Dose-response study of a new oral bronchodilator, NAB 365 (clenbuterol).

A new oral bronchodilator, NAB 365 (clenbuterol), at doses of 10, 20, 30 and 40 microgram, was studied in a double-blind placebo-controlled incomplete cross-over study in 10 patients suffering from chronic bronchitis who had reversible airway obstruction. The ventilatory response was assessed by measurement of the forced expiratory volume in 1 sec (FEV1), total airway resistance (Raw) and specific airway conductance (sGaw) before and 30, 60, 120, 180, 240, 360 and 480 min after administration. With the 30 and 40 microgram doses, a significant bronchodilating effect was seen between 30 and 360 min after administration, with peak effects between 120 and 240 min. The maximal effects in ventilatory response after 30 microg were only slightly less than after 40 microgram; the bronchodilating effect of 20 microgram was statistically less marked than those of 30 of 30 and 40 microgram on FEV1, but not statistically different on Raw and sGaw. These findings have been briefly discussed. The effects of 10 microgram and of the placebo were always statistically lower than those of 20 microgram. No significant cardiovascular effects and no subjective side effects were observed. In conclusion, the results suggest that 30 microgram of NAB 365 (clenbuterol) are the suitable acute dose.