Bronchodilator intake and plasma levels on admission for severe acute asthma

We have measured the plasma levels of salbutamol, terbutaline and theophylline in 140 patients (70 men, mean age 57 yrs) arriving for emergency treatment with severe acute asthma. The aim of the study was to investigate how the measured plasma levels correlated with the reported bronchodilator intake and whether the pretreatment beta 2-agonist levels influenced the effect of emergency salbutamol treatment. We found a highly significant correlation between the reported 24 h dose and the measured plasma concentrations for all three drugs. A plasma concentration less than 40 mumol.l-1 was found in 63 of the 107 patients who had taken theophylline, while no patient had a plasma concentration greater than 110 mumol.l-1. A plasma concentration above the suggested therapeutic range was found in 23 of the 95 patients who had taken terbutaline (greater than 30 nmol.l-1) and in 12 of the 98 patients who had taken salbutamol (greater than 60 nmol.l-1). A significant negative correlation was found between the initial plasma beta 2-agonist levels and the bronchodilation after i.v. salbutamol treatment (5 micrograms.kg-1), while there was no clear indication that high plasma beta 2-agonist levels reduced the bronchodilator effect of a high dose of inhaled salbutamol (0.15 mg.kg-1 x 2). We conclude that some patients arriving with acute asthma have high blood concentrations of beta 2-agonists, which possibly limit the response to i.v. beta 2-agonist treatment, while the effect of high-dose inhaled beta 2-agonists appears to be related to a lesser degree to the drug concentration on arrival. In this study overtreatment with theophylline appears to be uncommon.