Background: It has been suggested that overuse of fenoterol metered-dose inhalers (MDIs) may increase the risk of death from asthma due to cardiac arrhythmias. Our primary objective was to compare the cardiovascular safety of fenoterol and albuterol MDIs when administered in maximal bronchodilating or maximal tolerated doses to an absolute maximum of 16 puffs, for the emergency department (ED) treatment of acute severe asthma.
Methods: Asthmatic patients presenting to the ED with acute severe asthma [FEV.sub.1] less than 50% of predicted) were enrolled in a multicenter, randomized, double-blind, parallel-group study. Following baseline measurements, (medical history, physical examination, determination of serum potassium and serum theophylline levels, oximetry, 12-lead ECG, and spirometry), each patient received 4 puffs of either fenoterol, 200 [mirco]g per puff, or albuterol, 100 [mu]g per puff, 1 puff every 30 s via an MDI attached to a holding chamber. Additional doses of inhaled
[[beta].sub.2]-agonist were administered by dose titration, 2 puffs every 10 min to a maximal cumulative dose of 16 puffs of albuterol or fenoterol, side effects were intolerable to the patient, or an [FEV.sub.1] plateau (ie, < 10% improvement for 2 consecutive doses) occurred. ECG was recorded continuously via Holter monitor, and respiratory rate, BP, dyspnea (Borg scale), and [FEV.sub.1] were assessed after each dose.
Results: 128 patients were randomized to receive fenoterol and 129 to receive albuterol. Overall, fenoterol increased [FEV.sub.1] 160 mL more than albuterol. The mean (SEM) [FEV.sub.1] increase from baseline was 0.75[+ or -]0.06 L in the fenoterol group and 0.59[+ or -]0.06 L in the albuterol group (p<0.03). Both [[beta].sub.2]-agonists caused a decrease in serum potassium level that was significantly greater in the fenoterol (0.23[+ or -]0.04 mmol/L) than in the salbutamol (0.06[+ or -]0.03 mmol/L) group (p=0.0002). There was also a greater increase in the Q-Tc interval in the fenoterol group, 0.011[+ or -]0.003 s compared with 0.003[+ or -]0.003 s in the albuterol group (p<0.05). Differences in hypokalemia and Q-Tc prolongation associated with fenoterol and albuterol were significantly different only after 8 puffs of fenoterol had been given. 32 patients exhibited ventricular premature beats, 14 in the fenoterol group and 18 in the albuterol group. There were 34 patients with episodes of supraventricular premature beats, 17 in each group. No episodes of sustained ventricular tachyeardia were detected in either group.
Conclusions: In adequately oxygenated patients, using dose titration of fenoterol, in a formulation of 200 [mu]g per puff by MDI valved holding chamber and mask, to a total dose of 3,200 [mu]g and salbutamol (100 [mu]g per puff) to a total dose of 1,600 [mu]g over 90 min, showed cardiovascular safety in acute severe asthma. This was evidenced by absence of cardiovascular mortality or clinically significant arrhythmias in either group. The 100% greater dose of fenoterol improved [FEV.sub.1] significantly more than salbutamol and was associated with a relatively small but significantly greater prolongation of the Q-Tc interval and decrease in serum potassium level. This study does not exclude the possibility that adverse cardiac events could occur with severe hypoxemia....