Watch for QT-prolonging drug interactions in older women prescribed quinolones

Urinary tract infections (UTIs) are the most common infection diagnosed in long-term care settings. Guidelines for managing uncomplicated UTI do not include fluoroquinolone antibiotics as one of the first-line choices for empiric antimicrobial selection. Reasons for this include increasing antimicrobial resistance, an increased tendency to cause Clostridioides difficile infection, and rare but serious adverse effects such as ruptured aorta, tendinopathy or tendon rupture, psychosis, hypoglycemia, peripheral neuropathy and retinal detachment. Fluoroquinolone antibiotics are also associated with QT-interval prolongation and torsades de pointes, a serious and potentially fatal arrhythmia. Risk factors include female sex, older age and use of other QT-interval prolonging medications. Older women living in long-term care are known to be at increased risk of QT-interval prolongation or serious arrhythmia due to the presence of risk factors including advanced age and female sex. It is uncertain how often older women residing in long-term care who are prescribed fluoroquinolones are also prescribed other medications that can potentially prolong the QT-interval. To investigate this issue, Canadian researchers recently described QT-interval prolonging drug interactions when women who resided in long-term care were prescribed fluoroquinolones for uncomplicated UTIs.The retrospective cohort study examined administrative health data from the Nova Scotia Seniors’ Pharmacare program over a 15-year period (January 2005–March 2020). The cohort included women (age ≥ 65 years) residing in long-term care who were dispensed a fluoroquinolone antibiotic within five days of an uncomplicated UTI diagnosis, based on physician billing data. Data on other drugs dispensed 30 and 90 days after the fluoroquinolone were also collected to identify drug interactions that had the potential to increase QT-interval prolongation risk. Results showed the following:A total of 15,276 unique uncomplicated UTI events occurred in 7,078 women over 15 years of follow-up.Fluoroquinolones were dispensed in 22.2% (n=3,454) of the uncomplicated UTI events.The most frequently dispensed fluoroquinolone was ciprofloxacin (n=2,923, 84.6% of fluoroquinolone dispensations) followed by norfloxacin (n~345, ~10% of fluoroquinolone dispensations).Annual dispensation of fluoroquinolones (between 2005 and 2020) ranged from 12%–28% of antibiotic dispensations for presumed uncomplicated UTI.The proportion of fluoroquinolone dispensations associated with a potential QT-interval prolonging drug interaction increased over time (p=0.00007).Within 30 days of the fluoroquinolone dispensation, the most common drug interactions identified that could increase QT-prolongation risk were with: furosemide (n=702, 20.3% of fluoroquinolone–drug interactions), citalopram (n=566, 16.4% of fluoroquinolone–drug interactions), and trazodone (n=461, 13.3% of fluoroquinolone–drug interactions).The authors concluded that an increasing proportion of women dispensed a fluoroquinolone for uncomplicated UTI experienced a potential QT-interval prolonging drug interaction over the study period. They stress the importance of judicious prescribing of fluoroquinolones in this patient population and limiting use of fluoroquinolones in older women with uncomplicated UTIs to avoid serious arrhythmia. When fluoroquinolones are prescribed for older women, the authors advise addressing potentially modifiable risk factors for torsades de pointes and close monitoring.Reference:Trenaman SC, von Maltzahn M, Stewart SA, et al. A description of QT-interval prolonging drug interactions with fluoroquinolones in older women with uncomplicated urinary tract infections. Can Geriatr J 2025;28:228-34. (accessed September 4, 2025).

Watch for QT-prolonging drug interactions in older women prescribed quinolones

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