**Core Concept**
Infected pancreatic necrosis is a severe complication of acute pancreatitis, characterized by necrosis of pancreatic tissue infected by bacteria. Management involves antimicrobial therapy, supportive care, and sometimes surgical intervention to debride the infected tissue.

**Why the Correct Answer is Right**
The treatment of infected pancreatic necrosis often involves the use of broad-spectrum antibiotics to cover a wide range of pathogens. **Metronidazole** is a key antibiotic used in the treatment of infected pancreatic necrosis, particularly for its efficacy against anaerobic bacteria, which are commonly involved in this condition. Additionally, **imipenem** or **meropenem** may be used for their broad-spectrum coverage against both aerobic and anaerobic bacteria. Supportive care, including fluid resuscitation, nutritional support, and close monitoring, is also crucial in managing infected pancreatic necrosis.

**Why Each Wrong Option is Incorrect**
**Option A:** **Ciprofloxacin** is a broad-spectrum antibiotic but is not the first-line choice for treating infected pancreatic necrosis due to its limited coverage against anaerobic bacteria.
**Option B:** **Gentamicin** is an aminoglycoside antibiotic with broad-spectrum activity but is not typically used as a first-line treatment for infected pancreatic necrosis due to its nephrotoxicity and ototoxicity.
**Option C:** **Colistin** is a polymyxin antibiotic used for multidrug-resistant Gram-negative infections but is not commonly used for treating infected pancreatic necrosis.

**Clinical Pearl / High-Yield Fact**
In managing infected pancreatic necrosis, early initiation of antimicrobial therapy and supportive care is crucial to reduce morbidity and mortality. A high index of suspicion for infected pancreatic necrosis is essential in patients with acute pancreatitis, especially those with worsening clinical condition or evidence of sepsis.

**Correct Answer: D. Imipenem.**