A 40-year-old man with amoebic liver abscess completes a full course of metronidazole with resolution of fever and shrinkage of the abscess. His stool examination remains positive for Entamoeba histolytica cysts. The reason a second drug is required is:
- A Metronidazole is active against trophozoites in tissues but poorly effective against cysts in the intestinal lumen ✓
- B Metronidazole achieves poor tissue concentrations in the liver
- C Metronidazole induces enzymes that convert cysts into resistant trophozoites
- D Metronidazole requires concomitant chloroquine to achieve luminal activity
Correct answer: A. Metronidazole is active against trophozoites in tissues but poorly effective against cysts in the intestinal lumen
Explanation
Metronidazole is highly effective against invasive trophozoites in the intestinal wall and liver, which explains its dramatic response in amoebic liver abscess, but it achieves inadequate luminal concentrations and fails to eradicate encysted organisms in the gut lumen. B luminal amoebicide such as diloxanide furoate or paromomycin must follow to eliminate cysts and prevent relapse and transmission. Tissue penetration is excellent, so option B contradicts the clinical response seen here.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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