Adverse reactions to methicillin and nafcillin during treatment of serious Staphylococcus aureaus infections.

Relative toxicities of methicillin and nafcillin were compared in 70 patients with serious infections caused by Staphylococcus aureus. Of the 29 patients treated with nafcillin, four had fever, rash, and leukopenia and 1 had absolute neutropenia. Of the 41 patients treated with methicillin, 16 experienced 27 reactions. In addition to fever and skin rash, neutropenia and urinary tract abnormalities were common. Methicillin and nafcillin are equally effective in treating S aureus infections, but methicillin was significantly and more frequently associated with adverse drug reaction that was nafcillin.