Pharmacology of Antimalarial Drugs | Free Topic Wise Notes

Pharmacology of Antimalarial Drugs explains mechanisms and actions of drugs used to treat malaria by targeting Plasmodium.

Malaria is caused by Plasmodium species (P. falciparum, P. vivax, P. malariae, P. ovale), transmitted by the bite of female Anopheles
Antimalarial drugs are classified based on the stage of the parasite they act upon:
Tissue schizonticides: Act on liver stages
Blood schizonticides: Act on asexual blood stages
Gametocides: Destroy sexual forms to prevent transmission

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4-Aminoquinolines
- Examples: Chloroquine, Amodiaquine
- Mechanism: Inhibits heme polymerase → toxic heme accumulates → parasite death
- Use: Effective against vivax, P. ovale, and sensitive P. falciparum
- Adverse Effects: Retinopathy, pruritus, GI upset
- Note: Resistance common in falciparum
Artemisinin Derivatives
- Examples: Artesunate, Artemether, Dihydroartemisinin
- Mechanism: Generates free radicals → damages parasite proteins
- Use: First-line for severe or resistant falciparum malaria (always in combination = ACT)
- Note: Very rapid action, short half-life
Quinoline Methanols
- Example: Quinine
- Use: Severe malaria (especially multidrug-resistant)
- Adverse Effects: Cinchonism (tinnitus, headache), hypoglycemia, cardiac effects
Antifolates
- Examples: Pyrimethamine + Sulfadoxine (Fansidar)
- Mechanism: Inhibit folate synthesis in parasites
- Use: Not used alone due to resistance
- Note: Commonly used as prophylaxis or in combination
Atovaquone + Proguanil
- Mechanism: Mitochondrial inhibition (atovaquone), folate antagonist (proguanil)
- Use: Prophylaxis and treatment of falciparum malaria
Primaquine
- Mechanism: Tissue schizonticide and gametocide
- Use: Radical cure of vivax and P. ovale (kills hypnozoites)
- Caution: Contraindicated in G6PD deficiency → risk of hemolysis

Phase	Key Features
Absorption	Mostly oral; absorption varies with food. Artemisinin has poor oral bioavailability, so sometimes given IV or rectally.
Distribution	Accumulates in liver, spleen, and RBCs. Tissue binding and protein binding vary by drug.
Metabolism	Most metabolized in the liver. For example, chloroquine undergoes hepatic metabolism. CYP enzymes may be involved.
Excretion	Mostly renal (e.g., chloroquine, quinine) or biliary. Long half-life drugs can accumulate and cause toxicity.
Drug Interactions	Enzyme inducers/inhibitors may affect levels. QT prolongation is additive with other drugs that affect cardiac rhythm.