Introduction. The prevalence of the use of drugs that act on the gastric system has increased in the population. Omeprazole is an inhibitor of the protons pump and has a widespread use, mainly as a prophylactic to prevent reflux esophagitis, gastric pathological hypersecretory conditions, prevention of recurrence of gastric or duodenal ulcers, gastric mucosal protection against damage caused by nonsteroidal anti-inflammatory drugs and during Zollinger-Ellison syndrome. However, omeprazole is associated with several adverse events due to abusive use or irrational prescribing, in disagreement with the indication, which may cause the ineffectiveness of the drug and decreased patient safety. Objectives. To assess the risk (occurrence of adverse events) and the benefit (effectiveness) of the prophylactic use of omeprazole in hospitalized patients and to know the reasons for the prophylactic use (indicated use or not approved). Patients and Methods. A observational and cross pharmacoepidemiological study will be performed from June to November 2014, in the General State tertiary referral Américo Brasiliense Hospital. Hospitalized patients will be separated into three groups: those who make indicated and approved prophylactic use of omeprazole (exposed group 1), those who make not indicated and not approved prophylactic use (exposed group 2), and those who do not use the omeprazole (non-exposed group). Patients who do not make prophylactic use of omeprazole will be excluded. Patients will have their pharmacotherapy monitored and data will be collected daily using an investigation guide of the first day of admission and will be included in group 1 or 2, from the first use of omeprazole to discontinuation (washout period of seven half-lives or higher). National Coordinating Council for Medication Error Reporting and Prevention (NCCMERP) algorithm will be used for causality analysis is used. Data will be tabulated according to the presence or absence of effectiveness and the presence or absence adverse events in the three groups. The odds ratio of adverse events and effectiveness of indicated and approve or not indicated and not approved prophylactic use of omeprazole will be calculated. Expected results. It is intended to know the odds ratio of adverse events in the prophylactic use of omeprazole with or without indication or use approval, and the potential indications, dosage and unapproved methods of prophylactic use in omeprazole label.

Inclusion Criteria: patients in use of omeprazole prophylactic (off label or indicated use) who will be admitted at the hospital under study,

Exclusion Criteria: Patients transferred from another hospital or ward; those with prescheduled surgery; those unable to communicate (intubated, in isolation, or mentally disoriented); and those with a hospital stay ≤24 hours.

Hospitalized patients will be separated into three groups: those who make indicated and approved prophylactic use of omeprazole (exposed group 1), those who make not indicated and not approved prophylactic use (exposed group 2), and those who do not use the omeprazole (non-exposed group). Patients who do not make prophylactic use of omeprazole will be excluded. Patients will have their pharmacotherapy monitored and data will be collected daily using an investigation guide of the first day of admission and will be included in group 1 or 2, from the first use of omeprazole to discontinuation (washout period of seven half-lives or higher).