Hydroquin 200 mg Tablet is also used for the treatment of rheumatoid arthritis (a chronic condition that involves swelling and pain in the small joint) and systemic lupus erythematosus (a chronic inflammatory condition that occurs when your immune system attacks the body causing skin rash, joint pain, and tiredness). Hydroxychloroquine at a dose of 400 mg is also used as an additional treatment for type-2 diabetes (high blood sugar levels that may occur when your body does not use the insulin it makes properly to move sugar from the blood into the cells).