Chloroquine

Chloroquine is a 4-aminoquinoline antimalarial medication used to prevent and treat malaria caused by susceptible Plasmodium species. It is also prescribed for certain autoimmune diseases, including rheumatoid arthritis and systemic lupus erythematosus, where it helps modulate the immune response. Its effectiveness for malaria has diminished in many regions due to widespread resistance, though it remains useful in areas where parasites are still sensitive to the drug.

Mechanism and pharmacokinetics: chloroquine concentrates in the parasite’s food vacuole and inhibits the detoxification of heme by blocking the conversion of heme to hemozoin, leading to toxic heme buildup and parasite death. It is well absorbed orally and distributes extensively in body tissues, with a long elimination half-life and slow clearance. The drug crosses the placenta and is excreted in breast milk.

Clinical use: for malaria, dosing depends on the Plasmodium species and local resistance patterns; it is commonly used for prophylaxis in travelers to chloroquine-sensitive regions and for treatment of certain non-falciparum infections or sensitive falciparum infections in appropriate settings. In autoimmune diseases, it is prescribed for long-term low-dose therapy to reduce disease activity and may reduce the need for steroids, with regular monitoring for toxicity.

Safety and resistance: adverse effects often include gastrointestinal upset, headache, and skin rashes. Long-term use carries risks of retinal toxicity and corneal deposits; there is also potential for cardiomyopathy, electrolyte disturbances, and QT interval prolongation. Because of resistance, chloroquine is no longer a first-line antimalarial in many countries and is used where susceptibility is confirmed or in specific regimens. It is generally considered safe in pregnancy when indicated for malaria management in regions with sensitive parasites. Related drug hydroxychloroquine has a similar mechanism but a distinct safety profile.