RATIONALE, AIMS AND OBJECTIVES:In recent years, the use of proton pump inhibitors (PPI), especially omeprazole, has been associated with development of chronic kidney disease (CKD). These drugs are widely used worldwide. Although some studies have found an association between the use of PPI and the onset of acute renal failure and CKD. This study aims to analyze the association between the continuous use of omeprazole and the progression of CKD in adult and elderly individuals. METHOD:A retrospective cohort study was conducted with patients followed up at a nephrology clinic in Brazil, in 2016 and 2017. Information about clinical and sociodemographic data, health behaviors, and medication use were collected from all patients diagnosed with CKD through consultation of medical charts and the Brazilian health information system (SIS). The participants were allocated into two groups: users and non-users of omeprazole, and the progression of CKD was then evaluated for each group. In the bivariate analysis, the Mann-Whitney U test to compare the quantitative variables between groups, and the Pearson/Fisher two-tailed chi-square test to compare the categorical variables were applied. Multivariate analysis was performed using Cox regression. RESULTS:A total of 199 CKD patients were attended in the polyclinic, and of these, 42.7% were omeprazole users. There was a higher percentage of CKD progression in users (70.6%) compared to non-users (10.5%). The hazard ratio was 7.34 (CI: 3.94-13.71), indicating a higher risk of progression to worse stages of CKD in omeprazole users than in non-users. As for the other variables, no statistically significant difference was found between groups (p > 0.05). CONCLUSION:An association between omeprazole use and progression of CKD stage was identified, showing a higher risk of disease evolution among omeprazole users.