The use of β 2 -adrenoreceptor agonists in viral bronchiolitis: scientific rationale beyond evidence-based guidelines.

Despite scientific evidence proving that inhaled β2 -adrenergic receptor (β2 -AR) agonists can reverse bronchoconstriction in all ages, current guidelines advocate against the use of β2 -AR bronchodilators in infants with viral bronchiolitis because clinical trials have not demonstrated an overall clinical benefit. However, there are many different types of viral bronchiolitis, with variations occurring at an individual and viral level. To discard a potentially helpful treatment from all children regardless of their clinical features may be unwarranted. Unfortunately, the clinical criteria to identify the infants that may benefit from bronchodilators from those who do not are not clear. Thus, we summarised the current understanding of the individual factors that may help clinicians determine the highest probability of response to β2 -AR bronchodilators during viral bronchiolitis, based on the individual immunobiology, viral pathogen, host factors and clinical presentation.