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. 2025 Sep 3;28(3):228-234.
doi: 10.5770/cgj.28.835. eCollection 2025 Sep.

A Description of QT-Interval Prolonging Drug Interactions with Fluoroquinolones in Older Women with Uncomplicated Urinary Tract Infections

Shanna C Trenaman  1   2 , Maia von Maltzahn  2   3 , Samuel Alan Stewart  4 , Hala Tamim  5 , Ingrid Sketris  1 , Emily Black  1
Affiliations

A Description of QT-Interval Prolonging Drug Interactions with Fluoroquinolones in Older Women with Uncomplicated Urinary Tract Infections

Shanna C Trenaman et al. Can Geriatr J. .

Abstract

Background: Fluoroquinolone (FQ) antibiotics are associated with QT-interval prolongation and Torsades de Pointes (TdP). Female sex, older age, and other QT-interval prolonging medications further increase risk for TdP. Our aim was to describe QT-interval prolonging drug interactions when FQs were dispensed to women who resided in long-term care (LTC) for uncomplicated urinary tract infections (UTIs).

Methods: This retrospective cohort study used administrative health data from the Nova Scotia Seniors' Pharmacare program from January 2005 through March 2020. The cohort included women residing in LTC dispensed a FQ antibiotic within five days of a diagnostic code for an uncomplicated UTI in physician billing data. Additional drug dispensations were collected 30 and 90 days after the FQ to identify drug interactions that resulted in potentially increased QT-interval prolongation risk. Drug interactions were described. A Mann-Kendall trend test assessed the change in the frequency of FQ-drug interactions over the study period.

Results: Annual dispensation of FQs ranged from 12-28% of antibiotic dispensations for presumed uncomplicated UTI. The proportion of FQ dispensations associated with a QT-interval prolonging drug interaction increased over time (p=.00007). Within 30 days of the FQ dispensation, the most common drug interactions identified were: furosemide (n=702, 20.3% of FQ-drug interactions), citalopram (n=566, 16.4% of FQ-drug interactions), and trazodone (n=461, 13.3% of FQ-drug interactions).

Conclusions: An increasing proportion of women dispensed a FQ for uncomplicated UTI experienced a potential QT-interval prolonging drug interaction over the study period. When prescribing FQs to older women, addressing potentially modifiable risk factors for TdP, and monitoring closely, is warranted.

Keywords: Torsades de pointes; drug interaction; fluroquinolone; long-term care.

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Conflict of interest statement

CONFLICT OF INTEREST DISCLOSURES: Emily Black has received funding to support research projects unrelated to this work from Pfizer Canada and Shoppers Drug Mart. Ingrid Sketris has received research grant support from the Drug Evaluation Alliance of Nova Scotia and salary support from the Canadian Network for Observational Drug Effect Studies (CNODES). Shanna Trenaman has received research grant support from the Drug Evaluation Alliance of Nova Scotia for an unrelated research project. The remaining authors have no financial or personal relationships with commercial entities to disclose.

Figures

FIGURE 1
FIGURE 1
Proportion of UTI events treated with a fluoroquinolone that were involved in a potentially QT-interval prolonging drug interaction within 30 and 90 days of an uncomplicated urinary tract infection diagnosis in women 65 years of age and older who reside in long-term care
FIGURE 2
FIGURE 2
Top eight specific medications with known or conditional risk of QT-interval prolonging drug interactions with fluoroquinolone antibiotics between 2005 and 2019 in women 65 years of age and older who reside in long-term care
See this image and copyright information in PMC

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