isoproterenol
Isuprel

isoproterenol hydrochloride
Isuprel, Isuprel Mistometer

isoproterenol sulfate
Medihaler-Iso

Available forms
Available by prescription only
isoproterenol
Nebulizer inhaler: 0.25%, 0.5%, 1%
isoproterenol hydrochloride
Aerosol inhaler: 103 mcg/metered spray
Injection: 20 mcg/ml, 200 mcg/ml
isoproterenol sulfate
Aerosol inhaler: 80 mcg/metered spray

Indications and dosages
 Complete heart block after closure of ventricular septal defect. Adults: I.V. bolus, 0.02 to 0.06 mg (1 to 3 ml of a 1:50,000 dilution).
Children: I.V. bolus, 0.01 to 0.03 mg (0.5 to 1.5 ml of a 1:50,000 dilution).
 Bronchospasm during mild acute asthma attacks.
isoproterenol hydrochloride. Adults and children: Via aerosol inhalation, one inhalation initially, repeated, p.r.n., after 1 to 5 minutes, to maximum six inhalations daily. Maintenance dosage is one to two inhalations four to six times daily at 3- to 4-hour intervals. Via hand-bulb nebulizer, 5 to 15 deep inhalations of a 0.5% solution; if needed, may be repeated in 5 to 10 minutes. May be repeated up to five times daily.
 Or, three to seven deep inhalations of a 1% solution, repeated once in 5 to 10 minutes if needed. May be repeated up to five times daily.
isoproterenol sulfate.
Adults and children: For acute dyspneic episodes, one inhalation initially; repeated if needed after 2 to 5 minutes. Maximum six inhalations daily. Maintenance dosage is one to two inhalations up to six times daily.
 Bronchospasm in COPD. isoproterenol hydrochloride. Adults and children: Via hand-bulb nebulizer: 5 to 15 deep inhalations of a 0.5% solution, or 3 to 7 deep inhalations of a 1% solution no more frequently than q 3 to 4 hours.
 Bronchospasm during mild acute asthma attacks or in COPD. isoproterenol hydrochloride. Adults and children: Oral inhalation of 2 ml of 0.125% solution or 2.5 ml of 0.1% solution up to five times daily.
 Acute asthma attacks unresponsive to inhalation therapy or control of bronchospasm during anesthesia. isoproterenol hydrochloride. Adults: 0.01 to 0.02 mg (0.5 to 1 ml of a 1:50,000 dilution) I.V. Repeat, if needed.
 Emergency treatment of arrhythmias. isoproterenol hydrochloride Adults: Initially, 0.02 to 0.06 mg I.V. bolus. Subsequent dose 0.01 to 0.02 mg I.V. Or, 5 mcg/minute titrated to patient’s response. Range is 2 to 20 mcg/minute. Or, 0.2 mg I.M. or S.C.; subsequent doses 0.02 to 1 mg I.M. or 0.15 to 0.2 mg S.C. In extreme cases, 0.02 mg (0.1 of 1:5,000) intracardiac injection.
Children: May give half of initial adult dose.
 Immediate temporary control of atropine-resistant hemodynamically significant bradycardia. isoproterenol hydrochloride. Adults: 2 to 10 mcg/minute I.V. infusion, titrated to patient’s response.
Children: 0.1 mcg/kg/minute, titrated to patient’s response. Maximum rate is 1 mcg/kg/minute.
 Heart block, Stokes-Adams attacks, and shock. isoproterenol hydrochloride. Adults and children: 0.5 to 5 mcg/minute by continuous I.V infusion titrated to patient’s response; or 0.02 to 0.06 mg I.V. boluses with 0.01 to 0.2 mg additional doses; or 0.2 mg I.M. or S.C. with 0.02 to 1 mg I.M. or 0.15 to 0.2 mg additional doses.
 Postoperative cardiac patients with bradycardia ◇. Children: I.V infusion of 0.029 mcg/kg/minute.
 As an aid in diagnosing etiology of mitral regurgitation ◇. Adults: I.V. infusion of 4 mcg/minute.
 As an aid in diagnosing coronary artery disease or lesions ◇. Adults: I.V. infusion of 1 to 3 mcg/minute.

Pharmacodynamics
Bronchodilator action: Isoproterenol relaxes bronchial smooth muscle by direct action on beta₂-adrenergic receptors, relieving bronchospasm, increasing vital capacity, decreasing residual volume in lungs, and facilitating passage of pulmonary secretions. It also produces relaxation of GI and uterine smooth muscle via stimulation of beta₂ receptors. Peripheral vasodilation, cardiac stimulation, and relaxation of bronchial smooth muscle are the main therapeutic effects.
Cardiac stimulant action: Isoproterenol acts on beta₁-adrenergic receptors in the heart, producing a positive chronotropic and inotropic effect; it usually increases cardiac output. In patients with AV block, isoproterenol shortens conduction time and the refractory period of the AV node and increases the rate and strength of ventricular contraction.

Pharmacokinetics
Absorption: After injection or oral inhalation, absorption is rapid; after S.L. or rectal administration, absorption is variable and often unreliable.
Distribution: Distributed widely throughout the body.
Metabolism: Metabolized by conjugation in the GI tract and by enzymatic reduction in liver, lungs, and other tissues.
Excretion: Excreted primarily in urine as unchanged drug and its metabolites.

Contraindications and precautions
Contraindicated in patients with tachycardia caused by digitalis intoxication, in patients with arrhythmias (other than those that may respond to treatment with isoproterenol), and in those with angina pectoris. Use cautiously in the elderly and in patients with impaired renal function, CV disease, coronary insufficiency, diabetes, hyperthyroidism, or a sensitivity to sympathomimetic amines.

Interactions
Drug-drug. Beta blockers: Antagonize cardiac-stimulating, bronchodilating, and vasodilating effects of isoproterenol. Monitor patient closely.
Cardiac glycosides, potassium-depleting drugs, and other drugs that affect cardiac rhythm: Arrhythmias may occur. Monitor patient’s ECG.
Cyclopropane or halogenated hydrocarbon general anesthetics: Increases risk of arrhythmias. Avoid use together.
Epinephrine, other sympathomimetics: May cause additive CV reactions. Drugs may be used together if at least 4 hours elapse between administration of the two drugs. Use together cautiously.
Ergot alkaloids: May increase blood pressure. Use cautiously.

Adverse reactions
CNS: headache, mild tremor, weakness, dizziness, nervousness, insomnia.
CV: palpitations, tachycardia, anginal pain, arrhythmias, cardiac arrest,rapid increase and decrease in blood pressure, Stokes-Adams attacks.
GI: nausea, vomiting, heartburn.
Metabolic: hyperglycemia.
Respiratory: bronchospasm, bronchitis, sputum increase, pulmonary edema.
Skin: diaphoresis.
Other: swelling of parotid glands.

Effects on lab test results
• May increase glucose levels.

Overdose and treatment
Signs and symptoms of overdose include exaggeration of common adverse reactions, particularly arrhythmias, extreme tremors, nausea, vomiting, and profound hypotension.
 Treatment includes symptomatic and supportive measures. Monitor vital signs closely. Sedatives (barbiturates) may be used to treat CNS stimulation. Use cardioselective beta blockers to treat tachycardia and arrhythmias. Use these agents cautiously; they may induce asthmatic attack.

Special considerations
• Drug doesn’t replace administration of blood, plasma, fluids, or electrolytes in patients with blood volume depletion.
• Severe paradoxical airway resistance may follow oral inhalations.
• Hypotension must be corrected before isoproterenol is administered.
• Prescribed I.V. infusion rate should include specific guidelines for regulating flow or terminating infusion in relation to heart rate, premature beats, ECG changes, precordial distress, blood pressure, and urine flow. Because of danger of precipitating arrhythmias, infusion is usually decreased or temporarily discontinued if heart rate exceeds 110 beats/minute.
• Isoproterenol also has been used to aid diagnosis of coronary artery disease and mitral regurgitation.
• Isoproterenol may reduce the sensitivity of spirometry in the diagnosis of asthma.
• Carefully monitor response to therapy by frequent determinations of heart rate, ECG pattern, blood pressure, and central venous pressure, as well as (for patients in shock) urine volume, blood pH, and Pco₂ levels.
• Monitor patient for rebound bronchospasm when effects of drug end.
• Continuously monitor ECG during I.V. administration.
• If three to five treatments within 6 to 12 hours provide minimal or no relief, reevaluate therapy.
Pregnant patients
• Administer drug during pregnancy only when clearly indicated.
Breast-feeding patients
• It isn’t known whether drug appears in breast milk. Use cautiously in breast-feeding women.
Pediatric patients
• Use cautiously in children.
Geriatric patients
• These patients may be more sensitive to therapeutic and adverse effects of drug.

Patient education
• Urge patient to call if condition persists or worsens.
• Advise patient to store oral forms away from heat and light (not in bathroom medicine cabinet, where heat and moisture will cause deterioration of the drug). Keep drug out of the reach of children.
• Give patient instructions on proper use of inhaler.
• Tell patient that saliva and sputum may appear red or pink after oral inhalation because isoproterenol turns red on exposure to air.
• Advise patient to rinse mouth with water after drug is absorbed completely and between doses.
• Tell patient to allow S.L. tablet to dissolve under tongue, without sucking, and not to swallow saliva (may cause epigastric pain) until drug has been absorbed completely.
• Warn patient that frequent use of S.L. tablets may damage teeth because of acidity of drug.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use