Racial differences in sensitivity to the negative chronotropic effects of propranolol in healthy men*

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Abstract
Objective Dose‐response studies in patients with hypertension have shown that black subjects are less responsive to β‐blocker therapy than white subjects, whereas studies in healthy volunteers suggest marginal or no racial differences in response. No concentration‐response studies have been conducted in black subjects and white subjects. The purpose of this study was to characterize β‐blocker pharmacodynamics in healthy black and white men. Methods Thirteen black and 13 white healthy men took 80 mg oral propranolo three times daily, for a total of 16 doses. Heart rate response to treadmill exercise was measured at various times over 24 hours. Serum propranolol samples were collected during the same 24‐hour time period and were measured by chiral HPLC. The sigmoid maximal effect (Emax), Emax, and linear models were fitted to percentage reductions in exercise heart rate and S‐propranolol concentrations. Results Black subjects had significantly lower values for serum concentration producing one‐half the maximal effect (EC50) and unbound EC50 than white subjects (EC50: 10.2 ng/ml (4.4 to 28.0 ng/ml) versus 24.4 ng/ml (14.3 to 64.1 ng/ml), blacks versus whites; unbound EC50: 1.29 ng/ml (0.686 to 4.91 ng/ml) versus 2.77 ng/ml (1.70 to 8.11 ng/ml), blacks versus whites). There was no statistical difference in Emax (33.3% [22.2% to 39.7%] versus 38.3% [30.7% to 45.1%], blacks versus whites). Conclusions Healthy black men were more sensitive to β‐blockade than healthy white men. The results of this study in healthy volunteers suggest that the racial differences in response observed in patients with hypertension are related to hypertensive pathophysiology rather than normal physiology. Clinical Pharmacology & Therapeutics (1995) 57, 678–683; doi: