Question

A 45-year-old with chronic diarrhoea and abdominal discomfort; stool examination reveals larvae of Strongyloides stercoralis. Which is the preferred drug for treatment?

• A. Nitazoxanide
• B. Metronidazole
• C. Paromomycin
• D. Ivermectin

Hint:

Strongyloides is a roundworm, and the drug of choice is the macrocyclic lactone anthelmintic.

Answer 1

The Correct Option is D

Step 1: Understand the clinical picture:
The patient has chronic diarrhoea and abdominal discomfort, and the stool shows larvae of Strongyloides stercoralis. This is strongyloidiasis, an intestinal infection caused by a threadworm (a small roundworm).
The infective filariform larvae enter through the skin of the feet. They travel through the lungs to the small intestine, where the adult female lives in the mucosa.
The eggs hatch inside the gut, so rhabditiform larvae appear in the stool. Some of them turn into infective larvae within the same person (autoinfection), so the infection can last for years.

Step 2: Recall why treatment is important:
In people on steroids or with weak immunity, the larvae multiply fast. This causes hyperinfection and disseminated disease with a high death rate.
So every proven case needs full treatment with a drug that kills the larvae and the adult worms.

Step 3: Recall the drug of choice:
The preferred drug for strongyloidiasis is ivermectin. The usual dose is 200 micrograms per kg once a day, given for 1 to 2 days.
Ivermectin binds to glutamate-gated chloride channels in the nerve and muscle cells of the worm. Chloride rushes in, the cell membrane becomes hyperpolarised, and the worm is paralysed and expelled.
Albendazole is only an alternative, because its cure rate is lower. So option (D) is the best choice.

Step 4: Check option (A) Nitazoxanide:
Nitazoxanide blocks the pyruvate-ferredoxin oxidoreductase enzyme of anaerobic organisms. It is used mainly for Giardia and Cryptosporidium diarrhoea.
It is not the preferred drug for Strongyloides. So (A) is wrong.

Step 5: Check option (B) Metronidazole:
Metronidazole is a nitroimidazole. It works against anaerobic bacteria and protozoa such as Entamoeba histolytica, Giardia and Trichomonas.
It has no useful action on nematodes (roundworms). So (B) is wrong.

Step 6: Check option (C) Paromomycin:
Paromomycin is an aminoglycoside that is hardly absorbed from the gut. It is used as a luminal amoebicide and for Cryptosporidium in some cases.
It does not kill Strongyloides larvae. So (C) is wrong.

Final Answer:
The preferred drug for intestinal strongyloidiasis is ivermectin. This is option (D).