Description

Hydroxychloroquine Sulphate is a synthetic drug that is a derivative of chloroquine. It is primarily classified as a disease-modifying antirheumatic drug (DMARD) and an antimalarial agent. The “Sulphate” refers to the salt form of the drug, which is used for enhanced stability and bioavailability. Hydroxychloroquine is known for its effectiveness in treating a range of autoimmune diseases and is generally considered to have a better safety profile than chloroquine.

Indications

Hydroxychloroquine is indicated for the treatment of several conditions, including both parasitic infections and autoimmune diseases. Its key indications include:

• Rheumatoid Arthritis (RA): It is used as a long-term treatment for RA to reduce inflammation, pain, and swelling, and to slow down joint damage.

• Systemic Lupus Erythematosus (SLE): It is a cornerstone of therapy for SLE, where it is used to manage skin and joint symptoms, and to prevent disease flares.

• Malaria: It is used for the prophylaxis (prevention) and treatment of certain types of malaria, particularly in areas where the malarial parasites are susceptible.

Mechanism of Action

The exact mechanism of action of hydroxychloroquine, particularly in autoimmune diseases, is not fully understood, but it is known to have both anti-inflammatory and immunomodulatory effects.

1. Antimalarial Action:
   • Hydroxychloroquine accumulates in the acidic food vacuoles of the malarial parasite.
   • It inhibits the polymerization of heme (a toxic byproduct of hemoglobin digestion) into a non-toxic compound called hemozoin.

1. • This leads to a buildup of toxic heme within the parasite, which damages the parasite’s cell membranes and eventually kills it.
2. Immunomodulatory Action (for Autoimmune Diseases):
   • Interference with Lysosomes: Hydroxychloroquine is a weak base that accumulates in the lysosomes of immune cells (like antigen-presenting cells) and raises their pH. This raised pH interferes with the function of lysosomal enzymes, which are crucial for processing antigens.
   • Inhibition of Antigen Presentation: By altering the lysosomal pH and enzyme activity, hydroxychloroquine interferes with the presentation of antigens to T-cells. This reduces the activation of T-cells and the subsequent autoimmune response.

• • Inhibition of Cytokine Production: It is also believed to inhibit the production of pro-inflammatory cytokines, such as interleukin-1 (IL1​) and tumor necrosis factor-alpha (TNF-α), which are key mediators of inflammation in autoimmune diseases.
  • Other Effects: It may also interfere with Toll-like receptors (TLRs), which are part of the innate immune system, further contributing to its anti-inflammatory effects.

In summary, hydroxychloroquine has a dual-purpose mechanism: for malaria, it poisons the parasite by inhibiting heme detoxification, and for autoimmune diseases, it modulates the immune system by interfering with antigen processing and reducing the production of inflammatory mediators.