Which antibiotic is commonly used with amoxicillin for synergy in endocarditis therapy?

• A. Gentamicin
• B. Vancomycin
• C. Ceftriaxone
• D. Azithromycin

Answer: (A)

Synergy in endocarditis therapy comes from pairing a cell-wall–active antibiotic with an aminoglycoside to achieve greater bacterial killing than either would alone. Amoxicillin disrupts the bacterial cell wall, which allows the aminoglycoside to enter the bacteria more effectively and inhibit protein synthesis. This combined action produces a stronger, faster kill, especially for Enterococcus species and certain viridans group streptococci that cause endocarditis.

Gentamicin is the antibiotic that is commonly used with amoxicillin for this purpose because it is an aminoglycoside that leverages that increased intracellular access to enhance bactericidal activity. This synergy is particularly important in enterococcal endocarditis, where the dual attack improves outcomes.

Other drugs listed don’t provide the same established synergy with amoxicillin in endocarditis. Vancomycin is used for resistant Gram-positive infections but isn’t chosen specifically for synergy with amoxicillin in this context. Ceftriaxone can be used in other regimens for certain streptococcal endocarditis, but it isn’t the standard partner for amoxicillin synergy. Azithromycin isn’t suitable for endocarditis therapy due to limited bactericidal activity against the common pathogens.