Beta-blocker duration of action and implications for therapy. Two studies were conducted to measure the effect of serum half-life on beta-blocker-related heart rate reduction throughout the 24-hour period. In the first study, nadolol, atenolol and pindolol were associated with significant (p less than 0.01) heart rate reduction even at 24 hours after dose. Nadolol, with a plasma half-life of 15.5 hours, had the most pronounced heart rate-lowering effect 24 hours after the daily dose compared to pindolol, which had a half-life of 5.5 hours. In a randomized, double-blind, crossover study, nadolol and atenolol had similar effects 3 to 4 hours after the daily dose. Nadolol, however, produced greater suppression of heart rate and double product (blood pressure x heart rate) than atenolol (compared to placebo) 24 hours after ingestion of the daily dose. On ambulatory electrocardiography 24 hours after medication administration, 80 to 100% of the heart rate-attenuating effect of nadolol was maintained versus only 20 to 45% of atenolol's effect. Statistically significant (p less than 0.05) reductions in heart rate were produced by nadolol, but not by atenolol, between 4 and 5 A.M., 6 and 7 A.M., 8 and 9 A.M. and 9 and 10 A.M. Furthermore, nadolol remained at 52% of peak blood level at 24 hours, whereas atenolol was at 20%. The data from these 2 studies indicate that significant differences in duration of action exist between beta blockers. 