Intravenous (IV) use of proton pump inhibitors (PPIs) is advised only in cases of suspected upper gastrointestinal bleeding (UGIB) or impossibility of receiving oral medication, although there has been a persistent practice of their inappropriate use in health institutions.The purpose of our study was to measure the inappropriate use of IV PPIs in a high complexity hospital in Brazil and to estimate its costs.Retrospective study of 333 patients who received IV omeprazole between July and December of 2018 in a high complexity hospital in Brazil.IV omeprazole was found to be appropriately prescribed in only 23.4% patient reports. This medication was administered mainly in cases of suspected UGIB (19.1%) and stress ulcer prophylaxis in patients with high risk of UGIB unable to receive medication orally (18.7%). It was observed a statistically significant association between adequate prescription and stress ulcer prophylaxis in patients with high risk of UGIB unable to receive medication orally; patient nil per os with valid indication for PPIs usage; prescription by intensive care unit doctors; prescription by emergency room doctors; intensive care unit admission; evolution to death; sepsis; and traumatic brain injury (P<0.05). On the other hand, inadequate prescription had a statistically significant association with surgical ward prescription and non-evolution to death (P<0.05). The estimated cost of the vials prescribed inadequately was US$1696.There was a high number of inappropriate IV omeprazole prescriptions in the studied hospital, entailing greater costs to the institution and unnecessary risks.