A Description of QT-Interval Prolonging Drug Interactions with Fluoroquinolones in Older Women with Uncomplicated...

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).

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.

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).

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.