Discussion
This study demonstrates that both chloroquine and hydroxychloroquine carry cardiac safety risks that are of significant concern in the context of therapeutic doses being proposed for treatment of COVID-19. Furthermore, the proarrhythmic risk associated with block of hERG channels by these compounds can be exacerbated in patients by electrolyte abnormalities such as hypokalaemia and hypermagnesemia. Co-administration of azithromycin with hydroxychloroquine did not further increase prolongation of repolarisation to hydroxychloroquine alone in the short term. However, there was a time-dependent increase in prolongation observed with long term exposure, supporting the need for long term QT interval monitoring in these patients.