Hydroxychloroquine is a 4-aminoquinoline derivative with antimalarial, anti-inflammatory, and immunomodulatory properties. It interferes with lysosomal activity, antigen presentation, and Toll-like receptor signalling, accounting for its dual utility across infectious and autoimmune indications. Indicated for the prophylaxis and treatment of acute attacks of malaria due to susceptible Plasmodium species, and as a disease-modifying agent in rheumatoid arthritis, systemic lupus erythematosus, and chronic discoid lupus erythematosus.