Antimalarials
Antimalarials
Antimalarials are a class of antiparasitic drugs used primarily to treat and prevent malaria, a disease caused by Plasmodium parasites transmitted by mosquitoes. These drugs act by targeting different stages of the parasite’s life cycle, mainly the blood stage, to kill or inhibit the parasite and prevent disease progression.
Mechanisms of Action
- Quinoline Antimalarials (e.g., chloroquine, quinine, mefloquine):
These drugs interfere with the parasite’s digestion of hemoglobin within red blood cells. Normally, the parasite breaks down hemoglobin, releasing toxic heme, which it detoxifies by polymerizing into hemozoin. Quinoline drugs inhibit this polymerization, causing toxic heme accumulation and parasite death. Quinine also intercalates into parasite DNA, disrupting replication and transcription13. - Artemisinin and Derivatives (e.g., artesunate, artemether):
Derived from Artemisia annua, artemisinins act rapidly by generating free radicals through interaction with iron in the parasite, damaging parasite proteins and membranes. They primarily target the trophozoite stage, leading to fast parasite clearance. Artemisinins are often used in combination therapies to prevent resistance2. - Other Mechanisms:
Some antimalarials accumulate in acidic parasite organelles (lysosomes/endosomes), raising pH and disrupting antigen processing and immune activation. They also exhibit immunomodulatory, anti-inflammatory, antiproliferative, and photoprotective effects, which explain their use in autoimmune diseases like lupus and rheumatoid arthritis5.
Clinical Uses
- Malaria Treatment and Prophylaxis:
Used to treat uncomplicated and severe malaria, and for prevention in travelers or populations in endemic areas. Combination therapies, especially those including artemisinins, are standard to combat drug resistance26. - Non-malarial Uses:
Due to their immunomodulatory properties, some antimalarials (e.g., hydroxychloroquine, chloroquine) are used in dermatology and rheumatology to treat autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis56.
Common Antimalarial Drugs
| Drug | Class | Mechanism of Action | Notes |
|---|---|---|---|
| Chloroquine | 4-aminoquinoline | Inhibits heme polymerization | Resistance common in many regions |
| Quinine | Quinoline | DNA intercalation; inhibits heme detoxification | Used for severe malaria |
| Mefloquine | Quinoline derivative | Disrupts parasite membranes and proteins | Neuropsychiatric side effects possible |
| Artemisinin | Sesquiterpene lactone | Generates free radicals damaging parasite | Rapid action; used in combination |
| Hydroxychloroquine | 4-aminoquinoline | Similar to chloroquine; immunomodulatory effects | Used in autoimmune diseases |
| Tafenoquine | 8-aminoquinoline | Active against liver stages and blood stages | Risk of hemolytic anemia in G6PD deficiency |
Side Effects and Resistance
- Side Effects:
Can include gastrointestinal upset, headache, dizziness, retinopathy (with long-term chloroquine use), hemolytic anemia (especially with tafenoquine in G6PD deficiency), and cardiac arrhythmias246. - Resistance:
Resistance to many antimalarials, including chloroquine and artemisinin derivatives, has emerged, particularly in Southeast Asia and parts of Africa, necessitating ongoing development of new drugs and combination therapies23.
Summary
Antimalarials are vital agents in malaria control, with diverse mechanisms targeting parasite survival. Their immunomodulatory properties extend their use beyond malaria to autoimmune and inflammatory diseases. The emergence of resistance remains a major challenge, underscoring the need for novel therapies and prudent use.
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References1 Antimalarial Medications – StatPearls – NCBI Bookshelf2 Antimalarial medication – Wikipedia (2025-03-21)3 Quinoline antimalarials: mechanisms of action and resistance – PubMed4 Anti‐malarial drugs: Mechanisms underlying their proarrhythmic effects – British Journal of Pharmacology5 Antimalarials in Dermatology: Mechanism of Action, Indications, and … – Actas Dermo-Sifiliográficas6 Antimalarials: Function, Uses, Side Effects, Drug Names – RxList
