Objective: To determine if early intervention with prednisolone in outpatients with bronchiolitis improves clinical illness scores, and if this improvement correlates with a reduction in Eosinophil Cationic Protein(ECP) levels.

Design: Randomized, double blind, placebo controlled trial.

Setting: Patients recruited from outpatient clinics associated with a tertiary care pediatric hospital and the Emergency Department at the same hospital.

Participants: Children 6 weeks to 15 months old with wheezing that started less than 48 hours prior to presentation. Exclusion critera included congenital heart disease, chronic lung disease, immunocompromise, prematurity of less than 34 weeks gestation and current age less than 6 months, and patients requiring immediate hospitalization.

Intervention: Patients were randomly assigned to receive prednisolone (N=12) 1 mg/kg twice a day for five days or placebo (N=13).

Outcome Measure: Change in clinical illness score and Eosinophil Cationic Protein level (ECP) from day 1 to day 2 (24 to 48 hours later).

Results: No significant change in clinical illness scores occurred between days 1 and 2 in either study group. Concentrations of ECP increased significantly (p=0.01) between days 1 and 2 in both controls (286 to 522 ng/ml) and prednisolone recipients (181 to 522 ng/ml). The increase in ECP occurred despite no significant change in severity of illness over the same interval.

Conclusions: Early intervention with prednisolone in outpatients with bronchiolitis did not affect clinical illness scores. ECP is unlikely to be involved in the pathogenesis of mild bronchiolitis, and may increase later in the inflammatory cascade of events after the disease has been established.