hydroxychloroquine

Hydroxychloroquine is an antimalarial medication in the 4-aminoquinoline class and a derivative of chloroquine. It is approved for malaria prophylaxis and treatment in certain contexts and is widely used for autoimmune diseases.

Medical uses include prevention and treatment of malaria in areas where chloroquine resistance is not complete, and, more prominently in many countries, treatment of autoimmune conditions such as rheumatoid arthritis and systemic lupus erythematosus. It is also employed for some dermatologic disorders. In autoimmune diseases, it is valued for its disease-modifying and anti-inflammatory effects and is often used as part of long-term management.

The mechanism of action is not fully understood. It is believed to accumulate in lysosomes, raising their pH and interfering with lysosomal activity. This can reduce antigen presentation and modulate immune cell function, contributing to anti-inflammatory effects. The clinical benefits in autoimmune diseases are thought to arise from these immunomodulatory actions rather than direct antimicrobial activity.

Safety and adverse effects are important considerations. Long-term use is associated with a risk of retinal toxicity, making regular ophthalmologic screening recommended for patients on extended therapy. Other potential adverse effects include gastrointestinal upset, headache, skin rash, hypoglycemia, and, less commonly, cardiac effects such as QT prolongation and cardiomyopathy, particularly with higher doses or concomitant medications. It is generally avoided in patients with known retinal disease or certain heart or kidney conditions and requires caution in pregnancy and lactation.

During the COVID-19 pandemic, hydroxychloroquine was studied for treatment and prevention but did not demonstrate consistent clinical benefit in high-quality trials and usage outside trials declined due to safety concerns.