COVID-19: QTc prolongation risk is high with hydroxychloroquine, azithromycin treatment

  • Mercuro NJ & al.
  • JAMA Cardiol
  • 1 May 2020

  • curated by Emily Willingham, PhD
  • Clinical Essentials
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  • Hydroxychloroquine treatment carries increased risk for QTc prolongation in patients with COVID-19 pneumonia, according to the findings of this cohort study.
  • Adding azithromycin to the regimen enhanced this risk.

Why this matters

  • Editorial: treatment decisions for this disease will continue to be based on clinical judgment and, ideally, in the context of enrolling patients into clinical trials to provide definitive answers.

Key results

  • 90 patients received hydroxychloroquine, and 53/90 also received azithromycin.
  • 48.9% were female; mean age was 60.1 years.
  • Mean BMI was 31.5 kg/m2.
  • 53.3% had hypertension, 28.9% had diabetes.
  • 26% were mechanically ventilated.
  • Most were taking some QTc-prolonging medication.
  • Baseline median QTc was 455 (interquartile range, 430-474) milliseconds.
    • With hydroxychloroquine alone, this median was 473 (454-487) milliseconds with posttreatment QTc peak of 479.5 (443.5-501.5) milliseconds.
    • With azithromycin added, it was 442 (427-461) milliseconds with posttreatment QTc peak of 458 (449-492) milliseconds.
    • Changes in QTc on both treatments were significantly higher than with hydroxychloroquine alone, +23 (10-40) vs +5.5 (−14 to 31) milliseconds (P=.03).
  • 7 patients on hydroxychloroquine alone had QTc that exceeded 500 milliseconds and was prolonged.
    • 11 of those receiving both drugs had this outcome.
    • Prolonged QTc was more likely with concomitant use of loop diuretics (P=.03) or baseline QTc ≥450 milliseconds (P=.008).
  • 10 patients discontinued hydroxychloroquine treatment, including 1 who developed torsades de pointes.

Study design

  • Cohort study at an academic center in Boston, Massachusetts.
  • Funding: None disclosed.


  • Causation not established.
  • Higher-risk patients probably underrepresented.