Failure of a once-daily regimen of cefonicid for treatment of endocarditis due to Staphylococcus aureus.

Cefonicid, a new long-acting cephalosporin, was evaluated for treatment of endocarditis due to Staphylococcus aureus. Four patients, all with infection of the tricuspid valve, were treated with a single daily injection. By the fifth day of therapy, three of the four patients continued to have spiking fevers and positive blood cultures, and treatment with cefonicid was discontinued. Even though peak concentrations of antibiotic in serum were greater than 20-40 times the minimum inhibitory concentration of the antibiotic for the infecting organism, serum bactericidal titers were less than 1:8 in three patients. Susceptibility testing of 52 clinical isolates in broth confirmed a marked difference between inhibitory and bactericidal concentrations for 40% of these strains. In addition, susceptibility testing performed in serum rather than broth resulted in a sixfold increase in the minimum inhibitory concentration, a result suggesting that protein binding may be in part responsible for these failures of treatment. Cefonicid administered as a single daily dose is inadequate for treatment of endocarditis due to S. aureus and should not be used for treatment of bacteremia or life-threatening infections known or suspected to be caused by this organism.