Fig. 1.

Comparison of structures and metabolism of Hydroxychloroquine (HCQ) and Chloroquine (CQ): Both HCQ and CQ have a very similar, basic, and a flat aromatic structure. The only difference is the presence of an additional hydroxyl (−OH) group in HCQ as highlighted by the blue oval in the representation. Dealkylation of HCQ and CQ are mediated by Cytochrome P450 enzymes in the liver. HCQ produces two first-stage metabolites instead of just one. The two metabolites are Desthylhydroxychloroquine and Desthylchloroquine. Desthylchloroquine is also the first-stage metabolite product of CQ. Both the first-stage metabolites are further metabolized to a common product, Bisdesthylchloroquine