Which antibiotics are specifically effective against anaerobes in abdominal infections?

Metronidazole is particularly effective against anaerobes and is frequently used to treat abdominal infections that involve anaerobic bacteria. This antibiotic works by disrupting the DNA synthesis of anaerobic organisms, making it effective in treating infections caused by bacteria such as Bacteroides fragilis, which is commonly involved in intra-abdominal infections.

Clindamycin also has efficacy against anaerobes and can be used for similar infections. However, metronidazole is often preferred for its specific action against anaerobic bacteria, particularly in the context of gastrointestinal tract infections.

Vancomycin primarily targets gram-positive bacteria, particularly Staphylococcus aureus and Streptococcus species, thus it does not have significant activity against anaerobes.

Gentamicin is an aminoglycoside antibiotic mainly effective against aerobic gram-negative bacteria and has no efficacy against anaerobes.

Given these characteristics, metronidazole is the most appropriate choice for effective treatment against anaerobic bacteria in abdominal infections.