Comparison of the beta2‐adrenoceptor selectivity of rimiterol, salbutamol and isoprenaline by the intravenous route in man.

1 The bronchodilating efficacy and the degree of beta2‐adrenoceptor selectivity of rimiterol, salbutamol and isoprenaline were determined in seven subjects who exhibited histamine‐induced bronchoconstriction. 2 Rimiterol, 0.5 (high dose) and 0.05 (low dose) mug kg‐1 min‐1, salbutamol, 0.3 and 0.03 mug kg‐1 min‐1, isoprenaline, 0.05 and 0.005 mug kg‐1 min‐1 and placebo were administered by a single intravenous injection over 6 min, and the protection against histamine‐induced bronchoconstriction, changes in heart rate, pulse pressure and skeletal muscle tremor were measured. 3 Rimiterol (98%), salbutamol (96%) and isoprenaline (69%) protected against histamine‐induced bronchoconstriction. For these ventilatory responses, there was a heart rate increase of 31.9, 24.7 and 44.3 beats/min for rimiterol, salbutamol and isoprenaline respectively. The three drugs produced similar increases in pulse pressure and tremor. 4 Significant dose‐ responses were obtained for all the parameters with each drug. 5 Isoprenaline was approximately 7 and 5 times as potent as rimiterol and salbutamol respectively in bronchodilator action when equimolar doses were compared. Similarly, isoprenaline was approximately 14 and 10 times as potent in increasing the heart rate as rimiterol and salbutamol respectively. 6 Rimiterol, a new beta‐adrenoceptor stimulating drug, is an effective bronchodilator and has similar beta2‐ adrenoceptor selectivity to salbutamol when administered intravenously. The relative potencies and degrees of beta2‐adrenoceptor selectivity of these drugs depend partly on their route of administration.