Which IV antibiotic is NOT used for treating MRSA?

Amoxicillin is the correct choice because it is a penicillin antibiotic that is not effective against methicillin-resistant Staphylococcus aureus (MRSA). MRSA has acquired resistance to many beta-lactam antibiotics, including those in the penicillin class, rendering amoxicillin ineffective for treating infections caused by this particular strain of bacteria.

In contrast, vancomycin and daptomycin are specifically used for treating serious MRSA infections. Vancomycin works by inhibiting cell wall synthesis in the bacteria, while daptomycin disrupts bacterial cell membranes. Tigecycline, although a tetracycline derivative, is also active against MRSA and can be used in certain situations where MRSA is present. Therefore, both vancomycin and daptomycin, along with tigecycline, remain viable treatment options against MRSA infections, which clearly distinguishes amoxicillin as unsuitable for this purpose.