ImportanceStrategies to reduce medication dosing errors are crucial for improving outcomes. The Medication Education for Dosing Safety (MEDS) intervention, consisting of a simplified handout, dosing syringe, dose demonstration and teach-back, was shown to be effective in the emergency department (ED), but optimal intervention strategies to move it into clinical practice remain to be described.ObjectiveTo describe implementation of MEDS in routine clinical practice and associated outcomes.Design, Setting, and ParticipantsThis mixed-methods interrupted time series study of MEDS was conducted April 2021 to December 2022 in an academic pediatric ED using a hybrid type 1 design. Parents and guardians of children aged 90 days to 11.9 years who were discharged with acetaminophen, ibuprofen, or both were eligible for inclusion in the quantitative portion. Clinicians from a diversity of role groups (attending physician, resident, and nurse) were eligible for the qualitative portion.ExposuresThe study was conducted in 5 stages (baseline, intervention 1, washout, intervention 2, and sustainability phases). The 2 intervention phases taught clinical staff the MEDS intervention using different implementation strategies. During the intervention 1 phase, in-depth interviews were conducted until thematic saturation was reached; results were analyzed using thematic analysis. Interviews informed intervention 2 phase interventions.Main Outcomes and MeasuresThe primary outcome was any error (defined as dosing or frequency error) at a 48- to 72-hour follow-up phone call.ResultsThere were 256 participants (median [IQR] child age, 1.7 [3.0-7.0] years; median [IQR] parent and guardian age, 36.0 [31.0-41.0] years; 200 females among parents and guardians [78.1%]) who consented and completed follow-up. At baseline, 44 of 68 participants (64.7%) made an error compared with 34 of 65 participants (52.3%) during intervention 1, 31 of 63 participants (49.X%) during intervention 2, and 34 of 60 participants (57.X%) during sustainability. After adjustment for language and health literacy, the adjusted odds ratio for error during the combined intervention phases was 0.52 (95% CI, 0.28-0.97) compared with baseline.Conclusions and RelevanceThis study found that both MEDS intervention phases were associated with decreased risk of error and that some improvement was sustained without active intervention. These findings suggest that attempts to develop simplified, brief interventions may be associated with improved medication safety for children after discharge from the ED.