Amobarbital

U.S. BRAND NAMES — Amytal®

PHARMACOLOGIC CATEGORY
Barbiturate

DOSING: ADULTS
Hypnotic: I.M., I.V.: 65-200 mg at bedtime (maximum single dose: 1000 mg)

Sedative: I.M., I.V.: 30-50 mg 2-3 times/day (maximum single dose: 1000 mg)

"Amytal® interview" (unlabeled use): I.V.: 50-100 mg/minute for total dose of 200-1000 mg or until patient experiences drowsiness, impaired attention, slurred speech, or nystagmus

Wada test (unlabeled use): Intra-arterial: 100 mg over 4-5 seconds via percutaneous transfemoral catheter

DOSING: PEDIATRIC

(For additional information see "Amobarbital: Pediatric drug information")
Sedative: I.M., I.V.: 6-12 years: Manufacturer's dosing range: 65-500 mg

Hypnotic (unlabeled use): I.M.: 2-3 mg/kg (maximum: 500 mg)

DOSING: ELDERLY — Refer to adult dosing.

DOSING: RENAL IMPAIRMENT — Dosing should be reduced; specific recommendations not available.

DOSING: HEPATIC IMPAIRMENT — Dosing should be reduced; specific recommendations not available.

DOSAGE FORMS — Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Injection, powder for reconstitution, as sodium:
Amytal®: 500 mg

DOSAGE FORMS: CONCISE
Injection, powder for reconstitution:
Amytal®: 500 mg

GENERIC EQUIVALENT AVAILABLE — No

ADMINISTRATION
I.M.: Administer deeply into a large muscle. Do not use more than 5 mL at any single site (may cause tissue damage). I.M. dosages should not exceed 500 mg. Use 20% solution to facilitate larger doses.

I.V.: Use only when I.M. administration is not feasible. Administer by slow I.V. injection (maximum: 50 mg/minute in adults).

COMPATIBILITY — Stable in D5LR, D5NS, D5W, D10W, D20W, LR, NS.

Compatibility when admixed: Compatible: Amikacin, aminophylline, sodium bicarbonate. Incompatible: Cefazolin, cimetidine, clindamycin, diphenhydramine, droperidol, hydroxyzine, insulin (regular), levorphanol, meperidine, morphine, norepinephrine, pancuronium, pentazocine, penicillin G potassium, procaine, streptomycin, vancomycin. Variable (consult detailed reference): Atracurium, dimenhydrinate, hydrocortisone sodium succinate, isoproterenol, metaraminol, methyldopate, norepinephrine, succinylcholine.

USE — Hypnotic in short-term treatment of insomnia; reduce anxiety and provide sedation preoperatively

USE - UNLABELED / INVESTIGATIONAL — Therapeutic or diagnostic "Amytal® Interviewing"; Wada test

ADVERSE REACTIONS SIGNIFICANT — Frequency not defined and is reported as barbiturate use (not specifically amobarbital).

Cardiovascular: Bradycardia, hypotension, syncope

Central nervous system: Agitation, anxiety, ataxia, confusion, CNS depression, dizziness, fever, hallucinations, headache, insomnia, nightmares, nervousness, psychiatric disturbances, somnolence, thinking abnormal

Gastrointestinal: Constipation, nausea, vomiting

Hematologic: Megaloblastic anemia (following chronic phenobarbital use)

Hepatic: Liver damage

Local: Injection site reaction

Neuromuscular & skeletal: Hyperkinesia

Respiratory: Apnea, atelectasis (postoperative), hypoventilation

Miscellaneous: Hypersensitivity reaction (including angioedema, rash, and exfoliative dermatitis)

CONTRAINDICATIONS — Hypersensitivity to barbiturates or any component of the formulation; marked hepatic impairment; dyspnea or airway obstruction; porphyria

WARNINGS / PRECAUTIONS
Concerns related to adverse effects: CNS depression: May cause CNS depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks which require mental alertness (eg, operating machinery or driving). Hypersensitivity reactions: Postmarketing studies have indicated that the use of hypnotic/sedative agents for sleep has been associated with hypersensitivity reactions including anaphylaxis as well as angioedema. Paradoxical responses: May cause paradoxical responses, including agitation and hyperactivity, particularly in acute pain, chronic pain and pediatric patients. Sleep-related activities: An increased risk for hazardous sleep-related activities such as sleep-driving; cooking and eating food, and making phone calls while asleep has been noted with sedative-hypnotic medications. Discontinue treatment in patients who report a sleep-driving episode.

Disease-related concerns: Cardiovascular disease: Use with caution in patients with cardiovascular disease; may cause hypotension. Depression: Use with caution in patients with depression or suicidal tendencies. Drug abuse: Use with caution in patients with a history of drug abuse or acute alcoholism; potential for drug dependency exists. Tolerance, psychological and physical dependence may occur with prolonged use. Hepatic impairment: Use with caution in patients with hepatic impairment, decreased dosage may be needed; contraindicated in severe impairment. Insomnia: Appropriate use: When used as a hypnotic for the treatment of insomnia, effectiveness is limited to ≤ 2 weeks. Renal impairment: Use with caution in patients with renal impairment; decreased dosage may be needed.

Concurrent drug therapy issues: Sedatives: Effects may be potentiated when used with other sedative drugs or ethanol.

Special populations: Elderly: Use with caution in the elderly; not recommended for use. Closely monitor elderly or debilitated patients for impaired cognitive or motor performance. Pediatrics: Safety and efficacy have not been established in children <6 years of age; use with caution in children ≥ 6 years of age.

Dosage form specific issues: Alkaline solution: Solution for injection is highly alkaline and extravasation may cause local tissue damage.

Other warnings/precautions: Rapid administration: Rapid I.V. administration may cause respiratory depression, apnea, and hypotension. Withdrawal: Gradual withdrawal is recommended if used over extended periods of time.

RESTRICTIONS — C-II

METABOLISM / TRANSPORT EFFECTS — Induces CYP2A6 (strong)

DRUG INTERACTIONS
Acetaminophen: Barbiturates may increase the metabolism of Acetaminophen. This may 1) diminish the effect of acetaminophen; and 2) increase the risk of liver damage. Risk C: Monitor therapy

Alcohol (Ethyl): CNS Depressants may enhance the CNS depressant effect of Alcohol (Ethyl). Risk C: Monitor therapy

Beta-Blockers: Barbiturates may decrease the serum concentration of Beta-Blockers. Exceptions: Atenolol; Levobunolol; Metipranolol; Nadolol. Risk C: Monitor therapy

Calcium Channel Blockers: Barbiturates may increase the metabolism of Calcium Channel Blockers. Exceptions: Clevidipine. Risk D: Consider therapy modification

Chloramphenicol: May decrease the metabolism of Barbiturates. Barbiturates may increase the metabolism of Chloramphenicol. Risk D: Consider therapy modification

CNS Depressants: May enhance the adverse/toxic effect of other CNS Depressants. Risk C: Monitor therapy

Contraceptive (Progestins): Barbiturates may diminish the therapeutic effect of Contraceptive (Progestins). Contraceptive failure is possible. Risk D: Consider therapy modification

Corticosteroids (Systemic): Barbiturates may increase the metabolism of Corticosteroids (Systemic). Risk C: Monitor therapy

CycloSPORINE: Barbiturates may increase the metabolism of CycloSPORINE. Risk D: Consider therapy modification

CYP2A6 Substrates: CYP2A6 Inducers (Strong) may increase the metabolism of CYP2A6 Substrates. Risk C: Monitor therapy

Disopyramide: Barbiturates may increase the metabolism of Disopyramide. Risk D: Consider therapy modification

Doxycycline: Barbiturates may decrease the serum concentration of Doxycycline. Risk D: Consider therapy modification

Etoposide: Barbiturates may increase the metabolism of Etoposide. Risk C: Monitor therapy

Etoposide Phosphate: Barbiturates may decrease the serum concentration of Etoposide Phosphate. Barbiturates may increase the metabolism, via CYP isoenzymes, of etoposide phosphate. Risk C: Monitor therapy

Felbamate: May increase the serum concentration of Barbiturates. Risk C: Monitor therapy

Griseofulvin: Barbiturates may decrease the absorption of Griseofulvin. Risk D: Consider therapy modification

LamoTRIgine: Barbiturates may increase the metabolism of LamoTRIgine. Risk D: Consider therapy modification

Meperidine: Barbiturates may enhance the CNS depressant effect of Meperidine. Risk C: Monitor therapy

Methadone: Barbiturates may increase the metabolism of Methadone. Risk D: Consider therapy modification

Oral Contraceptive (Estrogens): Barbiturates may diminish the therapeutic effect of Oral Contraceptive (Estrogens). Contraceptive failure is possible. Risk D: Consider therapy modification

Primidone: May enhance the adverse/toxic effect of Barbiturates. Primidone is converted to phenobarbital, and thus becomes additive with existing barbiturate therapy. Risk C: Monitor therapy

Propafenone: Barbiturates may increase the metabolism of Propafenone. Risk D: Consider therapy modification

Pyridoxine: May increase the metabolism of Barbiturates. Apparent in high pyridoxine doses (eg, 200 mg/day) Risk C: Monitor therapy

QuiNIDine: Barbiturates may increase the metabolism of QuiNIDine. Risk D: Consider therapy modification

Rifamycin Derivatives: May increase the metabolism of Barbiturates. Risk C: Monitor therapy

Teniposide: Barbiturates may increase the metabolism of Teniposide. Risk C: Monitor therapy

Theophylline Derivatives: Barbiturates may increase the metabolism of Theophylline Derivatives. Exceptions: Dyphylline. Risk C: Monitor therapy

Thiazide Diuretics: Barbiturates may enhance the orthostatic effect of Thiazide Diuretics. Risk C: Monitor therapy

Tricyclic Antidepressants: Barbiturates may increase the metabolism of Tricyclic Antidepressants. Risk D: Consider therapy modification

Valproic Acid: May decrease the metabolism of Barbiturates. Barbiturates may decrease the serum concentration of Valproic Acid. Risk C: Monitor therapy

Vitamin K Antagonists (eg, warfarin): Barbiturates may increase the metabolism of Vitamin K Antagonists. Risk D: Consider therapy modification

Voriconazole: Barbiturates may decrease the serum concentration of Voriconazole. Risk X: Avoid combination

ETHANOL / NUTRITION / HERB INTERACTIONS — Ethanol: Avoid ethanol (may increase CNS depression).

PREGNANCY RISK FACTOR — D (show table)

PREGNANCY IMPLICATIONS — Barbiturates cross the placenta and distribute in fetal tissue. Teratogenic effects have been reported with 1st trimester exposure. Exposure during the 3rd trimester may lead to symptoms of acute withdrawal following delivery; symptoms may be delayed up to 14 days.

LACTATION — Excretion in breast milk unknown/use caution

BREAST-FEEDING CONSIDERATIONS — Small amounts of barbiturates are excreted in breast milk; information specific for amobarbital is not available.

MONITORING PARAMETERS — Vital signs should be monitored during injection and for several hours after administration.

REFERENCE RANGE
Therapeutic: 1-5 mcg/mL (SI: 4-22 µmol/L)

Toxic: >10 mcg/mL (SI: >44 µmol/L)

Lethal: >50 mcg/mL

CANADIAN BRAND NAMES — Amytal®

INTERNATIONAL BRAND NAMES — Amybital (TW); Amycal (NO); Amytal Sodium (AU); Barbamyl (IL); Dorlotin (HU); Dorlotyn (HU); Eunoctal (FR); Isoamitil Sedante (ES); Isomytal (JP); Neur-Amyl (AU); Placidel (ES); Sodium Amytal (GB); Transital (ES)

MECHANISM OF ACTION — Interferes with transmission of impulses from the thalamus to the cortex of the brain resulting in an imbalance in central inhibitory and facilitatory mechanisms

PHARMACODYNAMICS / KINETICS
Onset of action: I.V.: Within 5 minutes

Distribution: Readily crosses placenta; small amounts enter breast milk

Metabolism: Primarily hepatic via microsomal enzymes

Half-life elimination: 15-40 hours (mean: 25 hours)

Excretion: Urine, feces