Giardiasis — DTM&H MCQ
Instant feedback + full explanation. One question, done properly.
Educational content. Not a substitute for clinical judgement or local policy.
Reveal the answer and explanation
Correct answer: D — Tinidazole or metronidazole with hydration advice
The correct answer is D, tinidazole or metronidazole with hydration advice. Giardia duodenalis is a flagellate protozoan acquired from untreated water, and its classic presentation is exactly this: bloating, foul (sulphurous) belching, and greasy, non-bloody diarrhoea from small bowel malabsorption rather than colonic invasion. Nitroimidazoles are first line because they are directly active against Giardia trophozoites, with tinidazole typically given as a single dose and metronidazole as a short multi-day course. Oral rehydration is a sensible adjunct for symptomatic fluid loss but does not clear the parasite, so specific antiprotozoal therapy is required once the diagnosis is confirmed by a positive stool antigen test. Why the other options are wrong: A. Ciprofloxacin for invasive dysentery: this stem describes malabsorptive, non-bloody diarrhoea with no evidence of mucosal invasion or bacterial dysentery, and ciprofloxacin has no activity against Giardia trophozoites. B. Praziquantel after a fatty meal: praziquantel is an anthelmintic used for trematodes and cestodes (for example schistosomiasis and tapeworms), not for a flagellate protozoan like Giardia. E. Oral rehydration without antiparasitic therapy: hydration alone does not eradicate Giardia trophozoites from the small intestine and risks prolonged carriage and ongoing malabsorptive symptoms. C. Ivermectin with repeat dosing: ivermectin targets nematodes and ectoparasites (such as Strongyloides or scabies) and has no established role or licensed indication against Giardia. Key point: confirmed giardiasis after freshwater or untreated water exposure with malabsorptive, non-bloody diarrhoea is treated with a nitroimidazole (tinidazole single dose or metronidazole course) plus supportive hydration, not antibacterials or antihelminthics.
Reference: BNF (NICE), Antiprotozoal drugs, Metronidazole and Tinidazole: Giardiasis indications and dosing, https://bnf.nice.org.uk/drugs/tinidazole/