Metaproterenol (Metaproterenol Sulfate Inhalation) - Description and Clinical Pharmacology

PRESCRIBING INFORMATION

FOR INHALATION USE ONLY–NOT FOR INJECTION.

DESCRIPTION

Metaproterenol Sulfate Inhalation Solution USP is a unit-dose bronchodilator administered by oral inhalation with the aid of an intermittent positive pressure breathing apparatus (IPPB). It contains 0.4% or 0.6% metaproterenol sulfate in a sterile, acidic, aqueous solution containing edetate disodium, sodium chloride, hydrochloric acid and/or sodium hydroxide for pH adjustment.

Chemical, metraproterenol sulfate is 3,5 dihydroxy-α-[(isopropylamino)methyl] benzyl alcohol sulfate (2:1), a white crystalline, racemic mixture of two optically active isomers. It differs from isoproterenol hydrochloride by having two hydroxyl groups attached at the meta positions on the benzene ring rather than one at the meta and one at the para position.

                                                                                                  (C₁₁H₁₇NO₃)₂•H₂SO₄
                                                                                                  M.W. 520.59

Metaproterenol Sulfate

CLINICAL PHARMACOLOGY

Metaproterenol Sulfate is a potent beta-adrenergic stimulator with a rapid onset of action. It is postulated that beta-adrenergic stimulants produce many of their pharmacological effects by activation of adenyl cyclase, the enzyme which catalyzes the conversion of adrenosine triphosphate to cyclic adenosine monosphosphate.

Absorption, biotransformation and excretion studies following administration by inhalation have not been performed. Following oral administration in humans, an average of 40% of the drug is absorbed; it is not metabolized by catechol-O-methyltransferase but is excreted primarily as glucuronic acid conjugates.

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 administered concurrently. The significance of these findings when applied to human usage is currently unknown.