Metered dose inhalers with spacers are devices capable of providing higher rates of lung
deposition of drugs such as beta agonists when compared to conventional nebulizers, but there
is no consensus about the optimal dose when this is the device of choice and there is
evidence that younger children need proportionally higher doses of albuterol (in μg/kg) when
compared to older children. Other factors that may interfere with response to albuterol
treatment include the genetics of the beta adrenergic receptor (ADRβ2) and infectious
etiology of the wheezing attack. This study will assess the effectiveness of a dose regimen
that prioritizes higher doses of albuterol, with doses in μg/kg higher for younger children.
Security of this new dosing regimen will be assessed by monitoring clinical side effects and
serum levels of albuterol, but the investigators will also examine the presence of 12
different respiratory viruses in these patients and evaluate the influence of ADRβ2 receptor
genetics in the response to albuterol. The primary outcome measure will be the need for
hospitalization. Secondary outcomes will include a change in clinical score, respiratory rate
and forced expiratory volume in the first second, the need for additional treatments and
length of stay in the emergency room for those not hospitalized.