Tolerance and beta-adrenergic blocking activity of flestolol, a short-acting beta blocker

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Abstract
The tolerance and .beta.-adrenergic blocking activity of flestolol, a short-acting .beta.-blocker, was investigated in 30 subjects. Flestolol infused intravenously at doses up to 100 .mu.g/kg/min was found to be well tolerated. A dose-dependent attenuation of isoproterenol-induced tachycardia and increase in systolic blood pressure occurred with flestolol at doses ranging from 0.5 to 15.0 .mu.g/kg/min. The average percent reduction in isoproterenol-induced tachycardia (.beta.-blockade) at each dose of flestolol, 0.5, 2.5, 5.0, 15.0, and 50.0 .mu.g/kg/min, was 15.1%, 45.9%, 67.0%, 85.9%, and 90.3%, respectively. The onset of .beta.-blockade occurred within 30 minutes. After the end of flestolol infusion there was a marked reduction in .beta.-blockade within 6 minutes, with complete recovery from .beta.-blockade within 30 to 45 minutes. There was a statistically significant (P < 0.01) positive correlation between flestolol dosage and its blood levels (r = 0.91) as well as between the flestolol-induced .beta.-blockade and its dosage (r = 0.62).