amobarbital (Rx)

1-10%

Somnolence

<1%

Nervous system: agitation, confusion, hyperkinesia, ataxia, CNS depression, nightmares, nervousness, psychiatric disturbance, hallucinations, insomnia, anxiety, dizziness, abnormality in thinking

Cardiovascular system: Bradycardia, hypotension, syncope

Respiratory system: apnea, hypoventilation, postoperative atelectasis

Digestive system: Constipation, vomiting, nausea

Other adverse effects: Headache, injection site reactions, hypersensitivity reactions, fever, liver damage, megaloblastic anemia following chronic phenobarbital use

Contraindications

Hypersensitivity

Patients with history of manifest or latent porphyria

Significant impairment of liver function

Respiratory disease in which dyspnea or obstruction is evident

Cautions

Habit forming; tolerance and psychological dependence may occur with continued use

Caution in patients that are mentally depressed, have suicide ideation or history of drug abuse and hepatic damage

Rapid administration may cause respiratory depression, apnea, laryngospasm, or vasodilatation with decrease in blood pressure

Parenteral solutions of barbiturates are highly alkaline; care should be taken to avoid perivascular extravasation or intra-arterial injection

Amobarbital may diminish systemic effects of exogenous and endogenous corticosteroids. Administer with caution to patients with borderline hypoadrenal function, regardless of whether it is of pituitary or of primary adrenal origin

Possible impairment of mental and/or physical abilities required for the performance of potentially hazardous tasks, such as driving a car or operating machinery

Concurrent use of barbiturates with other CNS depressants (eg, alcohol, narcotics, tranquilizers, antihistamines) may result in increased CNS-depressant effects

Extravascular injection may cause local tissue damage with subsequent necrosis; consequences of intra-arterial injection may vary from transient pain to gangrene of the limb; any complaint of pain in the limb warrants stopping the injection

Pregnancy Category: D

Lactation: small amounts of barbiturates are excreted in the milk; use caution

Pregnancy Categories

A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

NA: Information not available.

Mechanism of Action

Depress the sensory cortex by interfering with transmission of impulses from thalamus. This results in decreased motor activity, altered cerebellar function, drowsiness, sedation, and hypnosis

Absorption

Onset: Within 5 minutes

Metabolism

Primarily hepatic via microsomal enzymes

Elimination

Half-life: 15-40 hours in adults (mean 25 hours)

Excretion: Feces, urine

IV Administration

Slow IV injection is essential; observe patients carefully during administration

Blood pressure, respiration, and cardiac function must be maintained, vital signs be recorded and equipment for resuscitation and artificial ventilation be available

The rate of IV injection for adults should not exceed 50 mg/min to prevent sleep or sudden respiratory depression

Final dosage is determined largely by the patient’s reaction to the slow administration of the drug

IM Administration

IM injection of the sodium salts of barbiturates should be made deeply into a large muscle

Average IM dose ranges from 65 mg-500 mg; volume of 5 mL (irrespective of concentration) should not be exceeded at any one site because of possible tissue irritation

Twenty percent solutions may be used so that a small volume can contain a large dose; monitor vital signs after IM injection of hypnotic dose

Superficial IM or subcutaneous injections may be painful and may produce sterile abscesses or sloughs