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Amobarbital

Medically reviewed by Drugs.com. Last updated on Sep 18, 2023.

Pronunciation

(am oh BAR bi tal)

Index Terms

Dosage Forms

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

Solution Reconstituted, Injection, as sodium:

Amytal Sodium: 500 mg (1 ea)

Detailed Amobarbital dosage information

Brand Names: U.S.

Pharmacologic Category

Pharmacology

An intermediate-acting barbiturate; barbiturates depress the sensory cortex, decrease motor activity, and alter cerebellar function producing drowsiness, sedation, and hypnosis.

Metabolism

Primarily hepatic via microsomal enzymes

Excretion

Urine (as metabolites, negligible amounts excreted unchanged in urine); feces (metabolites)

Onset of Action

Rapid, within minutes

Time to Peak

Maximum effect: Hours

Duration of Action

Variable

Half-Life Elimination

16 to 40 hours (mean: 25 hours)

Use: Labeled Indications

Sedative/hypnotic: Use as a sedative, hypnotic, or preanesthetic

Off Label Uses

Therapeutic or diagnostic “Amytal Interviewing” for psychiatric conditions

Data from a limited number of clinical trials suggest that amobarbital may be beneficial for therapeutic or diagnostic “Amytal Interviewing” for psychiatric conditions [Kavirajan 1999]. Additional data may be necessary to further define the role of amobarbital in this setting.

Wada test

Data from a limited number of clinical trials suggest that amobarbital may be beneficial for determining cerebral dominance to predict the likelihood of a catastrophic memory outcome after surgical resection for the treatment of epilepsy [Acharya 1997], [Patel 2011]. However, more recent evidence suggests the test has less than ideal reliability and validity, and it may pose some risk. Some suggest the intracarotid amobarbital procedure be reserved for patients with atypical or bilateral language representation and when functional MRI is inconclusive [Sharan 2011].

Contraindications

Hypersensitivity to barbiturates or any component of the formulation; history of manifest or latent porphyria; marked liver function impairment; marked respiratory disease in which dyspnea or obstruction is evident.

Dosing: Adult

Hypnotic: IM, IV: 65 to 200 mg at bedtime (maximum single dose: 1,000 mg)

Sedative: IM, IV: 30 to 50 mg 2 or 3 times daily (maximum single dose: 1,000 mg)

“Amytal interview” (off-label use): IV: 50 to 100 mg/minute for total dose of 200 to 1,000 mg or until patient experiences drowsiness, impaired attention, slurred speech, or nystagmus (Kavirajan 1999)

Wada test (off-label use): Intra-carotid: 60 to 200 mg (usual dose: 125 mg) over 2 to 5 seconds via percutaneous transfemoral catheter; after 30 to 45 minutes has elapsed since completion of first injection, may repeat dose for evaluation of contralateral hemisphere (Acharya 1997; Patel 2011). Note: Due to the adverse effects associated with intra-carotid amobarbital and questionable reliability and validity, other less invasive tests (eg, functional MRI) may be recommended (Sharan 2011).

Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.

Dosing: Geriatric

Avoid use (Beers Criteria [AGS 2019]).

Dosing: Pediatric

Note: Dosage should be individualized with consideration of patient's age, weight, and medical condition. Use of amobarbital as a sedative and as a hypnotic for the treatment of insomnia and as a hypnotic for preoperative sedation has been replaced by newer agents.

Hypnotic (eg, preoperative sedation): Children ≥6 years and Adolescents: IM (preferred), IV: Usual recommendation (Limited data available): 2 to 3 mg/kg/dose; maximum dose: 500 mg/dose; dosing based on generally recognized expert recommendations; published pediatric trial data is lacking (Nelson 1996). The manufacturer describes the ordinary dose range in children 6 to 12 years as 65 to 500 mg and specific dosing recommendations based on patient size are not available; however, in several instances, this may exceed expert weight-based recommendations; if using manufacturer dosing, initiate therapy at the lower end of the range and titrate the dose accordingly.

Intracarotid amobarbital procedure (Wada test): Limited data available; dosing regimens variable: Children ≥6 years and Adolescents: Intra-arterial: 75 to 125 mg/dose; typically administered through femoral arterial catheter; consult institution specific protocols (Acharay 1997; Burns 2009; Hinz 1994; Kim 2007; Szabo 1993)

Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.

Reconstitution

Reconstitute with 50 mL SWFI to make a 1% solution; 20 mL SWFI to make a 2.5% solution; 10 mL SWFI to make a 5% solution; 5 mL of SWFI to make a 10% solution; 2.5 mL SWFI to make a 20% solution. The 10% solution is ordinarily used; the 20% solution may be used so that a small volume contains a large dose. Rotate vial to dissolve, do not shake. Do not use unless a clear solution forms within 5 minutes; a solution that forms a precipitate after clearing should not be used. Not more than 30 minutes should elapse from the time the vial is opened until its contents are injected.

Administration

IM: Administer deeply into a large muscle. Do not use more than 5 mL (irrespective of concentration) at any single site (may cause tissue damage). Use 20% solution to facilitate larger doses. Superficial IM or subcutaneous injections may be painful and produce sterile abscesses or sloughs.

IV: Use only when IM administration is not feasible. Administer by slow IV injection (maximum rate of infusion: 50 mg/minute in adults). May administer up to 100 mg/minute when performing “Amytal interview” (off-label use; Kavirajan 1999).

Intra-carotid (off-label route): Wada test (off-label use): Administer dose over 2 to 5 seconds via percutaneous transfemoral catheter into the internal carotid artery (Acharya 1997).

Storage

Store intact vials at 15°C to 30°C (59°F to 86°F). Following reconstitution, solution should be used within 30 minutes.

Drug Interactions

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

Alizapride: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Azelastine (Nasal): May enhance the CNS depressant effect of CNS Depressants. Avoid combination

Beta-Blockers: Barbiturates may decrease the serum concentration of Beta-Blockers. Monitor therapy

Blonanserin: CNS Depressants may enhance the CNS depressant effect of Blonanserin. Management: Use caution if coadministering blonanserin and CNS depressants; dose reduction of the other CNS depressant may be required. Strong CNS depressants should not be coadministered with blonanserin. Consider therapy modification

Blood Pressure Lowering Agents: Barbiturates may enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Brexanolone: CNS Depressants may enhance the CNS depressant effect of Brexanolone. Monitor therapy

Brimonidine (Topical): May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Bromopride: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Bromperidol: May enhance the CNS depressant effect of CNS Depressants. Avoid combination

Buprenorphine: CNS Depressants may enhance the CNS depressant effect of Buprenorphine. Management: Consider reduced doses of other CNS depressants, and avoiding such drugs in patients at high risk of buprenorphine overuse/self-injection. Initiate buprenorphine at lower doses in patients already receiving CNS depressants. Consider therapy modification

Calcium Channel Blockers: Barbiturates may increase the metabolism of Calcium Channel Blockers. Management: Monitor for decreased therapeutic effects of calcium channel blockers with concomitant barbiturate therapy. Calcium channel blocker dose adjustments may be necessary. Nimodipine Canadian labeling contraindicates concomitant use with phenobarbital. Monitor therapy

Cannabidiol: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Cannabis: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Chloramphenicol (Systemic): May decrease the metabolism of Barbiturates. Barbiturates may increase the metabolism of Chloramphenicol (Systemic). Monitor therapy

Chlormethiazole: May enhance the CNS depressant effect of CNS Depressants. Management: Monitor closely for evidence of excessive CNS depression. The chlormethiazole labeling states that an appropriately reduced dose should be used if such a combination must be used. Consider therapy modification

Chlorphenesin Carbamate: May enhance the adverse/toxic effect of CNS Depressants. Monitor therapy

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

Dimethindene (Topical): May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Doxycycline: Barbiturates may decrease the serum concentration of Doxycycline. Monitor therapy

Doxylamine: May enhance the CNS depressant effect of CNS Depressants. Management: The manufacturer of Diclegis (doxylamine/pyridoxine), intended for use in pregnancy, specifically states that use with other CNS depressants is not recommended. Monitor therapy

Dronabinol: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Droperidol: May enhance the CNS depressant effect of CNS Depressants. Management: Consider dose reductions of droperidol or of other CNS agents (eg, opioids, barbiturates) with concomitant use. Consider therapy modification

Esketamine: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Estrogen Derivatives (Contraceptive): Barbiturates may diminish the therapeutic effect of Estrogen Derivatives (Contraceptive). Contraceptive failure is possible. Management: Use of a non-hormonal contraceptive is recommended. Breakthrough bleeding, though an important sign regarding the diminished effect of oral contraceptives, might not be present in spite of the occurrence of an interaction. Consider therapy modification

Felbamate: May increase the serum concentration of Barbiturates. Barbiturates may decrease the serum concentration of Felbamate. Management: Monitor for elevated barbiturate concentrations/toxicity if felbamate is initiated/dose increased, or reduced concentrations/effects if felbamate is discontinued/dose decreased. Refer to phenobarbital dosing guidelines for patients receiving that agent. Monitor therapy

Flunitrazepam: CNS Depressants may enhance the CNS depressant effect of Flunitrazepam. Management: Reduce the dose of CNS depressants when combined with flunitrazepam and monitor patients for evidence of CNS depression (eg, sedation, respiratory depression). Use non-CNS depressant alternatives when available. Consider therapy modification

Griseofulvin: Barbiturates may decrease the serum concentration of Griseofulvin. Monitor therapy

Hemin: Barbiturates may diminish the therapeutic effect of Hemin. Avoid combination

HydrOXYzine: May enhance the CNS depressant effect of Barbiturates. Management: Consider a decrease in the barbiturate dose, as appropriate, when used together with hydroxyzine. With concurrent use, monitor patients closely for excessive response to the combination. Consider therapy modification

Kava Kava: May enhance the adverse/toxic effect of CNS Depressants. Monitor therapy

Lemborexant: May enhance the CNS depressant effect of CNS Depressants. Management: Dosage adjustments of lemborexant and of concomitant CNS depressants may be necessary when administered together because of potentially additive CNS depressant effects. Close monitoring for CNS depressant effects is necessary. Consider therapy modification

Lisuride: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Lofexidine: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Magnesium Sulfate: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Methotrimeprazine: CNS Depressants may enhance the CNS depressant effect of Methotrimeprazine. Methotrimeprazine may enhance the CNS depressant effect of CNS Depressants. Management: Reduce the usual dose of CNS depressants by 50% if starting methotrimeprazine until the dose of methotrimeprazine is stable. Monitor patient closely for evidence of CNS depression. Consider therapy modification

Methoxyflurane: Barbiturates may enhance the nephrotoxic effect of Methoxyflurane. Barbiturates may increase the metabolism of Methoxyflurane. Avoid combination

Metoclopramide: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

MetyroSINE: CNS Depressants may enhance the sedative effect of MetyroSINE. Monitor therapy

Mianserin: May enhance the CNS depressant effect of Barbiturates. Mianserin may diminish the therapeutic effect of Barbiturates. Barbiturates may decrease the serum concentration of Mianserin. Avoid combination

Minocycline (Systemic): May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Multivitamins/Minerals (with ADEK, Folate, Iron): May decrease the serum concentration of Barbiturates. Monitor therapy

Nabilone: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Opioid Agonists: CNS Depressants may enhance the CNS depressant effect of Opioid Agonists. Management: Avoid concomitant use of opioid agonists and benzodiazepines or other CNS depressants when possible. These agents should only be combined if alternative treatment options are inadequate. If combined, limit the dosages and duration of each drug. Consider therapy modification

Orphenadrine: CNS Depressants may enhance the CNS depressant effect of Orphenadrine. Avoid combination

Oxomemazine: May enhance the CNS depressant effect of CNS Depressants. Avoid combination

Oxybate Salt Products: CNS Depressants may enhance the CNS depressant effect of Oxybate Salt Products. Management: Consider alternatives to this combination when possible. If combined, dose reduction or discontinuation of one or more CNS depressants (including the oxybate salt product) should be considered. Interrupt oxybate salt treatment during short-term opioid use Consider therapy modification

OxyCODONE: CNS Depressants may enhance the CNS depressant effect of OxyCODONE. Management: Avoid concomitant use of oxycodone and benzodiazepines or other CNS depressants when possible. These agents should only be combined if alternative treatment options are inadequate. If combined, limit the dosages and duration of each drug. Consider therapy modification

Paraldehyde: CNS Depressants may enhance the CNS depressant effect of Paraldehyde. Avoid combination

Perampanel: May enhance the CNS depressant effect of CNS Depressants. Management: Patients taking perampanel with any other drug that has CNS depressant activities should avoid complex and high-risk activities, particularly those such as driving that require alertness and coordination, until they have experience using the combination. Consider therapy modification

Piribedil: CNS Depressants may enhance the CNS depressant effect of Piribedil. Monitor therapy

Pramipexole: CNS Depressants may enhance the sedative effect of Pramipexole. Monitor therapy

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

Progestins (Contraceptive): Barbiturates may diminish the therapeutic effect of Progestins (Contraceptive). Contraceptive failure is possible. Management: Use of alternative, nonhormonal contraceptives is recommended. When using levonorgestrel as emergency contraception, non-US guidelines suggest doubling the dose of levonorgestrel to 3 mg in women who have used enzyme inducing drugs in the past 4 weeks. Consider therapy modification

Propacetamol: Barbiturates may increase the metabolism of Propacetamol. This may 1) diminish the desired effects of propacetamol; and 2) increase the risk of liver damage. Monitor therapy

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

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

ROPINIRole: CNS Depressants may enhance the sedative effect of ROPINIRole. Monitor therapy

Rotigotine: CNS Depressants may enhance the sedative effect of Rotigotine. Monitor therapy

Rufinamide: May enhance the adverse/toxic effect of CNS Depressants. Specifically, sleepiness and dizziness may be enhanced. Monitor therapy

Somatostatin Acetate: May enhance the adverse/toxic effect of Barbiturates. Specifically, Somatostatin Acetate may enhance or prolong Barbiturate effects, including sedative effects. Avoid combination

Suvorexant: CNS Depressants may enhance the CNS depressant effect of Suvorexant. Management: Dose reduction of suvorexant and/or any other CNS depressant may be necessary. Use of suvorexant with alcohol is not recommended, and the use of suvorexant with any other drug to treat insomnia is not recommended. Consider therapy modification

Teniposide: Barbiturates may decrease the serum concentration of Teniposide. Management: Consider alternatives to combined treatment with barbiturates and teniposide due to the potential for decreased teniposide concentrations. If the combination cannot be avoided, monitor teniposide response closely. Consider therapy modification

Tetrahydrocannabinol: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Tetrahydrocannabinol and Cannabidiol: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Thalidomide: CNS Depressants may enhance the CNS depressant effect of Thalidomide. Avoid combination

Theophylline Derivatives: Barbiturates may decrease the serum concentration of Theophylline Derivatives. Monitor therapy

Tricyclic Antidepressants: Barbiturates may increase the metabolism of Tricyclic Antidepressants. Management: Monitor for decreased efficacy of tricyclic antidepressants if a barbiturate is initiated/dose increased, or increased effects if a barbiturate is discontinued/dose decreased. Tricyclic antidepressant dose adjustments are likely required. Consider therapy modification

Trimeprazine: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Ulipristal: Barbiturates may decrease the serum concentration of Ulipristal. Avoid combination

Valproate Products: May increase the serum concentration of Barbiturates. Barbiturates may decrease the serum concentration of Valproate Products. Monitor therapy

Vitamin K Antagonists (eg, warfarin): Barbiturates may increase the metabolism of Vitamin K Antagonists. Management: Monitor INR more closely. Anticoagulant dose increases of 30% to 60% may be needed after a barbiturate is initiated or given at an increased dose. Anticoagulant dose decreases may be needed following barbiturate discontinuation or dose reduction. Consider therapy modification

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

Zolpidem: CNS Depressants may enhance the CNS depressant effect of Zolpidem. Management: Reduce the Intermezzo brand sublingual zolpidem adult dose to 1.75 mg for men who are also receiving other CNS depressants. No such dose change is recommended for women. Avoid use with other CNS depressants at bedtime; avoid use with alcohol. Consider therapy modification

Amobarbital drug interactions (more detail)

Adverse Reactions

The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified. Frequency not defined and is reported as barbiturate use (not specifically amobarbital).

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 (following chronic phenobarbital use)

Hepatic: Hepatic injury

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

Local: Injection site reaction

Neuromuscular & skeletal: Hyperkinesia

Respiratory: Apnea, atelectasis (postoperative), hypoventilation

Miscellaneous: Fever

Amobarbital side effects (more detail)

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).

• Paradoxical responses: May cause paradoxical excitement, particularly in patients with acute or chronic pain.

Disease-related concerns:

• Depression: Use with caution, if at all, in patients with depression or suicidal tendencies.

• Drug abuse: Use with caution, if at all, 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. Do not administer to patients showing premonitory signs of hepatic coma.

• Hypoadrenalism: Use with caution in patients with borderline hypoadrenal function; even if it is of pituitary or of primary adrenal origin. Systemic effects of exogenous and endogenous corticosteroids may be diminished by amobarbital.

• Renal impairment: Use with caution in patients with renal impairment; decreased dosage may be needed.

• Respiratory disease: Use with caution in patients with respiratory disease; may cause respiratory depression.

Special populations:

• Debilitated patient: Use with caution in debilitated patients; may react to barbiturates with marked excitement, depression, and confusion; reduced dosages are recommended.

• Pediatric: Barbiturates repeatedly produce excitement rather than depression in some patients, particularly children.

Dosage form specific issues:

• Alkaline solution: Solution for injection is highly alkaline and extravasation may cause local tissue damage with subsequent necrosis.

Other warnings/precautions:

• Appropriate use: When used as a hypnotic for the treatment of insomnia, effectiveness is limited to ≤2 weeks.

• Administration: Rapid IV administration may cause respiratory depression, apnea, laryngospasm, or vasodilation with a fall in blood pressure; avoid perivascular extravasation or intra-arterial injection; discontinue if patient complains of pain in the limb. Restrict use of IV administration to conditions in which other routes are not feasible, if patient is unconscious (eg, cerebral hemorrhage, eclampsia, or status epilepticus) or patient resists (eg, delirium), or because prompt action is imperative.

• Withdrawal: Abrupt cessation may precipitate withdrawal, including delirium and convulsions (some fatal); withdraw gradually.

Monitoring Parameters

Vital signs and cardiac function during IV administration) renal, and hepatic function with prolonged therapy.

Pregnancy Risk Factor D Pregnancy Considerations

Barbiturates cross the placenta and distribute in fetal tissue. Teratogenic effects have been reported with first trimester exposure. Exposure during the third trimester may lead to symptoms of acute withdrawal following delivery; symptoms may be delayed up to 14 days.

Patient Education

What is this drug used for?

• It is used to treat sleep problems.

• It is used to calm you before a procedure.

• It may be given to you for other reasons. Talk with the doctor.

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

• Fatigue

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

• Trouble breathing

• Slow breathing

• Shallow breathing

• Mood changes

• Behavioral changes

• Depression

• Suicidal ideation

• Injection site redness, burning, pain, swelling, blisters, skin sores, or leaking of fluid

• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.

Note: This is not a comprehensive list of all side effects. Talk to your doctor if you have questions.

Consumer Information Use and Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a limited summary of general information about the medicine's uses from the patient education leaflet and is not intended to be comprehensive. This limited summary does NOT include all information available about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not intended to provide medical advice, diagnosis or treatment and does not replace information you receive from the healthcare provider. For a more detailed summary of information about the risks and benefits of using this medicine, please speak with your healthcare provider and review the entire patient education leaflet.

Further information

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