<p><strong>OBJECTIVE: </strong>To examine the use, efficacy, and safety of intravenous magnesium sulfate (IVMg) in children with asthma whose emergency department (ED) management is recorded in the Pediatric Emergency Care Applied Research Network (PECARN) Registry.</p>

<p><strong>STUDY DESIGN: </strong>This multicenter retrospective cohort study analyzed clinical data from 7 EDs from 2012 to 2017. We described use of IVMg in children aged 2-17&nbsp;years treated for acute asthma and its effect on blood pressure. We also used multivariable analysis to examine factors associated with use of IVMg and its association with return visits within 72&nbsp;hours.</p>

<p><strong>RESULTS: </strong>Across 61 854 asthma visits for children, clinicians administered IVMg in 6497 (10.5%). Median time from triage to IVMg administration was 154&nbsp;minutes (IQR 84, 244). During 22 495 ED visits resulting in hospitalization after ED treatment, IVMg was administered in 5774 (25.7%) (range by site 15.9%, 50.6%). Patients were discharged home from the ED after 11.1% of IVMg administrations, and hypotension occurred after 6.8%. Variation in IVMg use was not explained by patient characteristics. Revisits did not differ between patients discharged after IVMg and those not receiving IVMg.</p>

<p><strong>CONCLUSIONS: </strong>In PECARN Registry EDs, administration of IVMg occurs late in ED treatment, for a minority of the children likely to benefit, with variation between sites, which suggests the current clinical role for IVMg in preventing hospitalization is limited. Discharge after IVMg administration is likely safe. Further research should prospectively assess the efficacy and safety of early IVMg administration.</p>