Hydroxychloroquine, known by brand names like Plaquenil or Sovuna, is an antimalarial drug. It was initially developed for malaria but is also recognized as a disease-modifying antirheumatic drug (DMARD). It is prescribed for certain autoimmune diseases and for the prevention and treatment of malaria. Available as an oral tablet, dosages typically range from 100 mg to 400 mg.
Conditions It Treats
Hydroxychloroquine is commonly prescribed for autoimmune diseases and malaria. While historically used for malaria, a parasitic infection, its use for autoimmune disorders has become more prevalent. It is still indicated for uncomplicated malaria, especially in regions without chloroquine resistance.
The medication manages systemic lupus erythematosus (SLE), an autoimmune disease where the immune system attacks various body tissues. It also treats discoid lupus erythematosus, a form of lupus mainly affecting the skin. For rheumatoid arthritis, a condition where the immune system damages joints, hydroxychloroquine helps reduce inflammation and pain. Its benefits in these autoimmune conditions include reducing inflammation and modulating the immune response.
Its Mechanism of Action
Hydroxychloroquine works in multiple ways for both autoimmune conditions and malaria. In autoimmune diseases, it primarily functions as an immunomodulatory agent, helping to calm an overactive immune system. It achieves this by accumulating in acidic compartments within cells, such as lysosomes, which then raises their pH. This change in pH interferes with antigen processing and presentation, reducing the immune system’s ability to trigger an inflammatory response.
Hydroxychloroquine also inhibits Toll-like receptor (TLR) signaling, specifically TLR7 and TLR9, which are involved in immune activation. By interfering with these pathways, it decreases the production of pro-inflammatory cytokines like TNF-α, IL-1, and IL-6, thereby reducing inflammation. When treating malaria, hydroxychloroquine concentrates in the parasite’s food vacuole, preventing the detoxification of heme, a substance toxic to the parasite, ultimately leading to its death.
Important Safety Considerations
Hydroxychloroquine is generally well-tolerated, but patients should be aware of potential side effects. Common side effects include nausea, stomach cramps, and diarrhea, which may lessen over time. Other possible side effects include skin rash, hair changes, and muscle weakness.
A more serious, though rare, concern with long-term use is retinal damage, known as ocular toxicity, which can lead to permanent vision loss. This risk increases with higher daily doses, longer treatment duration (over five years), age over 60, and existing kidney or liver problems. Regular eye examinations are highly recommended, with a baseline exam at the start of treatment and annual follow-up exams after five years, or more frequently if risk factors are present. These exams often involve tests like optical coherence tomography (OCT) to detect early retinal changes.
It is important to discuss all medications, including over-the-counter drugs and herbal supplements, with a healthcare provider, as hydroxychloroquine can interact with certain other medicines. For instance, it can affect blood sugar levels and may interact with medications that influence heart rhythm, potentially leading to dangerous heart rhythm problems. Hydroxychloroquine should only be used under medical supervision, and patients should consistently communicate any concerns or changes in their health with their doctor.