Racial differences in drug response: isoproterenol effects before and after propranolol.

The aim of this study was to determine in young, healthy men the relative contribution of pharmacodynamic factors inherent between two groups known to respond differently to hypertensive therapy. Black (n = 10) and white (n = 10) men received an isoproterenol sensitivity test before and after propranolol (0.1 mg/kg, then 50 micrograms/min). There were greater increases (twofold) in systolic BP following the 1.0- and 1.5-microgram isoproterenol dose (P less than 0.05) in the black group. During propranolol there were no differences in free (1)-propranolol concentrations between the groups; however, propranolol decreased resting heart rate in the white group more than in the black group (P less than 0.05). Cardiac index decreased less in the black group compared to the white group (P less than 0.05). Following the second isoproterenol challenge, there again were greater increases in systolic BP in the black group at both the 10- and the 20-micrograms isoproterenol dose (P less than 0.05). Our study has highlighted the importance of cross-racial studies in evaluating drug effects.