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Amobarbital

Pronunciation

(am oh BAR bi tal)

Index Terms

  • Amobarbital Sodium
  • Amylobarbitone

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)

Brand Names: U.S.

  • Amytal Sodium

Pharmacologic Category

  • Barbiturate

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

Use: Unlabeled

Therapeutic or diagnostic “Amytal® Interviewing”; Wada test

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).

Dosing: Geriatric

Avoid use due to risk of overdose with low dosages, tolerance to sleep effects, and increased risk of physical dependence (Beers Criteria).

Dosing: Pediatric

Sedative, hypnotic: Children ≥6 years and Adolescents: IM (preferred), IV: 2 to 3 mg/kg/dose; maximum dose: 500 mg/dose (AHFS 2015; McEvoy 1993; 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.

Dosing: Renal Impairment

There are no dosage adjustments provided in the manufacturer’s labeling; reduced doses are recommended.

Dosing: Hepatic Impairment

There are no dosage adjustments provided in the manufacturer’s labeling; reduced doses are recommended.

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).

Compatibility

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

Compatibility in syringe: Incompatible with thiamine.

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

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

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

Blonanserin: CNS Depressants may enhance the CNS depressant effect of Blonanserin. Consider therapy modification

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

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

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 patches (Butrans brand) at 5 mcg/hr in adults when used with other 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. Exceptions: Clevidipine. Monitor therapy

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

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

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

Contraceptives (Estrogens): Barbiturates may diminish the therapeutic effect of Contraceptives (Estrogens). Contraceptive failure is possible. Management: Use of a non-hormonal contraceptive is recommended. Consider therapy modification

Contraceptives (Progestins): Barbiturates may diminish the therapeutic effect of Contraceptives (Progestins). Contraceptive failure is possible. Management: Use of alternative, nonhormonal contraceptives is recommended. Consider therapy modification

CycloSPORINE (Systemic): Barbiturates may increase the metabolism of CycloSPORINE (Systemic). Consider therapy modification

CYP2A6 Substrates: CYP2A6 Inducers (Strong) may increase the metabolism of CYP2A6 Substrates. Management: Consider an alternative for one of the interacting drugs. Some combinations may be specifically contraindicated. Consult appropriate manufacturer labeling. Consider therapy modification

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

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

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 (e.g., opioids, barbiturates) with concomitant use. 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. 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

HYDROcodone: CNS Depressants may enhance the CNS depressant effect of HYDROcodone. Management: Consider starting with a 20% to 30% lower hydrocodone dose when using together with any other CNS depressant. Dose reductions in the other CNS depressant may also be warranted. Consider therapy modification

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

LamoTRIgine: Barbiturates may decrease the serum concentration of LamoTRIgine. Management: See lamotrigine prescribing information for specific age-dependent dosing guidelines regarding concurrent use with a barbiturate, as well as for adjusting lamotrigine dosing if concurrent barbiturate therapy is discontinued. Consider therapy modification

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

Meperidine: Barbiturates may enhance the CNS depressant effect of Meperidine. Barbiturates may increase serum concentrations of the active metabolite(s) of Meperidine. 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 adult dose of CNS depressant agents by 50% with initiation of concomitant methotrimeprazine therapy. Further CNS depressant dosage adjustments should be initiated only after clinically effective methotrimeprazine dose is established. Consider therapy modification

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

Mirtazapine: CNS Depressants may enhance the CNS depressant effect of Mirtazapine. 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

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

OxyCODONE: CNS Depressants may enhance the CNS depressant effect of OxyCODONE. Management: When oxycodone is combined with another CNS depressant, a dose reduction of one or both agents should be considered. The extended release oxycodone starting dose should be reduced 50% to 67% when initiated in patients already receiving CNS depressants. 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 [INT]: CNS Depressants may enhance the CNS depressant effect of Piribedil [INT]. 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

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

Selective Serotonin Reuptake Inhibitors: CNS Depressants may enhance the adverse/toxic effect of Selective Serotonin Reuptake Inhibitors. Specifically, the risk of psychomotor impairment may be enhanced. Monitor therapy

Sodium Oxybate: May enhance the CNS depressant effect of CNS Depressants. Management: Consider alternatives to combined use. When combined use is needed, consider minimizing doses of one or more drugs. Use of sodium oxybate with alcohol or sedative hypnotics is contraindicated. Consider therapy modification

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

Tapentadol: May enhance the CNS depressant effect of CNS Depressants. Management: Start tapentadol at a dose of one-third to one-half of the normal dose if being initiated in a patient who is taking another drug with CNS depressant effects. Monitor closely for evidence of excessive CNS depression. 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

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

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

Thiazide and Thiazide-Like Diuretics: Barbiturates may enhance the orthostatic hypotensive effect of Thiazide and Thiazide-Like Diuretics. Monitor therapy

Tricyclic Antidepressants: Barbiturates may increase the metabolism of Tricyclic Antidepressants. 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. An anticoagulant dose increase 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

Adverse Reactions

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

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.

Concurrent drug therapy issues:

• Drug-drug interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.

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 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.

Patient Education

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience loss of strength and energy or fatigue. Have patient report immediately to prescriber signs of depression (suicidal ideation, anxiety, emotional instability, or confusion), signs of liver problems (dark urine, fatigue, lack of appetite, nausea, abdominal pain, light-colored stools, vomiting, or jaundice), shortness of breath, difficulty breathing, slow breathing, shallow breathing, change in balance, confusion, hallucinations, anxiety, insomnia, severe dizziness, passing out, bradycardia, abnormal heartbeat, or severe injection site pain, burning, redness, or irritation (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for healthcare professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience and judgment in diagnosing, treating and advising patients.

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