**Question:** The drug of choice for chemoprophylaxis in contacts of a patient of pneumonic plague is -

A. Ciprofloxacin
B. Rifampicin
C. Acyclovir
D. Amoxicillin

**Correct Answer:** A. Ciprofloxacin

**Core Concept:**
Pneumonic plague is a severe and potentially lethal bacterial infection caused by the bacterium Yersinia pestis. Chemoprophylaxis involves the use of antibiotics to prevent the development of the infection in close contacts of a patient with pneumonic plague. The primary goal of chemoprophylaxis is to inhibit the growth and transmission of Y. pestis.

**Why the Correct Answer is Right:**
Ciprofloxacin is a broad-spectrum fluoroquinolone antibiotic that has excellent activity against Y. pestis. It demonstrates bactericidal action, inhibiting bacterial DNA replication and transcription. Given that the bacterium Y. pestis causes pneumonic plague, ciprofloxacin is the appropriate choice for chemoprophylaxis.

**Why Each Wrong Option is Incorrect:**

A. Ciprofloxacin is not an option: The correct answer is Ciprofloxacin, not Ciprofloxacin. This mistake in spelling and incorrect option make this choice wrong.

B. Rifampicin is a bacteriostatic antibiotic that inhibits bacterial DNA-dependent RNA polymerase and is primarily used for treating tuberculosis. It does not have sufficient activity against Y. pestis, making it an incorrect choice for chemoprophylaxis against pneumonic plague.

C. Acyclovir is an antiviral drug primarily used for treating herpes simplex virus infections. It has no activity against Y. pestis and is not suitable for chemoprophylaxis against pneumonic plague.

D. Amoxicillin is a penicillin antibiotic used for treating bacterial infections, but it is not active against Y. pestis. This makes it an unsuitable choice for chemoprophylaxis against pneumonic plague.

**Clinical Pearls:**
Plague is a severe and potentially life-threatening infection caused by the bacterium Yersinia pestis. Chemoprophylaxis is crucial in preventing the spread of the disease to contacts of infected individuals. The choice of antibiotic should be based on its activity against Y. pestis and its safety profile in humans. In this case, ciprofloxacin is the appropriate choice due to its excellent activity against Y. pestis and its acceptable safety profile in humans. The other options (rifampicin, acyclovir, and amoxicillin) are not effective against Y. pestis and should not be used for chemoprophylaxis in contacts of patients with pneumonic plague.