Response to Inhaled Metaproterenol and Isoproterenol in Asthmatic and Normal Subjects

Pulmonary function tests were performed before and after inhalation of 1.3 mg of metaproterenol sulfate or 150μg of isoproterenol hydrochloride by 40 asthmatic and 40 normal subjects. Physiologic measurements included spirometric testing, plethysmographic studies, and maximal expiratory flow-volume curves obtained after inhalation of air and a mixture of 80 percent helium and 20 percent oxygen. In the normal subjects, pulmonary function improved significantly after inhalation of both metaproterenol and isoproterenol. There was no significant difference in responsiveness to either bronchodilator drug. In the asthmatic subjects, pulmonary function also improved significantly after both bronchodilator agents. The sites of predominant bronchodilatation were similar in the asthmatic subjects after both metaproterenol and isoproterenol; however, bronchodilatation was better overall (P < 0.005) and for most individual tests with metaproterenol. The greater efficacy of metaproterenol in asthmatic subjects but not in normal subjects can be explained by (1) different doses of the bronchodilator drug and (2) differing bronchodilator dose-response relationships in asthmatic and normal subjects.