Comparison of intravenous ibuterol (KWD 2058), a new bronchodilator, and terbutaline

The selectivity of the recently developed beta-stimulating drug ibuterol, a terbutaline ester which is rapidly hydrolyzed to terbutaline in vivo, was tested by comparing it with terbutaline after intravenous infusion. Dose-response curves for both drugs for FEV, heart rate, blood pressure, and tremor were recorded. The two drugs had equal bronchodilator effect. Ibuterol caused significantly less increase in heart rate, tremor ratio, and pulse amplitude when doses causing equal bronchodilation were infused. This is probably due to inequality of distribution. The lower tremorogenic activity of ibuterol can also be caused by differences in the concentration of tissue esterases in lung and skeletal muscle. It is concluded that ibuterol is more selective for the bronchi than terbutaline.