Conclusion and implications:
Combined HCQ+AZM treatment exerts pro-arrhythmic ventricular events by synergetically inhibiting IKr, IKs with resulting effects on cellular Ca2+ signalling, and action potential propagation and duration. These findings provide an electrophysiological basis for recent FDA cardiac safety guidelines cautioning against combining HCQ/AZM when treating Covid-19.
Key words: Cardiac safety; Ion channels, Hydroxychloroquine; Azithromycin, CiPA, COVID-19
Introduction
The severe acute respiratory( syndrome coronavirus 2 (SARS-CoV-2) pandemic has now infected >6.34 million individuals causing 380 810 deaths as of 3-June-2020 (www.ecdc.eurpoe.eu). Although there are no approved drugs to prevent or treat SARS-CoV-2 infection, recent use of the anti-malarial 4-aminoquinolines chloroquine (CQ) or hydroxychloroquine (HCQ) alone, or combined with the antibiotic azithromycin (AZM) in Covid-19 therapy has attracted global attention and extensive early clinical use and trials(NIH, 2020; Pharmafield, 2020). An initial nonrandomized open label clinical trial of 20 cases, had associated HCQ treatment with viral load reduction or disappearance in COVID-19 patients, effects reinforced by AZM(Gautret et al., 2020). This subsequently prompted the US Food and Drugs Administration (FDA) authorization of emergency use of CQ or HCQ, alone or in combination with AZM in Covid-19 therapy(Hinton, 2020; Lenzer, 2020). Currently, large number of trials of these combinations, with or without the addition of further drugs, are registered worldwide (NIH, 2020; Pharmafield, 2020).
However, several recent studies have flagged cardiac safety concerns for the CQ/HCQ and AZM regime in Covid-19 therapy. Particular concern has arisen regarding potential synergistic effects of HCQ and AZM on QT duration and cardiovascular mortality (Borba et al., 2020; Chorin et al., 2020; Lane et al., 2020; Magagnoli et al., 2020; Mercuro et al., 2020). Higher mortalities and incidences of prolonged corrected QT (QTc) intervals were reported in patients at a Brazilian hospital receiving the high dose (12 g total dose over 10 days, ~1.2 g/day, giving plasma levels of ~10 µM) than the lower dose of CQ, typified by its use in other conditions such as rheumatoid arthritis and systemic lupus erythematosus (SLE). This phase 2b randomized Covid-19 trial was terminated after enrolment of only 81 out of the target of 440 patients owing to occurrences of adverse events (Borba et al., 2020). A retrospective data analysis from United States Veterans Health Administration medical centers suggested increased overall mortality even in patients treated with HCQ alone (Magagnoli et al., 2020). The largest available analysis from an international consortium on HCQ safety covering over 950,000 patients from six countries declared HCQ safe for short-term use at doses currently used for conditions such as rheumatoid arthritis. However, it urged caution in its use when combined with AZM in view of potential risks of cardiovascular mortality related to QTc prolongation (Lane et al., 2020). Two recent reports of 90 and 201 patients hospitalized with COVID-19 treated with HCQ, with or without AZM, associated these drugs with QTc prolongation, especially when used in combination (Mercuro et al., 2020; Saleh et al.). Although these studies are small, only one case of torsades de pointes was documented and the therapy was seldom discontinued. They suggested that more QT interval monitoring studies should be undertaken before final recommendations can be made(Saleh et al.). Based on these findings, the FDA issued a cautions warning against use of HCQ or CQ for COVID-19 outside of the hospital setting or a clinical trial, due to risks of heart rhythm problems(Hinton, 2020). This does not affect FDA-approved uses in malaria, systemic lupus erythematosus (SLE), and rheumatoid arthritis where they have been used many years. Both HCQ and AZM have been in clinical use alone or in combination in other disease conditions for many years with cardiac safety then not considered a major concern.
Currently, there is very limited data evaluating cardiac safety particularly concerning use of HCQ in combination with AZM, although multiple randomized trials are currently in progress evaluating the efficacy of this combination for Covid-19. We therefore explored the cardiac safety of HCQ alone or in combination with AZM using the FDA recommended Comprehensive in Vitro Proarrhythmia Assay (CiPA) protocols to understand arrhythmic mechanisms (Strauss et al., 2018). Furthermore, we expanded the CiPA protocol by introducing assessments of effects on membrane and Ca2+ clocks, their interaction and cardiac conduction recently suggested as crucial indicators for ventricular arrhythmogenesis (Lei & Huang, 2019; Lei, Wu, Terrar & Huang, 2018).