A female patient was treated with antibiotics for chlamydia induced UTI, suddenly presents again with itching/pruritus, vaginal discharge, burning micturition. Which drug should be given?

**Core Concept**
The patient's symptoms suggest a case of antibiotic-associated pseudomembranous colitis caused by Clostridioides difficile (C. diff), a common complication of broad-spectrum antibiotic therapy for bacterial infections like chlamydia-induced UTI. The underlying principle being tested is the need for specific treatment of C. diff infection to prevent further complications.

**Why the Correct Answer is Right**
The patient's symptoms of itching/pruritus, vaginal discharge, and burning micturition, along with a recent history of antibiotic use, suggest a diagnosis of pseudomembranous colitis. The correct treatment for C. diff infection is metronidazole (Flagyl), which works by inhibiting DNA synthesis in the bacteria, ultimately leading to cell death. Metronidazole is effective against C. diff due to its ability to penetrate the bacterial cell membrane and interact with the DNA, causing damage to the bacterial genome.

**Why Each Wrong Option is Incorrect**
**Option A:** Vancomycin is an antibiotic used to treat C. diff infection, but it is typically administered orally in a pill form or rectally as a suppository, making it less suitable for this scenario. Vancomycin is not the first-line treatment for C. diff infection.
**Option B:** Fluconazole is an antifungal medication used to treat fungal infections, which is not relevant to this case of pseudomembranous colitis caused by C. diff.
**Option C:** Ciprofloxacin is a broad-spectrum antibiotic that may have contributed to the development of C. diff infection, but it is not the treatment for the infection itself.

**Clinical Pearl / High-Yield Fact**
When treating patients with broad-spectrum antibiotics, it's essential to consider the risk of C. diff infection and monitor for symptoms such as diarrhea, abdominal pain, and blood in stool. Early identification and treatment of C. diff infection can prevent complications and improve patient outcomes.

**Correct Answer:** A. Metronidazole (Flagyl)