Treat Methicillin-Resistant Staphylococcus Aureus with a Minimum of 14 days of Antibiotics
Iosifina Giannakikou MD
There are approximately 2 million nosocomial infections in the United States each year. About 30% of these infections are by Staphylococcus aureus, of which 40% are methicillin-resistant S. aureus (MRSA). In intensive care units (ICUs), the percentage of antibiotic-resistant Staph infections approaches 60%. The major reservoir of MRSA in institutions is colonized and infected inpatients. Nasal carriage of MRSA in ICU patients was associated with an MRSA bacteraemia rate of 38%, four times higher than methicillin-sensitive S. aureus. One-third of colonized patients become infected and one-half of these have pneumonia or bloodstream infection. Mortality rates for nosocomial-acquired MRSA infections may reach 50% for bloodstream infections and 33% for pneumonia.
What to Do
Vancomycin (a glycopeptide) is the standard treatment for MRSA. Vancomycin 15 mg/kg q 12h, or usually 1g qd, is administered intravenously for 14 to 21 days. Recent randomized control studies have shown linezolid to be as efficacious as vancomycin and with a predictable bacteriostatic activity for suspected or proven MRSA infections. Linezolid, an oxazolidinone antibiotic, is available in an intravenous and an oral form, which is 100% bioavailable. Linezolid’s dose is 600 mg intravenously or orally (IV/PO) q 12h. However, vancomycin is still preferred by some authorities in order to increase longevity of linezolid’s activity. In Europe, teicoplanin (also a glycopeptide) is commonly used.
In cases of vancomycin-treatment failure or allergy, other drugs used for treating MRSA bacteremia are quinupristin-dalfopristin, 7.5 mg/kg IV q12h and daptomycin, 6 mg/kg IV qd.
MRSA bacteremia should be treated with at least a 14-day course of antibiotics if there is prompt (within 72 hours) clinical response. If there is persistent bacteremia (more than 3 days), some advocate 4 weeks of treatment even with a negative echocardiogram. In the case of endocarditis, the treatment course should increase to at least
6 weeks. Recurrence or relapse rates are high if patients are treated for less than the suggested course.
6 weeks. Recurrence or relapse rates are high if patients are treated for less than the suggested course.
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