COVID-19 Drugs Chloroquine and Hydroxychloroquine, but Not Azithromycin and Remdesivir, Block hERG Potassium Channels

J Pharmacol Exp Ther. 2021 May;377(2):265-272. doi: 10.1124/jpet.120.000484. Epub 2021 Mar 5.


Drug-induced long QT syndrome (LQTS) is an established cardiac side effect of a wide range of medications and represents a significant concern for drug safety. The rapidly and slowly activating delayed rectifier K+ currents, mediated by channels encoded by the human ether-a-go-go-related gene (hERG) and KCNQ1 + KCNE1, respectively, are two main currents responsible for ventricular repolarization. The common cause for drugs to induce LQTS is through impairing the hERG channel. For the recent emergence of COVID-19, caused by severe acute respiratory syndrome coronavirus 2, several drugs have been investigated as potential therapies; however, there are concerns about their QT prolongation risk. Here, we studied the effects of chloroquine, hydroxychloroquine, azithromycin, and remdesivir on hERG channels. Our results showed that although chloroquine acutely blocked hERG current (IhERG), with an IC50 of 3.0 µM, hydroxychloroquine acutely blocked IhERG 8-fold less potently, with an IC50 of 23.4 µM. Azithromycin and remdesivir did not acutely affect IhERG When these drugs were added at 10 µM to the cell culture medium for 24 hours, remdesivir increased IhERG by 2-fold, which was associated with an increased mature hERG channel expression. In addition, these four drugs did not acutely or chronically affect KCNQ1 + KCNE1 channels. Our data provide insight into COVID-19 drug-associated LQTS and cardiac safety concerns. SIGNIFICANCE STATEMENT: This work demonstrates that, among off-label potential COVID-19 treatment drugs chloroquine, hydroxychloroquine, azithromycin, and remdesivir, the former two drugs block hERG potassium channels, whereas the latter two drugs do not. All four drugs do not affect KCNQ1 + KCNE1. As hERG and KCNQ1 + KCNE1 are two main K+ channels responsible for ventricular repolarization, and most drugs that induce long QT syndrome (LQTS) do so by impairing hERG channels, these data provide insight into COVID-19 drug-associated LQTS and cardiac safety concerns.

MeSH terms

  • Adenosine Monophosphate / analogs & derivatives*
  • Adenosine Monophosphate / pharmacology
  • Adenosine Monophosphate / therapeutic use
  • Alanine / analogs & derivatives*
  • Alanine / pharmacology
  • Alanine / therapeutic use
  • Anti-Bacterial Agents / pharmacology
  • Anti-Bacterial Agents / therapeutic use
  • Antimalarials / pharmacology
  • Antimalarials / therapeutic use
  • Antiviral Agents / pharmacology
  • Antiviral Agents / therapeutic use
  • Azithromycin / pharmacology*
  • Azithromycin / therapeutic use
  • COVID-19 / metabolism
  • COVID-19 Drug Treatment*
  • Chloroquine / pharmacology*
  • Chloroquine / therapeutic use
  • Dose-Response Relationship, Drug
  • ERG1 Potassium Channel / antagonists & inhibitors*
  • ERG1 Potassium Channel / metabolism
  • HEK293 Cells
  • Humans
  • Hydroxychloroquine / pharmacology*
  • Hydroxychloroquine / therapeutic use
  • Potassium Channel Blockers / pharmacology
  • Potassium Channel Blockers / therapeutic use


  • Anti-Bacterial Agents
  • Antimalarials
  • Antiviral Agents
  • ERG1 Potassium Channel
  • KCNH2 protein, human
  • Potassium Channel Blockers
  • remdesivir
  • Adenosine Monophosphate
  • Hydroxychloroquine
  • Azithromycin
  • Chloroquine
  • Alanine