As mentioned in a previous blog post, the new hospital acquired pneumonia/ventilator-associated pneumonia (HAP/VAP) guidelines were recently released in July of 2016 as a joint effort between the ATS and the IDSA, in order to help assist clinicians in effectively managing patients who develop pneumonia in the nosocomial setting. Although multiple pathogens are associated with both HAP/VAP, one of the organisms most feared by both physicians and patients alike is methicillin resistant Staphylococcus aureus, or MRSA.
This presence of this organism began to steadily increase in the nosocomial setting from the 1960’s to the late 1990’s, and has made headlines as being one of the first of many ‘superbugs’ that are appearing within hospitals, nursing homes, infusion centers and other health care associated facilities.
So what do the new guidelines say about managing patients with HAP/VAP that are infected with MRSA, and what is the evidence behind these recommendations?
It may not be what you think. The panel recognizes that concerns for MRSA among patients with pneumonia has led to excessive antibiotic treatment, which in turn has led to excessive costs as well as antibiotic-associated morbidity, and even mortality not to mention the potential for the development of further antibiotic resistance among these bacteria over time. In order to minimize this, recommendations have been made to only cover for MRSA empirically under a specific set of conditions.
For VAP, MRSA coverage should only be considered if the patient has a risk factor associated with the development for antibiotic resistance (See Table), if the rate of MRSA within the medical facility where the patient is being treated is >10%, or if the rate is simply not known within the facility. If none of these criteria are met, empiric coverage for MRSA is NOT required, and treatment should be provided either with a beta-lactam or respiratory quinolone that targets methicillin susceptible isolates (MSSA).
For HAP, the recommendations are similar, except that treatment should be considered if the rate of MRSA is >20% within the facility where treatment is being provided, and empiric treatment for MRSA can be given when the patient is at high risk for mortality (defined by them as the need for ventilator support or evidence of septic shock).
So when treatment is required, which is the better drug to give, vancomycin or linezolid? According to the guidelines, both are generally considered equivalent in their efficacy. This stems from 4 studies (3 randomized controlled trials, one randomized double blinded multicenter study) comparing the two drugs with respect to efficacy in the treatment of MRSA pneumonia. Overall, no statistically significant differences were noted between the two drugs. In Wunderlick and colleagues multicenter study, linezolid did show statistically significant superiority in clinical response, however the overall 60 day mortality was still the same between those patients that received linezolid and those that received vancomycin.
However, all of this is trumped by the overwhelming theme of the current guidelines, which is that empiric treatment should be guided by antibiograms specific for the facility at which the patient is being managed for their VAP/HAP. The decision on whether to use linezolid or vancomycin should therefore be influenced by these antibiograms, along with cost and risk factors that may predispose the patient to one or more side effects of either drug.
In the end, providing antibiogram-targeted therapy for MRSA when specific risk factors are present, followed by de-escalation of therapy after susceptibility testing has returned, is the primary message outlined by the new guidelines.
PUBMED References:
Kalil, AC et al Clinical Infectious Diseases, 2016 ; 63 : 1 -51
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