Nafcillin sodium is a narrow-spectrum,[1] second-generation beta-lactam antibiotic[2] of the penicillin class.

Nafcillin is considered therapeutically equivalent to oxacillin, although one retrospective study found greater rates of hypokalemia and acute kidney injury in patients taking nafcillin compared to patients taking oxacillin.

[4] U.S. clinical practice guidelines recommend either nafcillin or oxacillin as the first-line treatment of choice for staphylococcal endocarditis in patients without artificial heart valves.

[citation needed] Milder side-effects include: There is evidence that nafcillin induces cytochrome P-450 enzymes, specifically CYP2C9.

It would be prudent to avoid this medication if there were a concern for a congestive heart failure or kidney disease.