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A comparison of the haemodynamic and hypokalaemic effects of inhaled pirbuterol and salbutamol.

In this double blind study, the cardiovascular and hypokalaemic effects of equal doses of inhaled pirbuterol and salbutamol were compared in eight healthy volunteers. Increasing doses of 200, 400, 600 and 800 micrograms (total dose 2000 micrograms) were given from a metered dose inhaler at 15 min intervals, followed by measurement of heart rate, blood pressure, total electromechanical systole (QS2I) (as a measure of inotropic response) and plasma potassium (K+) concentration 15 min after each inhalation. After inhalation of the highest concentration, salbutamol resulted in a greater increase in heart rate (10.5 bpm vs 4.4 bpm, p less than 0.0007), and reduction in QS2I (-25.4 ms vs -9.6 ms, p less than 0.0001) than pirbuterol. There were no significant differences in changes in systolic blood pressure (1.9 mmHg vs 6 mmHg, p = 0.27), diastolic blood pressure (-5.8 mmHg vs -3.9 mmHg, p = 0.64) or plasma K+ (-0.21 mmol/L vs -0.15 mmol/L, p = 0.57). We conclude that the new beta-2 adrenergic agonist pirbuterol is at least as beta-2 selective as salbutamol when administered by repeated inhalation in healthy volunteers.