New approach to assessment of cardioselectivity of beta-blocking drugs

Propranolol, practolol, and placebo were each given intravenously at weekly intervals to six normal subjects, and their effects on respiratory function tests and heart rates assessed. The reduction in the exercise heart rate after each of the two drugs was most comparable at six hours, indicating a similar degree of cardiac beta-blockade, when the plasma concentration ratio of practolol to propranolol was 28:1. The peak flow rate (PFR) was higher at all times during exercise than at rest. There were significant differences between the changes in resting and exercise PFR after placebo and the reductions after propranolol (except at 24 hours), but not after practolol-and the latter's influence on PFR seemed to be intermediate to that of propranolol and placebo. At six hours, when the cardiac beta-blocking activity of the two drugs was almost the same, there was a significant difference (P 0.025) between the reductions in exercise PFR associated with each drug.