(251) Assessment of fluoroquinolone related QT-interval prolonging drug interactions encountered when treating uncomplicated urinary tract infections in women residing in long-term care

Publication Number: 1242

Background: Fluoroquinolone (FQ) antibiotics are often selected for treatment of urinary tract infections (UTIs). When selecting FQ antibiotics, a close assessment of risk of QT-interval prolongation is indicated with attention to underlying reversible risk factors such as electrolyte imbalances and co-prescription of other QT-interval prolonging medications.

Objectives: The objective of this study was to explore and characterize QT-interval prolonging drug interactions when fluoroquinolones (FQ) were dispensed for uncomplicated urinary tract infections (UTIs) in women at least 65 years of age who resided in long-term care (LTC) in Nova Scotia, Canada.

Methods: The retrospective cohort study used administrative health data collected between January 2005 and March 2020. Dispensation data for women who were beneficiaries of the Nova Scotia Seniors’ Pharmacare Program, aged 65 years or older, residing in LTC and dispensed a FQ antibiotic within 7 days of a medical claim for an uncomplicated UTI were extracted. Drug interactions between FQ antibiotics and other medications implicated in potential QT-interval prolongation were captured annually (calendar year) when the interacting drug were dispensed within 30 days of the FQ. FQ-drug interactions were described descriptively and in terms of proportions of FQ dispensations. A Mann-Kendall trend test assessed for increasing or decreasing FQ-drug interactions over the 15-year period of follow-up.

Results: 15,276 uncomplicated UTI events were reported during the study period in 7,078 women. Yearly dispensation of FQs ranged from 12-27% of all antibiotic dispensations for uncomplicated UTI. The proportion of QT-interval prolonging drug interactions increased over time (p= 0.00007), peaking in 2018 with 80% of patients dispensed a FQ also dispensed a drug known to increase risk of a potential QT-interval prolonging drug interaction within 30 days of the FQ dispensation. The most common drug interactions with FQs identified included furosemide (n=592, 17.6% of FQ dispensations), citalopram (n=476, 14.2% of FQ dispensations), and trazadone (n=406, 12.1% of FQ dispensations).

Conclusions: The trend was for an increasing proportion of FQ dispensations to be within 30 days of a medication that increases the risk for a potential QT-interval prolonging drug interaction. When feasible, FQs should be avoided due to risk of drug-drug interactions, adverse events, and risk of resistance. When used, close assessment of risk, addressing underlying reversible risk factors (ie. electrolyte imbalances), and close monitoring should be done.