Slow-responders to IV β2-adrenergic agonist therapy:: Defining a novel phenotype in pediatric asthma

Objectives: While aerosolized administration of beta(2)-adrenergic receptor beta(2)-AR) agonists is the mainstay of treatment for pediatric asthma exacerbations, the efficacy of intravenous (IV) delivery is controversial. Failure to demonstrate improved outcomes with IV beta(2)-AR agonists may be due to phenotypic differences within this patient population. Our hypothesis is that children who respond more slowly to IV beta(2)-AR agonist therapy comprise a distinct phenotype. Methods: Retrospective chart review of all children admitted to the ICU for status asthmaticus who were treated with IV terbutaline between December 2002 and September 2006. Results: Seventy-eight children were treated with IV terbutaline according to guidelines that adjusted the dose by clinical asthma score. After examining the histogram of duration of terbutaline infusions, a 48-hr cutoff was chosen to define responsiveness. Thirty-eight (49%) children were slow-responders by this definition. There were no significant differences in baseline asthma severity or severity on admission between the slow-responders and responders. Slow-responders required significantly higher total doses of IV terbutaline, higher maximum administration rates, and had longer ICU and hospital length of stay. Conclusion: There were significant differences in outcomes between the responders and slow-responders without differences in acute or chronic illness severity Other factors may have lead to slower response to IV beta(2)-agonist therapy.