Duo-Medihaler

DUO-MEDIHALER- isoproterenol hydrochloride and phenylephrine bitartrate aerosol, metered
3M Pharmaceuticals

Inhalation Aerosol

PHARMACIST: Tear off ‘Patient Instructions for Use” and dispense with product.

Description

DUO-MEDIHALER (isoproterenol hydrochloride and phenylephrine bitartrate) is a combination of two sympathomimetics administered by oral inhalation for the treatment of bronchoconstriction. Each metered dose of the aerosol delivers through the oral adapter 0.16 mg isoproterenol hydrochloride and 0.24 mg phenylephrine bitartrate of appropriate particle size (the majority less than 5 μ). This drug product also cortains cetylpyridinium chloride, dichloro­difluoromethane, dichlorotetrafluoroethane, sorbitan trioleate, and trichloromonofluoromethane. Chemically, isoproterenol hydrochlo­ride is 4-[1-hydroxy-2-[(1-methytethyl)amino]ethyl]-1,2-benzene­diol hydrochloride and phenylephrine bitartrate is (-)-m -hydroxy­-a -[(methylamino) methyl]benzyl alcohol bitartrate.

Structural formulae:

Image from Drug Label Content

Clinical Pharmacology

Isoproterenol acts directly on beta-adrenergic receptors and phenylephrine acts directly on alpha-adrenergic receptors. The beta-adrenergic effects stem from the release of cyclic AMP following activation of the enzyme adenyl cyclase. Alpha-adren­ergic effects probably result from inhibition of adenyl cyclase. Isoproterenol produces bronchodilatation, systemic vasodilation, mild hypotension, and tachycardia. Phenylephrine produces mild bronchodilatation, systemic vasoconstriction, mild hypertension, and bradycardia. These two drugs appear to act synergistically to allow the expression of each product’s ability to relax bronchial smooth muscle. The vasoconstrictor effect of phenylephrine reduces bronchiolar blood flow thereby producing a decongestant effect, promotes retention of the drug in the bronchial mucosa, and blocks the tachycardia of isoproterenol. After oral inhalation of the combination, the pulmonary effects occur within a few minutes and persist up to three hours.

Studies demonstrate that the ventilatory effects of isoproterenol­phenylephrine are superior to those obtained with the administration of isoproterenol alone. Because isoproterenol is a potent vasodilator that lowers blood pressure and acts upon the heart to increase cardiac output and pulse rate, its combination with phenylephrine results in a product with fewer cardiovascular effects. Studies have shown the absence of tachycardia and hypotension.

Isoproterenol alone often lowers arterial blood oxygen (PO2 ). Several studies have shown that the combination of isoproterenol and phenylephrine rarely produces a significant drop in arterial oxygen tension while usually producing an increase in Pa O2 in asthmatic patients.

Pharmacokinetics: The average half-life for isoproterenol admin­istered by aerosol was five minutes. A plasma concentration of 0.03 ng/ml was found within minutes following an inhalation dose of 500 mcg isoproterenol.

Isoproterenol excretion following oral or inhalation administration is primarily renal. When given by inhalation, the major metabolite is the sulfate conjugate of the drug. When the drug is administered directly into the bronchial tree, it is inactivated by the enzyme catechol-o -methyl transferase, and the predominant metabolite is 3-o -methylisoproterenol sulfate. The explanation for this difference is supported by the observation that most (90%) of an aerosol dose is deposited in the mouth, swallowed, and converted to its sulfate conjugate in the gut wall, and to a lesser extent in the liver. The remaining isoproterenol is excreted as follows: 1% to 2% unchanged, 1% to 2% free methylated metabolite, and small amounts of metabolites in the bile.

Plasma levels following inhalation of phenylephrine have not been reported. Following oral and intravenous administrations, the average half-life was about 2.5 hours. Phenylephrine is metabo­lized in the liver and intestine by the enzyme monoamine oxidase. About 80% of a dose is recovered in the urine, primarily as phenolic conjugates and m -hydroxymandelic acid. About 16% of a dose is excreted as unchanged drug following intravenous administration and, due to first pass metabolism, less than 3% is excreted unchanged following oral dosing.

Recent studies in laboratory animals (minipigs, rodents, and dogs) recorded the occurrence of cardiac arrhythmias and sudden death (with histologic evidence of myocardial necrosis) when beta agonists and methylxanthines were concomitantly administered. The significance of these findings when applied to human usage is currently unknown.

Indications And Usage

DUO-MEDIHALER is indicated for the treatment of bronchospasm associated with acute and chronic asthma and reversible broncho­spasm which may be associated with chronic bronchitis or emphysema.

Contraindications

DUO-MEDIHALER must not be used by patients with known hyper­sensitivity to sympathomimetics. The use of isoproterenol in patients with pre-existing cardiac arrhythmias associated with tachycardia is contraindicated because the cardiac stimulant effects of the drug may aggravate such disorders.

WARNINGS

Excessive use of an adrenergic aerosol should be discouraged, as it may lose effectiveness. Occasional patients have been reported to develop severe paradoxical airway resistance with repeated, excessive use of isoproterenol inhalation preparations (see ADVERSE REACTIONS). The cause of this is unknown. It is advis­able that in such instances the use of this preparation be discon­tinued immediately and alternative therapy instituted, since in the reported cases the patients did not respond to other forms of therapy until the drug was withdrawn. Deaths have been reported following excessive use of isoproterenol inhalation preparations, and the exact cause is unknown. Cardiac arrest was noted in several instances (see ADVERSE REACTIONS).

Precautions

General: As with all sympathomimetic drugs, DUO-MEDIHALER should be used with great caution in the presence of coronary insufficiency, hypertension, hyperthyroidism, and diabetes.

Information for Patients: Patients who are being treated with DUO­-MEDIHALER should be informed adequately of the dangers of overusage, tolerance and rebound bronchospasm (see WARNINGS and ADVERSE REACTIONS sections). They should be instructed to take no more than two inhalations at any one time, nor more than six in any one hour during a 24-hour period, unless advised by the physician (see DOSAGE AND ADMINISTRATION and Patient Instructions for Use sections).

Isoproterenol may cause the patient’s saliva to turn pinkish to red in color. Proper use of DUO-MEDIHALER oral inhaler should be demonstrated and discussed. Patient Instructions for Use are available with the package insert and should be provided when the medication is dispensed.

As with any drug, patients should be advised against the ingestion of alcohol during treatment.

Drug Interactions: A monoamine oxidase (MAO) inhibitor, a tricyclic antidepressant, or guanethidine may increase the cardiac and pressor effects of phenylephrine and isoproterenol; however, normal volunteers given isoproterenol by inhalation along with an MAO inhibitor or a tricyclic antidepressant had no adverse cardio­vascular effects.

Arrhythmias may result from the concurrent administration of isoproterenol or phenylephrine to patients who are receiving digitalis, epinephrine, cyclopropane, or halogenated hydrocarbon anesthetics.

Beta-adrenergic blocking drugs such as propranolol antagonize the cardiac, bronchodilating, and vasodilating effects of isoproterenol and the stimulating effects of phenylephrine.

Ergot alkaloids may increase blood pressure in patients receiving iso­proterenol or phenylephrine. Phentolamine mesylate (Regitine®), an alpha-adrenergic blocker, may decrease the pressor response to phenylephrine.

Phenothiazine drugs have some alpha-adrenergic blocking activity and may reduce the pressor effects and duration of action of phenylephrine.

Drug/Laboratory Test Interactions: Isoproterenol causes false elevations of bilirubin as measured in vitro by sequential multiple analyzer. An effect on serum bilirubin determinations in patients receiving the drug has not been determined. One case of surrepti­tious self-administration of a 500 mg subcutaneous dose of isopro­terenol resulted in increased urinary excretion of epinephrine, norepinephrine, and vanilmandelic acid. Isoproterenol inhalation may result in enough absorption of the drug to produce increased values for urinary epinephrine. This effect is probably small with standard doses, but is likely to increase with larger doses.

Carcinogencity, Mutagenesis, and Impairment of Fertility: Isoproterenol hydrochloride, phenylephrine bitartrate, or DUO-­MEDIHALER have not been evaluated for carcinogenicity, muta­genicity or impairment of fertility.

Pregnancy: Teratogenic Effects — Pregnancy Category C: Repro­duction studies have not been done with DUO-MEDIHALER or phenylephrine. Reproduction studies with isoproterenol have been performed in rats and rabbits with aerosol doses (30 minutes per day for 12 days) up to 15 times the human dose and have revealed no evidence of impaired fertility or harm to the fetus. It is also not known whether DUO-MEDIHALER can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. DUO-MEDIHALER should be given to a pregnant woman only if clearly needed.

Labor and Delivery: DUO-MEDIHALER has no recognized use during labor and delivery. Phenylephrine administration during late pregnancy or labor may cause fetal anoxia and bradycardia by increasing uterine contractility and decreasing uterine blood flow.

Nursing Mothers: It is not known whether isoproterenol or phenyl­ephrine is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when DUO­MEDIHALER is administered to a nursing woman.

Pediatric Use: Safe and effective use of DUO-MEDIHALER in children below the age of 12 has not been established.

Geriatric Use: Lower doses in elderly patients may be required due to increased sympathomimetic sensitivity (see DOSAGE AND ADMINISTRATION).

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