Chloroquine drug, molecular model. This medication is used for the prevention and treatment for malaria. Other uses include treatment of rheumatoid arthritis, lupus, and porphyria cutanea tarda. It is a candidate for an experimental treatment for coronavirus disease 2019 (COVID-19). The chemical formula is C18.H26.Cl.N3. Atoms are colour-coded: dark grey (carbon), light grey (hydrogen), blue (nitrogen) and green (chlorine).