.5-2.0 hours after the administration of a single 100 mg oral dose. The concentration levels declined to an average of 300 ng/mL after 48 hours. In one study, five subjects were given a 600 mg oral dose. Over a 3 hour period an average blood concentration of 3000 ng/mL (range 1800-4700) was observed after 0.5 hours. The levels stayed constant for 4.5 hours then diminishing to 1500 ng/mL (range 1200-1700) after 18 hours. In a study on intravenous use, the average plasma concentration in five subjects 5 minutes after a 50 mg intravenous dose was 1180 ng/mL range 1050-1330). Levels declined to 540 ng/mL by one hour and 270 ng/mL by 24 hours. |
| URINE EXCRETION RATE: Up to 86% of a dose of pentobarbital is excreted in the urine in 6 days. Approximately 1% is the unchanged drug, 73% is the diasterisomers of 3'-hydroxypentobarbital, and 15% is N-hydroxypentobarbital. In one study after a 600 mg oral dose of pentobarbital, urine concentrations ranged from 700-1800 ng/mL throughout a 21 hour period. |
| METABOLITES: 3'-hydroxypentobarbital and N-hydroxypentobarbital. |
| TOXICITY: The lethal dose level of pentobarbital is 2-10 g. This produces blood concentrations ranging from 5000-112000 ng/mL (average 35000). |
| REFERENCES: Baselt, R C. Disposition of Toxic Drugs and
Chemicals in Man, Second Edition. Davis, Calif.: Biomedical Publications, 1982. Clarke, E.G.C. Isolation and Identification of Drugs. London: The Pharmaceutical Press, 1969. Shaw, Richard F., Finkle, Bryan S. Barbiturates Abused Drugs Monograph Series. Ed. Caplan, Yale H. Irving: Abbott Laboratories, 1994. |