Hydroxychloroquine (HCQ)

Hydroxychloroquine is an antimalarial drug used to reduce inflammation in the treatment of rheumatoid arthritis and lupus. Hydroxychloroquine differs from chloroquine by the presence of a hydroxyl group at the end of the side chain: The N-ethyl substituent is beta-hydroxylated. Hydroxychloroquine has been used for many years to treat malaria. It is also used to treat systemic lupus erythematosus, rheumatic disorders like rheumatoid arthritis and Sjögren's Syndrome, and porphyria cutanea tarda. Hydroxychloroquine increases lysosomal pH in antigen presenting cells. In inflammatory conditions, it blocks toll-like receptors on plasmacytoid dendritic cells (PDCs). Toll-like receptor 9 (TLR 9), which recognizes DNA-containing immune complexes, leads to the production of interferon and causes the dendritic cells to mature and present antigen to T cells.