**Question:** Mebendazole cannot be used for:

A. Schistosomiasis
B. Malaria
C. Trypanosomiasis
D. Giardiasis

**Core Concept:** Mebendazole is an antiparasitic drug used for treating infections caused by various parasites, particularly helminths (infections involving worms). It belongs to a class of drugs known as benzimidazoles.

**Why the Correct Answer is Right:** Mebendazole is primarily effective against parasites, not bacteria or viruses. The correct answer, B (Malaria), is ruled out because malaria is caused by protozoan parasites of the Plasmodium species, and mebendazole is not effective against them.

**Why Each Wrong Option is Incorrect:**

A. Schistosomiasis: Meant by Schistosomiasis is caused by Schistosoma species of trematode worms. Although mebendazole is effective against some trematodes, Schistosoma worms are not targeted, making option A incorrect.

C. Trypanosomiasis: Trypanosomiasis is caused by Trypanosoma species, which are protozoan parasites, not typical targets for mebendazole.

D. Giardiasis: Giardiasis is caused by Giardia duodenalis (also known as Giardia lamblia or Giardia intestinalis), a protozoan parasite. Mebendazole is effective against some protozoan parasites, but not Giardia, making option D incorrect.

**Clinical Pearl:** Mebendazole is a valuable tool in treating various parasitic infections, but its effectiveness is limited to specific parasites. Understanding its scope helps in selecting the appropriate antiparasitic drug for treating various parasitic diseases. Always consider consulting a medical expert or referring to a reliable medical reference when determining the appropriate therapy for a patient's condition.