Purpose:Omeprazole is a proton pump inhibitor (PPI) used in the treatment of gastrointestinal conditions, such as gastrointestinal esophageal reflux disease (GERD). Omeprazole is often prepared as an oral suspension to accommodate certain patients. Historically, oral suspensions of omeprazole were prepared using pharmaceutical compounding with sodium bicarbonate, but a kit for preparation of omeprazole oral suspension is available, FIRST® - Omeprazole. The purpose of this project is to compare the stability of the active pharmaceutical ingredient (API), omeprazole, in the FIRST® kit product to a traditionally compounded omeprazole suspension, when stored in refrigerated unit-dosed syringes. Methods: Five 100-mL batches of compounded omeprazole oral suspension (2 mg/mL) and five 300-mL kits of FIRST® - Omeprazole were prepared by a licensed pharmacist, and aliquoted into 5-mL doses in clear luer-lock plastic oral syringes, and stored at refrigerated temperature (2-8oC). Omeprazole concentration was assessed in each batch/kit on the day of preparation. Triplicate syringes from each batch/kit (n = 15 per test group per day) were removed after 7 days, 14 days, 21 days, and 30 days of refrigerated storage. Samples were diluted to assay concentration (1 mg/mL) in ion-free water and filtered using a 0.22-micron microcentrifuge filter tube. Samples were analyzed for omeprazole recovery using a validated high-performance liquid chromatography with ultraviolet detection (HPLC-UV) method. Recovery was quantitatively assessed by comparing sample peak area to a freshly prepared calibration curve (1 – 0.125 mg/mL) using United States Pharmacopoeia (USP) reference standard on each day of sampling. Refrigerator temperatures were recorded daily using a digital thermometer. Results:Stability was defined as recovery of 90 - 110% of initial concentration of API. For the FIRST® - Omeprazole samples, the chemical potency remained within this window for the entire study period of 30 days. The compounded omeprazole suspension demonstrated a less than 90% average recovery at the day 21 sample. Furthermore, a statistically significant difference in the initial concentration was detected on the day of compounding (p = 0.0244), with the compounded omeprazole starting at 1.89 ± 0.10 mg/mL and the FIRST® - Omeprazole at 1.98 ± 0.04 mg/mL. After 30 days, the compounded omeprazole suspension had an 89.13% average API recovery (standard deviation; ± 5.17%) and the FIRST® - Omeprazole 97.20% API recovery (± 3.59%). Conclusion:Both traditionally compounded omeprazole suspension (2mg/mL) and FIRST® - Omeprazole suspension (2mg/mL) may be stored in clear luer-lock oral syringes under refrigeration for 14 days, and retain potency between 90 to 110% based on initial concentration. Furthermore, the FIRST® - Omeprazole suspension can be stored for the duration of the product’s beyond-use date of 30 days and retain potency between 90 to 110% of initial concentration or label claim. Finally, the data suggest that API concentration in FIRST® - Omeprazole suspension is more consistent from batch to batch than traditionally compounded omeprazole suspension.