Klassen 1998.

Methods	Randomised double‐blind controlled trial
Participants	Study period: October 1995 to April 1996 and October 1996 to January 1997 Setting: emergency departments of the Children's Hospital of Eastern Ontario, Ottawa, or the Winnipeg Children's Hospital, Winnipeg, Canada Inclusion criteria: children aged 3 months to 5 years who presented to the emergency department with croup (hoarseness, inspiratory stridor, and barking cough) and Westley croup score of ≥ 2 following at least 15 minutes of mist therapy; parents available for telephone follow‐up a week after enrolling in the study Exclusion criteria: epiglottitis; chronic respiratory disease (except asthma); severe croup (Westley croup score ≥ 8); racemic epinephrine treatment upon arriving at the emergency department; glucocorticoids in the last 2 weeks; history of tuberculosis in child or household; chickenpox or exposure to it within the past 21 days; known immunodeficiency Baseline demographics (N = 198): proportion males: treatment 1: 77%; treatment 2: 62%; treatment 3: 64% median (25th, 75th percentile) age in years: treatment 1: 1.5 (1.0, 2.2); treatment 2: 1.3 (0.8, 2.1); treatment 3: 1.6 (1.0, 2.5) mean (95% CI) Westley croup score: treatment 1: 3.5 (3.2 to 3.7); treatment 2: 3.6 (3.3 to 3.8); treatment 3: 3.8 (3.5 to 4.0)
Interventions	Treatment 1 (N = 65): single 2 mg (4 mL) dose of nebulised budesonide plus the appropriate volume of oral placebo (clear syrup solution) Treatment 2 (N = 69): single 4 mL dose of nebulised placebo (saline solution) plus 0.6 mg/kg oral dexamethasone Treatment 3 (N = 64): single 4 mL dose of nebulised budesonide plus 0.6 mg/kg of oral dexamethasone
Outcomes	Change in Westley croup score from baseline to 4 hours (or until discharge); admissions to hospital; length of stay in the emergency department; 2‐point improvement in croup score at 4 hours; use of epinephrine and use of additional glucocorticoids
Notes	Funding source: Ontario Ministry of Health; Emergency Health Services, Toronto, Ontario; Manitoba Medical Services Foundation
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "A central pharmacy... randomized individuals to the 3 groups, using computer‐generated random numbers in random blocks of 6 or 9"
Allocation concealment (selection bias)	Low risk	Quote: "the list was kept at a central pharmacy until the end of the study to ensure allocation concealment. Because the drugs were packaged identically and identified only by a sequential study number, the research assistant who administered the intervention remained unaware of the next group assignment"
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "Dexamethasone syrup and placebo dexamethasone syrup were identical in taste and appearance... All solutions were packaged in brown syringes and the research assistant instilled either solution directly into an opaque nebulizer reservoir."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "Dexamethasone syrup and placebo dexamethasone syrup were identical in taste and appearance... All solutions were packaged in brown syringes and the research assistant instilled either solution directly into an opaque nebulizer reservoir."
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: intention‐to‐treat analysis used. 1% (N = 1) loss to follow‐up in the treatment group
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol identified. All prespecified outcomes from methods appear in results.
Other bias	Unclear risk	Comment: 10 children were not enrolled because the study team was not contacted; this could potentially have biased participant selection.
Overall risk of bias All outcomes	Unclear risk	Comment: at least 1 domain judged as unclear risk, and no domains judged as high risk.