Which of the following is a prophylaxis antibiotic?

Amoxicillin is commonly used as a prophylactic antibiotic, especially in dental procedures to prevent infective endocarditis in at-risk patients. Its ability to target a broad range of bacteria makes it a suitable choice for prophylactic measures. In particular, it is effective against the types of bacteria that are likely to enter the bloodstream during dental work, such as those from the oral cavity.

While other antibiotics in the list serve various purposes, they are not typically classified as prophylactic agents in the same context. Ciprofloxacin is primarily used for treating urinary tract infections and certain respiratory infections; Metronidazole is effective against anaerobic bacteria and protozoa, primarily used for treating infections like bacterial vaginosis or C. difficile; and Vancomycin is generally reserved for serious infections caused by Gram-positive bacteria, particularly in a hospital setting. Thus, amoxicillin stands out as the most relevant antibiotic for prophylactic use among the options provided.