**Question:** Prophylaxis for anthrax

**Core Concept:** Anthrax is a severe infectious disease caused by the bacterium Bacillus anthracis. Prophylactic antibiotics are used to prevent the infection in high-risk individuals, such as those handling contaminated animal hides or wool.

**Why the Correct Answer is Right:**

Correct Answer: C. Doxycycline

Prophylactic antibiotics for anthrax primarily target the bacterium Bacillus anthracis. Doxycycline is a tetracycline antibiotic with broad-spectrum activity against gram-positive and some gram-negative bacteria, including Bacillus anthracis. It inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing peptide bond formation. This makes doxycycline an effective choice for anthrax prophylaxis.

**Why Each Wrong Option is Incorrect:**

A. Penicillin: Penicillin is a beta-lactam antibiotic with limited activity against gram-positive bacteria, unlike doxycycline. Additionally, Bacillus anthracis is resistant to penicillin due to its thick cell wall.

B. Ciprofloxacin: Ciprofloxacin belongs to the quinolone class and is effective against gram-negative bacteria but not as effective against gram-positive bacteria like Bacillus anthracis.

D. Metronidazole: Metronidazole is a nitroimidazole antibiotic primarily active against anaerobic bacteria. It lacks activity against gram-positive bacteria like Bacillus anthracis.

**Clinical Pearl:** Prophylactic antibiotics for anthrax are essential to neutralize the risk of infection in high-risk individuals, ensuring early treatment if exposure occurs. Prompt antibiotic administration is crucial in preventing the development of severe disease and its complications.