FDA contraindication for remdesivir and hydroxychloroquine (HCQ): immediate impact on current HCQ research
Simon Collins, HIV i-Base
On 15 June 2020, the US FDA issued a warning over a potential serious drug interaction between remdesivir and hydroxychloroquine that makes the two drugs contraindicated. 
The warning is based on a recently completed study that showed that HCQ could reduce concentrations of remdesivir, although further details on the interaction are not given
This should stop continued enrolment into ongoing HCQ studies in settings where remdesivir is available (if any such studies are still continuing).
Access to remdesivir as a proven and approved treatment now outweighs the scientific interest in HCQ, however novel the original study design, especially given recent reports that HCQ has no activity against COVID-19. 
The FDA also revoked the Emergency Use Authorisation (EUA) that was issued in March 2020 to enable access and research into HCQ for COVID-19. 
The Liverpool Drug Interaction databases (both for HIV and COVID-19) categorise this DDI as serious with a red alert contraindication.
Ongoing HCQ studies need to rapidly consider best outcomes for their participants that will prioritise immediate access to remdesivir as an FDA-approved active drug compared to scientific interest in HCQ as an investigational drug that has now reported outcomes that are worse than standard of care (ie no intervention).
This should limit further randomisations to studies that include HCQ arms when remdesivir is now available.
This article was first published online on 16 June 2020.
- Coronavirus (COVID-19) update: FDA warns of newly discovered potential drug interaction that may reduce effectiveness of a COVID-19 treatment authorized for emergency use (15 June 2020).
- Collins S. UK RECOVERY study stops hydroxychloroquine (HCQ) for COVID-19: more than 1100 deaths question ethics and safety overall. HTB early access (6 June 2020).
- FDA announcement. Coronavirus (COVID-19) update: FDA revokes emergency use authorization for chloroquine and hydroxychloroquine. (15 June 2020).