When is it necessary to monitor the QTc interval in patients on hydroxychloroquine?

The answer to this question is not straightforward mainly because there are limited data in this area. Hydroxychloroquine and Chloroquine directly affect cardiac repolarization and are associated with QT prolongation. Given this, there is an argument for getting a baseline ECG for patients initiatin...

All good points mentioned by others. Few additional comments:

There are multiple cardiac conduction abnormalities including QTc prolongation have been reported with use of hydroxychloroquine (HCQ). A recent meta-analysis of HCQ use in COVID-19 alone or in combination with azithromycin was associated...