Which of the following is a drug that can be used for prophylaxis after exposure to N. meningitidis?

Rifampin is the recommended drug for prophylaxis after exposure to Neisseria meningitidis, also known as meningococcal bacteria. This antibiotic is effective in eradicating the nasopharyngeal carriage of the organism in individuals who have been in close contact with a person diagnosed with meningococcal disease. The ability of rifampin to reduce the risk of infection is especially crucial in outbreak situations or for people who have had close contact with an infected individual, as it helps to prevent the bacteria from spreading within the community.

In contrast, the other options do not serve this specific prophylactic purpose against N. meningitidis. Ciprofloxacin, while it can be used as an alternative for prophylaxis, is not the primary recommendation or the most common drug used in this context. Ethambutol and metronidazole have different indications and are not effective against meningococcal bacteria, making them unsuitable for prophylactic measures in this case. Understanding the specific roles of these antimicrobials is essential for effective management of potential meningococcal exposure.