**Question:** Drug not used in candidiasis -

A. Amphotericin B
B. Fluconazole
C. Nystatin
D. Fluorouracil

**Correct Answer:** D. Fluorouracil

**Core Concept:**
Candidiasis is a group of infections caused by the fungus Candida, which is a normal commensal in the human gastrointestinal and genitourinary tracts. Treatment options vary depending on the type and severity of the infection.

**Why the Correct Answer is Right:**
Fluorouracil (5-FU) is an antimetabolite used in the treatment of various cancers, including colorectal, pancreatic, and breast cancer. It interferes with DNA and RNA synthesis in rapidly dividing cells, leading to cell death. However, Candida is a yeast cell, which does not divide rapidly. Therefore, fluorouracil is not effective against Candida infections.

**Why Each Wrong Option is Incorrect:**

A. Amphotericin B: A polyene antifungal medication, effective against various fungal infections, including candidiasis.
B. Fluconazole: A broad-spectrum azole antifungal drug, commonly used in the treatment of candidiasis.
C. Nystatin: A polyene antifungal medication, effective against various fungal infections, including candidiasis.

**Why D is Incorrect:**
Fluorouracil is not an antifungal medication, but a chemotherapeutic agent used in cancer treatment. Candidiasis is a fungal infection, and using a cytotoxic drug like fluorouracil will not effectively target and eradicate the fungal pathogen.

**Clinical Pearl:**
When treating candidiasis, it is essential to select appropriate antifungal agents that target fungal cells, rather than cytotoxic drugs like fluorouracil, to ensure effective treatment and minimize harm to the patient's healthy cells.