The Potential for QT Interval Prolongation with Chronic Azithromycin Therapy in Adult Cystic Fibrosis Patients

Introduction: Oral azithromycin (AZM) has been shown to reduce airway inflammation and disrupt biofilm formation. However, chronic AZM therapy may result in QT interval (QTc) prolongation. Objectives: The goals of this study were twofold: (i) to characterize the risk of QTc prolongation in adult patients with cystic fibrosis (CF) receiving AZM and other potential QTc-prolonging agents, and (ii) to describe and capture the number of potential QTc-prolonging agents patients with CF are prescribed. Methods: A retrospective study was conducted over a 3-year period in an adult CF center. QTc values were recorded from electrocardiograms. Univariate and multivariate analyses were conducted. Standard QTc prolongation definitions (males ≥ 450 msec, females ≥ 470 msec) were used. Results: A total of 89 adult CF patient's records were reviewed. Sixty-eight patients received chronic AZM therapy. Two male patients had prolonged QTc, but only 1 received chronic AZM therapy. The median QTc interval between patients receiving and not receiving AZM was not significantly different (405 [interquartile range, IQR: 388–425] vs 394 [IQR: 384–413] msec, respectively, p=0.14). Also, the QTc interval for patients taking chronic AZM 500 mg Monday/Wednesday/Friday or 250 mg daily was not significantly different (401 [IQR: 383–419] vs 409 [IQR: 394–427] msec, respectively, p=0.48). When stratified by the number of QTc-prolonging medications (AZM vs no AZM), there was no significant difference in median QTc values between patients receiving zero to ≥ 5 QTc-prolonging medications. Conclusion: An association between chronic AZM therapy and longer QTc intervals or significant QTc prolongation was not shown.