Slow-responders to IV beta2-adrenergic agonist therapy: defining a novel phenotype in pediatric asthma

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.

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.

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.

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.