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OBJECTIVE To determine the dosing regimen of intravenous ranitidine (IVR) most likely to achieve a gastric pH of ≥4 in critically ill pediatric patients. METHODS A retrospective cohort study was designed and included patients younger than 19 years with gastric pH samples taken from a nasogastric tube within 24 hours after a dose of IVR in an intensive care unit. Data collection included patient demographics, clinical variables, IVR dosing, and gastric pH samples. Descriptive statistical analysis and multivariable logistic regression analysis with clustering of patients was performed to determine variables associated with odds of obtaining a pH of ≥4. RESULTS A total of 628 patients (1356 nasogastric samples) met study criteria (median age 1.3 years [IQR, 0.33, 5.7 years]; 53% male). The IVR dose was 0.90 ± 0.30 mg/kg per dose every 8.1 ± 2.9 hours, and 60.9% of patients (n = 383) had a pH ≥4. Patients with a pH value ≥4 had gastric pH samples taken earlier after a dose of IVR (6.7 ± 5.0 vs. 5.9 ± 4.7 hours, p < 0.001) but had no difference in IVR dose per kilogram (0.88 ± 0.31 vs. 0.88 ± 0.26, p = 0.86) or frequency of dosing (7.9 ± 3.2 vs. 7.9 ± 3.2 hours, p = 0.89). A multivariable logistic regression model identified increasing age, decreased kidney function, and decreased time to pH sample after an IVR dose with significantly greater odds of pH ≥4. CONCLUSIONS The IVR dosing to maintain a gastric pH ≥4 in critically ill pediatric patients should occur more frequently than every 8 hours. Gastric pH evaluation may be necessary to assess IVR efficacy.