Wheezing is one of the most common reasons young children visit the emergency department (ED), and for years clinicians have debated whether azithromycin might help — particularly given that common bacteria are frequently found in the airways of these children. A large PECARN-led trial now provides a clear answer: it does not appear to help.
The AZ-SWED trial (Azithromycin Therapy in Preschoolers with a Severe Wheezing Episode Diagnosed at the Emergency Department), published in the New England Journal of Medicine, found no meaningful clinical benefit from a 5-day course of azithromycin compared with placebo in 840 preschool-aged children with moderate-to-severe wheezing [1].
Study Design
AZ-SWED was a multicenter randomized clinical trial conducted across eight pediatric emergency departments in the United States through the Pediatric Emergency Care Applied Research Network (PECARN).
Investigators enrolled 840 children between 18 and 59 months of age who presented to the ED with moderate-to-severe wheezing. Children were randomly assigned to receive either:
- Azithromycin for 5 days — an antibiotic commonly prescribed in respiratory illness
- Placebo for 5 days — an identical-appearing inactive treatment
All children also received standard therapies such as bronchodilators and corticosteroids as determined by their clinical care teams.
Because prior studies suggested certain bacteria might influence wheezing illnesses, researchers also evaluated whether outcomes differed in children with common airway bacteria such as:
- Streptococcus pneumoniae
- Moraxella catarrhalis
- Haemophilus influenzae
The primary outcome was symptom severity over 5 days, measured using the Asthma Flare-up Diary for Young Children (ADYC), a validated caregiver-reported score.
Results
Azithromycin provided no meaningful benefit.
ADYC symptom scores over 5 days were similar between the azithromycin and placebo groups — both in children with detectable airway bacteria and those without. There were no important differences in:
- Hospitalization rates
- Length of stay
- Return ED visits
- Clinical recovery
Respiratory viruses were extremely common in the study population, with rhinovirus identified in more than 70% of participants. The three pathogenic bacteria were detected in 62% of participants.
Although azithromycin increased bacterial clearance from the nasopharynx, this microbiologic effect did not translate into improved symptoms or better clinical outcomes.
The study was ultimately stopped early for futility after interim analyses demonstrated a very low likelihood that continued enrollment would show benefit.
Why This Matters
For years, clinicians have questioned whether azithromycin might help preschool children with wheezing, particularly because some smaller outpatient studies suggested potential benefit when antibiotics were started early in respiratory illnesses. AZ-SWED provides strong evidence that for children already sick enough to require emergency care, routine azithromycin treatment does not improve outcomes.
This is important for several reasons:
- It supports evidence-based stewardship of antibiotic use
- It helps reduce unnecessary antibiotic exposure
- It provides clinicians with clearer guidance in a very common pediatric ED presentation
The findings also suggest that the presence of common airway bacteria alone should not drive antibiotic decisions in preschool wheezing illnesses.
Take Home Message
For preschool children presenting to the ED with significant wheezing, azithromycin did not improve symptom severity, reduce hospital utilization, or speed recovery compared with placebo.
The most important aspects of care remain supportive management, bronchodilator therapy, corticosteroids when appropriate, and careful clinical assessment, not routine antibiotic use.
Why is this important for patients and caregivers
- Wheezing illnesses are very common in young children and are one of the leading reasons families seek emergency care.
- This study showed that adding azithromycin did not help children recover faster or avoid hospitalization compared with standard care alone.
- For families, this means clinicians can focus on treatments that are proven to help while avoiding unnecessary antibiotics and their potential side effects.
Interested in other PECARN research?
A few recent PECARN studies:
- Achievable Benchmarks of Care in Pediatric Emergency Departments — Alpern et al, JAMA Network Open, 2026. A study of over 5 million pediatric ED visits identifying realistic performance targets that top-performing hospitals achieve, with significant variation found in areas like pain management across sites. PMID: 42154467. doi:10.1001/jamanetworkopen.2026.13391
- Comparison of Cervical Spine Injury Prediction Rule Across Ages — Corwin et al, Pediatrics, 2026. A 22,000-patient multicenter study showing the PECARN cervical spine injury prediction rule performs consistently well across all pediatric age groups without requiring age-specific modifications. PMID: 42061904. doi:10.1542/peds.2025-075341
- Balanced Fluid or 0.9% Saline in Children Treated for Septic Shock: The PRoMPT BOLUS Trial — Balamuth et al, N Engl J Med, 2026. A landmark international trial showing both IV fluid types are equally safe and effective in children with septic shock. PMID: 42028918. doi:10.1056/NEJMoa2601969. Read more on PECARN.
References
- Denninghoff KR, Casper TC, Zorc JJ, et al. Azithromycin for Preschoolers with Wheezing in the Emergency Department. N Engl J Med. Published online May 18, 2026. PMID: 42149992. doi:10.1056/NEJMoa2516505
