Objective: To assess the prevalence of pDDI involving antimicrobials and other standardized drugs in a large general hospital in the interior of São Paulo. Methods: quantitative study, with cross-sectional design and data collection by documentary analysis of hospital prescriptions from April to June 2017. Results: 66 clinically relevant pDDI were found, which corresponded to approximately 7.3% of antimicrobial prescriptions, being 93.9% (62) contraindicated / severe and 6.1% (4) moderate.

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... was no difference in the prevalence of clinically relevant pDDIs between critical and non-critical inpatient, in addition to all contraindicated interactions (10) having occurred in the clinical and surgical units. The most prevalent pDDI were, with respective degrees of documentation, between vancomycin and amikacin (47% - reasonable), clarithromycin and simvastatin (13.6% - good), and ciprofloxacin and simvastatin (7.6% - good). Conclusion: For the proper prevention of potential drug-related problems, mechanisms to guarantee the quality of prescriptions by trained clinical pharmacists are of fundamental importance, in addition to alert systems and drug interaction information for the health team, then ensuring quality pharmacotherapy and patient safety.