Amobarbital


Generic Medicine Info
Indications and Dosage
Oral
Severe intractable insomnia
Adult: 100-200 mg at bedtime. As amobarbital Na: 60-200 mg at bedtime.
Elderly: Reduce dose.

Parenteral
Hypnotic
Adult: 65-200 mg via IM inj (should not exceed 5 mL at any single site) or IV inj (should not exceed 50 mg/min) at bedtime. Max: 1,000 mg as a single dose.
Elderly: Reduce dose.

Parenteral
Sedation
Adult: As amobarbital Na: 30-50 mg via IM inj (should not exceed 5 mL at any single site) or IV inj (should not exceed 50 mg/min) given 2-3 times daily. Max: 1,000 mg as a single dose.
Child: 6-12 yr 65-500 mg.
Elderly: Reduce dose.
Special Patient Group
Debilitated patient: Reduce dose.
Renal Impairment
Reduce dose.
Hepatic Impairment
Reduce dose. Severe: Contraindicated.
Administration
May be taken with or without food.
Reconstitution
Reconstitute 500 mg sterile powd for inj in 5 mL sterile water for inj to make a 10% IV soln. Reconstitute 500 mg sterile powd for inj in 2.5 mL of sterile water for inj to make 20% IM soln. Rotate vial to dissolve; do not shake.
Incompatibility
Incompatible w/ acidic soln. Syringe: Thiamine.
Contraindications
Dyspnoea or airway obstruction, porphyria, sleep apnoea, pre-existing CNS depression or coma. Severe hepatic impairment.
Special Precautions
Patient w/ CV disease, depression or suicidal ideation, history of drug addiction or acute alcoholism. Renal and mild to moderate hepatic impairment. Elderly and debilitated patients, childn. Pregnancy and lactation.
Adverse Reactions
Bradycardia, syncope, hypotension; apnoea, atelectasis (post-op), hypoventilation; agitation, anxiety, ataxia, confusion, CNS depression, dizziness, fever, hallucinations, headache, insomnia, nightmares, nervousness, psychiatric disturbances, somnolence, abnormal thinking; hyperkinesias; nausea, vomiting, constipation; liver damage; megaloblastic anaemia (following chronic phenobarbital use); angioedema, rash; inj site reaction.
Potentially Fatal: Erythema multiforme and exfoliative dermatitis.
IM/IV/Parenteral/PO: D
Patient Counseling Information
May impair mental or physical abilities requiring mental alertness (e.g. driving or operating machinery).
Monitoring Parameters
Monitor vital signs during and after admin.
Overdosage
Symptoms: CNS depression, absent or sluggish reflexes, underventilation, hypotension, hypothermia, pulmonary oedema, haemorrhagic blisters. Management: Secure airway, support ventilation and perfusion. Admin activated charcoal. Perform haemodialysis and haemoperfusion in serious cases.
Drug Interactions
May reduce plasma levels of oral anticoagulants (e.g. warfarin, dicoumarol, acenocoumarol, phenprocoumon), corticosteroids, griseofulvin, doxycycline, Na valproate and valproic acid. Constant monitoring of blood levels when concomitantly used w/ phenytoin. May increase CNS depressant effect w/ antihistamines, sedative/hypnotics, tranquilisers. May prolong the effect w/ MAOIs. May reduce the effect of estradiol, progesterone, estrone and other steroidal hormones.
Food Interaction
May enhance CNS depressant effect of alcohol.
Action
Description: Amobarbital interferes w/ the transmission of impulses from the thalamus to the cortex of the brain which develops an imbalance in central inhibitory and facilitatory mechanisms.
Onset: W/in 5 min (IV).
Pharmacokinetics:
Absorption: Readily absorbed from the GI tract.
Distribution: Rapidly distributed to all tissues and fluids; crosses the placenta; enters breast milk (small amounts). Plasma protein binding: Approx 60%.
Metabolism: Undergoes hepatic metabolism via penultimate oxidation of the 3-methylbutyl substituent forming a tertiary alcohol, hydroxyamobarbital (inactive metabolite).
Excretion: Via urine (approx 50% as 3'-hydroxyamylobarbital, approx 30% as N-hydroxyamylobarbital, <1% as unchanged drug); faeces (approx 5%). Half-life: Approx 40 min (1st phase); approx 20-25 hr (2nd phase).
Chemical Structure

Chemical Structure Image
Amobarbital

Source: National Center for Biotechnology Information. PubChem Database. Amobarbital, CID=2164, https://pubchem.ncbi.nlm.nih.gov/compound/Amobarbital (accessed on Jan. 20, 2020)

Storage
Powd: Store between 15-30°C.
References
Amytal Sodium Injection, Powder, Lyophilized, for Solution (Marathon Pharmaceuticals, LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 10/11/2014.

Anon. Amobarbital. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 10/11/2014.

Buckingham R (ed). Amobarbital. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 10/11/2014.

McEvoy GK, Snow EK, Miller J et al (eds). Amobarbital, Amobarbital Sodium. AHFS Drug Information (AHFS DI) [online]. American Society of Health-System Pharmacists (ASHP). https://www.medicinescomplete.com. Accessed 10/11/2014.

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