A patient with amoebic liver abscess responds to metronidazole but symptoms recur after completion of the tissue amoebicidal course. Which drug is added as a luminal amoebicide to eradicate intestinal cyst carriage, and what is its mechanism?
- A Paromomycin; non-absorbed aminoglycoside that acts luminally on cysts by inhibiting protein synthesis ✓
- B Tinidazole; it is active against both trophozoites and cysts
- C Diloxanide furoate; it directly kills trophozoites in the lumen
- D Chloroquine; it accumulates in the intestinal lumen at high concentrations
Correct answer: A. Paromomycin; non-absorbed aminoglycoside that acts luminally on cysts by inhibiting protein synthesis
Explanation
Metronidazole kills tissue trophozoites but has poor activity against cysts in the intestinal lumen, so patients are given a luminal agent to prevent relapse and transmission. Paromomycin is a non-absorbed aminoglycoside given orally that acts locally in the gut lumen to kill cysts by inhibiting protozoal ribosomal protein synthesis. Diloxanide furoate is an alternative luminal agent but the mechanism description in C is imprecise. Tinidazole is like metronidazole and also fails as a luminal agent.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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