White or almost white, slightly hygroscopic, crystalline powder.
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Beta2-adrenoceptor agonist; bronchodilator.
Pharmacokinetics
Metaproterenol is a direct-acting resorcinol analogue of isoproterenol. The N-isopropyl is
β-directing, and the combination with the resorcinol ring system enhances the selectivity for the
β2-receptors. It is the least potent of the β2-selective agonists, however, most likely because of
the poor β2-selectivity of the isopropyl group. It has good oral bioavailability being resistant to
COMT and only slowly metabolized by MAO. When administered orally, it has an onset of
approximately 30 minutes with a 4-hour duration. Inhaled metaproterenol can have an onset as
quick as 5 minutes; however, it can be as long as 30 minutes in susceptible individuals.
Metaproterenol is available in tablet, syrup, and inhalation dosage forms and is recommended for
bronchial asthma attacks and treatment of acute asthmatic attacks in children 6 years of age and
older (5% solution for inhalation only). Metaproterenol has the same adverse effect profile as
other adrenergic agonists, but with a decreased incidence of arrhythmias.
