Double-blind comparison of acute bronchial and cardiovascular effects of oral terbutaline and ephedrine.

Acute effects of oral terbutaline (5 mg), ephedrine (25 mg) and placebo on bronchial dynamics, heart rate, systolic and diastolic pressure and arterial blood gases at rest were compared over a period of 7 hours in 20 subjects with bronchial asthma using a double-blind crossover technique. Both terbutaline and ephedrine caused significant bronchodilation, but the effect of terbutaline on specific airway conductance (SGA) was significantly greater (peak mean increase in SGA 0.069 vs 0.027 L/sec/cm H2O/L), had an earlier onset (30 minutes vs 1 hour) and lasted longer (7 hours vs 4 hours) than that of ephedrine. Slight but significant increases in arterial Po2 were noted following institution of both ephedrine and terbutaline, suggesting improvement in ventilation-perfusion relationships. Both drugs caused modest but statistically significant increases in heart rate of 8.4-10.9 beats/min and the mean peak increase following terbutaline (8.4 beats/min) was comparable to that following ephedrine. In constrast to ephedrine, terbutaline caused significant, although slight, increases in systolic pressure and decreases in diastolic pressure, indicating that this drug, in the dose recommended for clinical use, is not free of cardiovascular effects.