Antiparasitic drugs (antiprotozoals)

Antimalarials - The Plasmodium Problem

• Blood Schizonticides: Target erythrocytic stage.
  • Chloroquine: For sensitive species (P. malariae, P. knowlesi). Inhibits heme polymerase.
  • Artemisinins (Artemether, Artesunate): Standard of care for P. falciparum, often in combination (ACT). Generate free radicals.
  • Atovaquone-Proguanil: For treatment & prophylaxis. Inhibits mitochondrial electron transport.
• Tissue Schizonticides: Target dormant liver hypnozoites.
  • Primaquine: Eradicates P. vivax & P. ovale liver forms. ⚠️ Must test for G6PD deficiency → risk of severe hemolysis.

⭐ Tafenoquine is a newer, single-dose alternative to primaquine for radical cure of P. vivax, also requiring G6PD screening.

Metronidazole & Co - Anaerobe Annihilators

• Mechanism: Prodrug activated by anaerobes → forms cytotoxic free radicals → DNA damage & cell death.
• Spectrum: Anaerobic bacteria & protozoa.
  • 📌 GET on the Metro: Giardia, Entamoeba, Trichomonas. Also covers Gardnerella vaginalis.
  • Anaerobes: Bacteroides fragilis, Clostridioides difficile (alternative to vancomycin), Fusobacterium.
• Clinical Uses:
  • Protozoal infections (trichomoniasis, giardiasis, amebiasis).
  • Anaerobic bacterial infections (e.g., aspiration pneumonia, intra-abdominal abscesses).
  • Pseudomembranous colitis (C. diff).
• Adverse Effects:
  • Disulfiram-like reaction with alcohol (flushing, tachycardia, nausea).
  • Neurotoxicity (seizures, peripheral neuropathy) with prolonged use.
  • Metallic taste.

⭐ High-Yield: Avoid alcohol during and for 3 days after metronidazole therapy to prevent a severe disulfiram-like reaction.

Other Protozoa Poisons - The Eclectic Evictors

• Nitazoxanide
  • MOA: Inhibits the pyruvate:ferredoxin oxidoreductase (PFOR) enzyme pathway, crucial for anaerobic energy metabolism.
  • Use: Giardia lamblia & Cryptosporidium parvum.
• Sodium Stibogluconate
  • Use: Leishmaniasis (cutaneous & visceral).
  • AE: Cardiotoxicity (QT prolongation), pancreatitis, elevated liver enzymes.
• Suramin & Melarsoprol (for African Trypanosomiasis)
  • Suramin: For early-stage (hemolymphatic) infection. Does not cross BBB.
  • Melarsoprol: For late-stage (CNS) infection. An arsenic compound.

  ⭐ Melarsoprol is highly toxic, causing a fatal reactive encephalopathy in 5-10% of patients. Remember it "messes with your melon."

• Pentamidine
  • Use: Pneumocystis jirovecii pneumonia (PJP), African trypanosomiasis.

High‑Yield Points - ⚡ Biggest Takeaways

• Metronidazole is first-line for Giardia, Entamoeba, and Trichomonas; causes a disulfiram-like reaction with alcohol.
• Chloroquine, for malaria, blocks heme polymerase; watch for retinal toxicity with long-term use.
• For chloroquine-resistant malaria, use mefloquine (neuropsychiatric effects) or atovaquone-proguanil.
• Artesunate is the treatment of choice for severe P. falciparum malaria.
• Treat toxoplasmosis with the combination of pyrimethamine and sulfadiazine.
• Nifurtimox is a key treatment for Chagas disease (Trypanosoma cruzi).