Which is not cysticidal for entamoeba –
**Core Concept**
Entamoeba histolytica is a protozoan parasite that causes amoebiasis. Cysticidal agents are used to kill the cyst form of the parasite, which is responsible for transmission and reinfection. Effective cysticidal agents are crucial in the treatment of amoebiasis.
**Why the Correct Answer is Right**
Metronidazole is a commonly used antibiotic that acts on the trophozoite form of Entamoeba histolytica, inhibiting DNA synthesis and causing cell death. However, it is not cysticidal, meaning it does not kill the cyst form of the parasite. This is because the cyst form is encysted and dormant, making it resistant to the effects of metronidazole.
**Why Each Wrong Option is Incorrect**
**Option A:** Paromomycin is an aminoglycoside antibiotic that is known for its cysticidal activity against Entamoeba histolytica. It works by inhibiting protein synthesis in the cyst form, ultimately leading to its death.
**Option B:** Iodoquinol is a halogenated acridine derivative that has been shown to have cysticidal activity against Entamoeba histolytica. It works by disrupting the cyst membrane and ultimately leading to its death.
**Option C:** Diloxanide furoate is an anthelmintic that has been used to treat amoebiasis. It has been shown to have cysticidal activity against Entamoeba histolytica, making it an effective treatment option.
**Clinical Pearl / High-Yield Fact**
It is essential to note that metronidazole is not sufficient as a single treatment for amoebiasis, as it does not kill the cyst form of the parasite. A combination of metronidazole with a cysticidal agent such as paromomycin or iodoquinol is recommended for effective treatment.
**Correct Answer: D. Metronidazole**