Table 1.

Pre-clinical readouts from the key in vitro studies investigating therapeutic efficacy of HCQ against SARS-CoV-2. HCQ, Hydroxychloroquine; EC50, Effective concentration; AZM, Azithromycin.

Investigation/References	Cell Systems	Drug, Concentration, and Assay Time (h)	Study Control	Key Findings/Comments
Yao et al. 2020	Vero E6 cell (Origin-African green Monkey)	CQ and HCQ 0.032, 0.16, 0.80, 4, 20, & 100 µM 2 h	-	-HCQ showed better SARS-CoV-2 inhibitory activity than CQ. -An extended incubation period may produce greater anti-viral effect
Liu et al. 2020	Vero E6 Cells	CQ and HCQ 0.068, 0.21, 0.62, 1.85, 5.56, 16.67, and 50 µM 1 h	PBS (Phosphate buffer saline)	-HCQ inhibited the steps including infection/entry and post-infection -At the higher viral replication rate, anti-viral efficacy of HCQ found to be lesser than of CQ
Wang et al. 2020	Vero E6 Cells	CQ and others * 0.01, 0.05, 0.1, 0.5, 1, 5, and 10 µM 1 h	DMSO	-HCQ inhibited the viral activity at low µM conc. (effective conc. EC50 = 1.13 μM) -CQ effectively inhibited SARS-CoV-2 infection in vitro
Andreani et al. 2020	Vero E6 cells	CQ- 1, 2 or 5 μM associated with 5 or 10 μM for azithromycin.	-	Combination of hydroxychloroquine and azithromycin has a synergistic effect in vitro on SARS-CoV-2 at concentrations
Keyaerts et al. 2004 (*Earliest report from the SARS-CoV)	Vero E6 cell	CQ 0, 0.8, 4, 20, & 100 µM 8 h to 3 days	-	-CQ potently inhibits SARS-CoV activity at a lesser (8.8 ± 1.2 μM) concentration than its cytostatic activity (261.3 ± 14.5 μM) -Addition of CQ even after 5 h of SARS-CoV infection could yet be inhibitory active