Duo-Medihaler

Generic name: isoproterenol hydrochloride and phenylephrine bitartrate
Dosage form: aerosol, metered
Drug class:Bronchodilator combinations

Medically reviewed by Drugs.com. Last updated on Sep 21, 2021.

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:

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 ...