Also Known As: Hydroxychloroquine, Plaquenil, Axemal, Dolquine, Quensyl
Hydroxychloroquine is an antimalarial drug, sold under the trade names Plaquenil, Axemal (in India), Dolquine, and Quensyl, also used to reduce inflammation in the treatment of rheumatoid arthritis (see disease-modifying antirheumatic drugs) 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. It is available for oral administration as hydroxychloroquine sulfate (plaquenil) of which 200 mg contains 155 mg base in chiral form. Hydroxychloroquine has similar pharmacokinetics to chloroquine, with quick gastrointestinal absorption and is eliminated by the kidney. Cytochrome P450 enzymes (CYP 2D6, 2C8, 3A4 and 3A5) N-desethylated Hydroxychloroquine to Ndesethylhydroxychloroquine.
Hydroxychloroquine is classified as an anti-malarial medication and is one of a number of drugs that have been used for many years in the treatment of malaria. It is also useful in treating systemic lupus erythematosus, rheumatic disorders like rheumatoid arthritis and Sjögren's Syndrome, and porphyria cutanea tarda. While hydroxychloroquine has been known for some time to increase lysosomal pH in antigen presenting cells, its mechanism of action in inflammatory conditions has been recently elucidated and involves blocking the activation of 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. Hydroxychloroquine, by decreasing TLR signaling, reduces the activation of dendritic cells thus mitigating the inflammatory process.
Hydroxychloroquine is also widely used in the treatment of post-Lyme arthritis that can be induced by Lyme disease. The action of the drug may involve both an anti-spirochaete activity and an anti-inflammatory activity, similar to the treatment of rheumatoid arthritis.