Circulatory effects of oral and subcutaneous administration in normal subjects of a new bronchodilator, ibuterol, a pro-drug to terbutaline.

1 The di-isobutyryl ester of terbutaline, ibuterol, was given subcutaneously and orally to healthy volunteers and its effects on heart rate, arterial blood pressure, and ECG were compared with those of terbutaline itself. The effects of the two substances were qualitatively identical, but quantitatively different. 2 By mouth, ibuterol acted more rapidly, and was 2-3 times more active. After intramuscular injection, ibuterol caused less increase in local blood flow than terbutaline. 3 Ibuterol can be regarded as a pro-drug, which in itself has little activity, but which can be made active in the body.