Plasma concentrations of salbutamol in acute severe asthmatics

We studied prospectively 11 asthmatic patients presenting to the Accident and Emergency department with acute asthma. (Four patients reported historically that they were taking some form of oral salbutamol as part of their maintenance therapy.) Standard cardiovascular and respiratory parameters and plasma salbutamol concentrations were measured before and one hour after treatment with five milligrams of nebulised salbutamol. The median plasma salbutamol concentration before treatment was below the level of detection of the assay (less than 3 ug.l^-1) with a range from less than 3 ug.l^-1 to 34.6 ug.l^-1. One hour post treatment the median plasma salbutamol concentration was 7.4 ug.l^-1 (range<3.0 ug.1^-1 to 56.0 ug.1^-1) p <0.05. (Wilcoxons test). Correlations were investigated between the measured pretreatment physiological variables and pre-treatment plasma salbutamol concentrations. None were found to be significant. Similar analysis of the measured post-treatment physiological variables and post-treatment plasma salbutamol concentrations again revealed no significant correlations. However, a significant negative correlation was noted between the change in plasma salbutamol concentration with treatment and the change in respiratory rate (Rs=–0.56, p= 0.04). If asthmatics do indeed use high doses of inhaled beta-2-agonists (salbutamol) in an attempt to abort an acute attack (as many clinicians suspect) little, if any, of the drug appears to reach the systemic circulation. In this study the administration of five milligrams of nebulised salbutamol to acute asthmatics did not produce excessive increases in plasma salbutamol concentration, even in those patients taking oral salbutamol as part of their maintenance therapy.