BACKGROUND: Improper use of antimicrobials can cause adverse drug events and high costs. The purpose of this study was to investigate the frequency and potential drug–drug interactions associated with antimicrobials among hospitalized patients.

MATERIAL AND METHODS: This study was conducted on the same day in 5 different hospitals in Turkey. We included patients aged ³18 years who received at least 1 antimicrobial drug and at least 1 of any other drug. The Micromedex® online drug reference system was used to control and describe the interactions. Drug interactions were classified as contraindicated, major, moderate, and minor.

RESULTS: Potential drug–drug interactions with antimicrobials were 26.4% of all interactions. Five (42%) of 12 contraindicated interactions and 61 (38%) of 159 major interactions were with antimicrobials. Quinolones, triazoles, metronidazole, linezolid, and clarithromycin accounted for 173 (25.7%) of 673 prescribed antimicrobials, but were responsible for 141 (92.1%) of 153 interactions. In multivariate analysis, number of prescribed antimicrobials (odds ratio: 2.3001, 95% CI: 1.6237–3.2582), number of prescribed drugs (odds ratio: 1.2008, 95% CI: 1.0943–1.3177), and hospitalization in the university hospital (odds ratio: 1.7798, 95% CI: 1.0035–3.1564) were independent risk factors for developing drug interactions.

CONCLUSIONS: Due to risk of drug interactions, physicians should be more cautious when prescribing antimicrobials, particularly when prescribing quinolones, linezolid, azoles, metronidazole, and macrolides.

Keywords: Anti-Infective Agents, Drug Interactions, Polypharmacy