Amobarbital is an intermediate-acting barbiturate that depresses the sensory cortex, decreases motor activity, and alter cerebellar function producing sedation, drowsiness, and hypnosis.

It is used as a sedative, hypnotic, or as a pre-anesthetic.

It is also used as an off-label treatment for diagnostic and therapeutic purposes in amytal interviewing (Wada test) for psychiatric purposes. 

Amobarbital Dose in Adults

Dose for use as a Hypnotic:

• 65 - 200 mg intramuscular or intravenous at bedtime to a maximum single dose of 1,000 mg)

Use as a Sedative:

• 30 - 50 mg intramuscular or intravenous 2 - 3 times a day to the maximum single dose of 1,000 mg.

Off label use in the “Amytal interview”:

• 50 - 100 mg/minute intravenous for a total dose of 200 - 1,000 mg or until the patient experiences drowsiness, develops slurred speech, nystagmus, or impaired attention.

Off Label use in the Wada test:

• 60 - 200 mg intracarotid (usual dose: 125 mg) over 2 - 5 seconds via a percutaneous transfemoral catheter (the usual dose is 125 mg)
• The dose may be repeated after 30 - 45 minutes of completion of the first injection.

Amobarbital Dose in Childrens

Hypnotic as in preoperative sedation:

• Children older than 6 years and Adolescents:
  • 2 - 3 mg/kg/dose to a maximum dose of 500 mg/dose intramuscular (preferred) or intravenous.

Intracarotid amobarbital procedure (Wada test):

• Children older than 6 years and Adolescents:
  • 75 - 125 mg/dose intraarterial administered through femoral arterial catheter.

Pregnancy Risk Factor D

• If administered in the first trimester, barbiturates can cross the placental barriers and cause teratogenic reactions.
• The third trimester administration may cause symptoms of withdrawal after delivery, lasting up to 14 days.

Amobarbital during breastfeeding:

• Breastfeeding is a good time to avoid it. Breast milk contains small amounts of barbiturates.

Amobarbital Dose in Renal Disease:

• Adjustment in the dose has not been recommended by the manufacturer.
• The dose may need adjustment in renal disease. 

Amobarbital Dose in Liver Disease:

• Adjustment in the dose has not been recommended by the manufacturer.
• It should be avoided in severe hepatic impairment and the dose should be adjusted in mild to moderate hepatic impairment.

Amobarbital side effects:

• Cardiovascular:
  • Bradycardia
  • Hypotension
  • Syncope
• Central Nervous System:
  • Abnormality In Thinking
  • Agitation
  • Anxiety
  • Ataxia
  • Central Nervous System Depression
  • Confusion
  • Dizziness
  • Drowsiness
  • Hallucination
  • Headache
  • Insomnia
  • Nervousness
  • Nightmares
  • Psychiatric Disturbance
• Gastrointestinal:
  • Constipation
  • Nausea
  • Vomiting
• Hematologic & Oncologic:
  • Megaloblastic Anemia with chronic use
• Hepatic:
  • Hepatic Injury
• Hypersensitivity:
  • Hypersensitivity Reaction
    • Angioedema
    • Skin Rash
    • Exfoliative Dermatitis
• Local:
  • Injection Site Reaction
• Neuromuscular & Skeletal:
  • Hyperkinesia
• Respiratory:
  • Apnea
  • Atelectasis
  • Hypoventilation
• Miscellaneous:
  • Fever

Contraindication to Amobarbital Include:

• Allergy to barbiturates and any component of the formulation
• Patients with porphyria
• Advanced liver disease
• Patients suffering from a severe or moderately severe respiratory condition that is complicated by hypoxemia or hypercapnia.

Warnings and Precautions

• CNS depression:
  • CNS depression can occur in patients who use heavy machinery or those who perform tasks that require mental abilities above average.
• Paradoxical responses:
  • Patients with chronic/ acute pain may feel a paradoxical sense of excitement.
• Depression
  • Patients suffering from depression or suicidal tendencies must be cautious when taking the drug.
• Use of drugs:
  • Tolerance, psychological and physical dependence may develop from prolonged use.
  • Patients who have a history or potential for drug abuse should be cautious about using the drug.
• Hepatic impairment
  • It is contraindicated for patients with severe hepatic impairment or impending hepatic disease.
  • Patients suffering from mild or moderate hepatic dysfunction might need to reduce their dose.
• Hypoadrenalism
  • Hypoadrenal patients should not use it.
  • The effects of glucocorticoids may be diminished by its use.
• Renal impairment
  • Dose adjustment may be necessary for patients with impaired renal function.
  • Patients with kidney disease should use it with caution.
• Respiratory disease
  • It can cause respiratory depression so patients suffering from respiratory disease should not use it.

Amobarbital: Drug Interaction

Note: Drug Interaction Categories:

• Risk Factor C: Monitor When Using Combination
• Risk Factor D: Consider Treatment Modification
• Risk Factor X: Avoid Concomitant Use

Monitor:

• Renal funcitons and hepatic functions with prolonged therapy.
• Vital signs and cardiac function should be monitored during intravenous administration.

How to administer Amobarbital?

• Intramuscular administration:
  • It should be administered deep into a large muscle. It may cause tissue damage if more than 5 ml is administered at any single site.
  • For administration of larger doses, use 20% solution.
  • Subcutaneous administration and superficial intramuscular injections may be painful and produce sterile abscesses or sloughs.
• Intravenous administration:
  • It should be used only when the intramuscular administration is not feasible.
  • Intravenous injection should be administered by a slow intravenous injection at a maximum rate of 50 mg/min in adults.
• Intra-carotid administration as off-label route (Wada test):
  • Administer the dose over 2 - 5 seconds into the internal carotid artery via a percutaneous transfemoral catheter.

Mechanism of action of Amobarbital:

It is a intermediate-acting barbiturate, which depresses sensory cortex, decreases motor activation, alters cerebellar function, and produces sedation, somnolence, and hypnosis.

It has been aRapid onset of actionVariable (within minutes)Duration of actionIt is primarilyMetabolizedVia the liver (microsomal enzymes).

It has been ahalf-life eliminationBetween 16 and 40 hours Themaximum effectIt can be seen in just hours.

 It isexcretedThe metabolites are mainly found in the urine. They are excreted in your feces.

International Brands of Amobarbital:

• Amital
• Amybital
• Amycal
• Amytal
• Amytal Sodium
• Barbamyl
• Eunoctal
• Isomytal
• Neur-Amyl
• Sodium Amytal

Amobarbital Brands in Pakistan:

 No brands available in Pakistan.