Effect of prenalterol in asthmatic patients

The bronchial effects of prenalterol, a selective inotropic beta-adrenoceptor agonist, were examined to see whether beta 1-adrenoceptor stimulation would produce bronchodilatation, or whether beta 2-adrenoceptor blockade could be demonstrated. In a first investigation 8 asthmatic patients were studied under standardized conditions in a double-blind, randomized, crossover comparison between i.v. doses of prenalterol and saline infusions. After the fourth dose of prenalterol/saline, 4 intravenous doses of terbutaline were given. All medication was given at 30 min intervals. In a second study in 7 of the previously studied patients, 5 increasing doses of prenalterol or saline were inhaled from a bird ventilator, and after the last dose 4 i.v. doses of terbutaline were given as before. Prenalterol and saline caused no change in FEV1 during the intravenous study. Terbutaline infusion produced a dose dependent increase in FEV1 which was not significantly altered after prenalterol treatment. In the inhalation study, in which a much larger dose was applied to the bronchial tree, there was no significant difference in FEV1, between the saline and prenalterol inhalations. However, prenalterol did show beta 2-blocking property, as the dose response curve of terbutaline was shifted to the right. The heart rate increased significantly and to the same degree during both the i.v. and inhaled prenalterol treatments. Thus, this study revealed no significant beta 2-blocking effect of therapeutic doses of i.v. prenalterol. However, when the drug was inhaled in a much higher dose, a beta 2-blocking effect on FEV1 was recorded. No significant beta 1-adrenoceptor-mediated bronchodilator effect of prenalterol could be demonstrated.