What medication is recommended for the treatment of methicillin-sensitive Staphylococcus aureus (MSSA) infections?

Nafcillin is the preferred medication for treating methicillin-sensitive Staphylococcus aureus (MSSA) infections because it is a penicillinase-resistant antibiotic specifically designed to combat penicillin-resistant strains of Staphylococcus aureus. MSSA, by definition, is sensitive to methicillin and its derivatives, including nafcillin, making it an effective choice for such infections. Nafcillin is known for its efficacy against MSSA due to its ability to resist degradation by beta-lactamases, which are enzymes that some bacteria produce to inactivate certain antibiotics.

Other medications, while effective for different types of infections, are not typically used as first-line treatments for MSSA. Vancomycin is generally reserved for methicillin-resistant Staphylococcus aureus (MRSA) or when there's a serious infection that cannot be treated with first-line agents. Doxycycline has broad-spectrum efficacy and is useful against various infections, but it is not the first choice for MSSA specifically. Amoxicillin is more appropriate for less severe infections and is not effective against Staphylococcus aureus, especially due to the potential production of beta-lactamases. Therefore, nafcillin remains the optimal and first-line agent for treating MSSA infections.