Multivalent cations interactions with fluoroquinolones or tetracyclines: A cross-sectional study

Introduction: Oral fluoroquinolones and tetracyclines are known to interact with divalent or trivalent cation-containing compounds (DTCCs) via chelation. The objective of this study is to describe the prevalence of these drug-drug interactions (DDIs) in an inpatient setting. Methods: A cross-sectional study of prospectively collected data were conducted at an academic tertiary care hospital. We included hospitalized adults who were receiving oral fluoroquinolones or tetracyclines with DTCCs in 2019. Our hospital uses electronic health records for medication ordering and handwritten medication administration records (MARs). The primary study outcome was the percentage of simultaneous administration of fluoroquinolones or tetracyclines with DTCCs, and the secondary outcome was the percentage of inappropriate separation time. Results: Among patients who received oral fluoroquinolones or tetracyclines, 47 patients (26.6%) were co-administered DTCCs and included in this study. Ciprofloxacin (n = 29; 61.7%) was the most commonly interacting antibiotic, followed by moxifloxacin (n = 12; 25.5%) and doxycycline (n = 6; 12.8%). The interacting DTCCs included iron-containing products and calcium-containing products, and half of the patients (n = 24; 51%) received DTCCs once daily. Most patients (n = 35; 74.5%) were found to receive oral fluoroquinolones or tetracyclines at the same time as DTCCs, while one (2.1%) received inappropriately separated DTCCs. Conclusions: Despite being a very known contraindicated DDI, the prevalence of simultaneous co-administration of oral fluoroquinolones or tetracyclines with polyvalent cations was extremely high in a hospital with handwritten MARs. Antimicrobial stewardship programs should target this DDI, and future studies should evaluate the impact of different practical solutions to this problem in different clinical settings.