I have an 84 year old patient with COPD that presented with a clear pneumonia on CXR. The following day his blood cultures were positive for MSSA. He was started on ceftriaxone, azithromycin and metronidazole and is doing fairly well. What is the appropriate change in antibiotic management?
S. aureus bacteremia from a pneumonia source is relatively rare so I would want to make sure it is the source. In this case it does seem quite clear, however. In general, “aiming” therapy specifically at the organism found in blood cultures is appropriate for many types of infections including pneumonia. Exceptions include obvious polymicrobial circumstances such as colon associated abscesses.
Cloxacillin in high dose is preferred. 2 grams Q6H is the standard adult high dose. Some advocate Q4H dosing for very severe circumstances. I favor cloxacillin over cefazolin because of its narrow spectrum with much less effect on GI flora and lessor propensity to induce C. difficile disease. Mono-therapy is reasonable in this setting but if concern is expressed over potential for polymicrobic infection in the context of COPD I would advocate continuing the ceftriaxone for 1 or 2 more days and then finishing a total course of therapy of 7-10 days with cloxacillin alone. Sequential therapy with oral cloxacillin may be quite appropriate.