Abstract

Acute bronchiolitis is the leading cause of hospitalization in infants, with few pharmacological treatments of proven efficacy. Given that magnesium sulfate (MgSO4) has shown benefits in the management of asthma, it has been proposed as a potential adjuvant therapy; however, the evidence remains limited. Objective: To evaluate the effectiveness of MgSO4, compared with standard therapy with or without placebo, in reducing symptoms and length of hospital stay in infants with bronchiolitis. Methods: A systematic review of randomized clinical trials (RCTs) was conducted. Searches were performed using MEDLINE, EMBASE, SciELO, LILACS, clinical trial registries, grey literature, and bibliographic reviews (last search: December 2, 2025). Studies including infants under 24 months with acute bronchiolitis were selected. Risk of bias was assessed using the RoB2 tool. A meta-analysis was performed using a random-effects model. The primary outcome was clinical response (at 1 hour and 3-4 hours), and the secondary outcome was length of hospital stay. Results were synthesized using standardized mean differences (SMD) and mean differences (MD). Results: Four RCTs were included (n = 401). MgSO4 showed no significant differences compared with standard therapy in clinical improvement at 1 hour (SMD: 0.17 95%CI-0.23 to 0.57) or at 3-4 hours (SMD:-0.07 95%CI-0.32 to 0.19). Length of hospital stay also showed no significant differences (MD:-0.34 hours 95%CI-3.39 to 2.72). The certainty of the evidence was rated as low to moderate according to GRADE. Conclusions: Magnesium sulfate does not provide clinically significant benefits in reducing symptoms or length of hospital stay in acute bronchiolitis. According to the GRADE approach, there is a conditional recommendation against its routine use in infants with acute bronchiolitis, based on low to moderate certainty evidence.