Malaria is a serious parasitic disease caused by Plasmodium species (P. vivax, P. falciparum, P. malariae, P. ovale, and P. knowlesi). The infection spreads through the bite of infected female Anopheles mosquitoes. Anti-malarial drugs are used to prevent or treat malaria by killing the parasite at different stages of its life cycle.
Malaria Life Cycle – In Brief
The malaria parasite has two main stages:
- Liver stage (exo-erythrocytic) – Parasites multiply inside liver cells.
- Blood stage (erythrocytic) – Parasites infect red blood cells causing fever and other symptoms.
Some drugs act in the liver stage, while others target the blood stage.
Classification of Anti-Malarial Drugs
1. Blood Schizonticides (act on RBC stage)
- Chloroquine
- Quinine
- Mefloquine
- Artemisinin derivatives (Artesunate, Artemether)
- Pyrimethamine + Sulfadoxine
2. Tissue Schizonticides (act on liver stage)
- Primaquine
- Tafenoquine
3. Gametocytocides (block transmission to mosquito)
- Primaquine
- Artemisinin derivatives
4. Prophylactic Agents
- Chloroquine (in sensitive areas)
- Mefloquine
- Doxycycline
Major Anti-Malarial Drug Profiles
1) Chloroquine
Mechanism: Inhibits heme detoxification in the parasite, causing toxic buildup and death.
Uses: Effective for sensitive P. vivax and P. malariae. Not effective where resistance exists (many regions).
Side effects: Itching, GI upset, rare retinal toxicity.
2) Quinine
Mechanism: Interferes with parasite DNA and protein synthesis.
Uses: Severe malaria and chloroquine-resistant P. falciparum.
Side effects: Cinchonism (tinnitus, dizziness), hypoglycemia.
3) Artemisinin and Derivatives
- Artemether
- Artesunate
- Dihydroartemisinin
Mechanism: Produces free radicals inside the parasite, damaging vital proteins.
Use: First-line therapy for P. falciparum malaria in combination regimens (ACT – Artemisinin Combination Therapy).
4) Mefloquine
Use: Treatment and prevention of chloroquine-resistant malaria.
Side effects: Neuropsychiatric effects (nightmares, anxiety), not for people with mental health issues.
5) Primaquine
Mechanism: Acts on dormant liver forms (hypnozoites) of P. vivax and P. ovale.
Use: Radical cure to prevent relapse.
Important: Must test for G6PD deficiency due to risk of hemolysis.
6) Pyrimethamine + Sulfadoxine (Fansidar)
Mechanism: Sequential blockade of folate synthesis in the parasite.
Use: Alternative drug for resistant malaria.
7) Atovaquone + Proguanil
Use: Treatment and prophylaxis of malaria.
Mechanism: Atovaquone inhibits mitochondrial function; proguanil enhances activity.
8) Doxycycline
Used as a prophylactic agent in travelers.
Mechanism: Inhibits protein synthesis in the parasite.
Treatment Guidelines (General Concepts)
Choice of anti-malarial therapy depends on:
- Type of Plasmodium species
- Geographical drug resistance patterns
- Patient age, pregnancy status, and severity of disease
For P. vivax and P. ovale
- Chloroquine (if sensitive) for blood stages
- Primaquine or Tafenoquine for liver hypnozoites (prevent relapse)
For P. falciparum
- Artemisinin-based combination therapy (ACT)
- Quinine (in severe cases)
Side Effects of Anti-Malarials
- GI disturbances
- Headache and dizziness
- Retinopathy (with long-term chloroquine use)
- Hypoglycemia with quinine
- Hemolysis in G6PD-deficient patients (with primaquine)
Detailed Notes:
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