The effect of vancomycin MIC on the treatment of bacteremia caused by methicillin-resistant strains of Staphylococcus aureus

The ineffectiveness of vancomycin treatment for bacteremia caused by strains of Staphylococcus aureus resistant to methicillin (MRSA) is unfortunately not very rare at present, and even in cases where the MRSA strain is sensitive to vancomycin.

The aim of the study, led by Spanish scientists, was to determine the effect of vancomycin BMD on the death rate from bacteremia caused by MRSA. Infectious Diseases Hospital of Barcelona Hospital analyzed 414 cases of bacteremia caused by MRSA between 1991 and 2005 using E tests to determine vancomycin BMD.

Depending on the BMD value of vancomycin, the patients were divided into 4 groups: (1) empirical vancomycin and BMD = 1 μg / ml (38 cases), (2) empirical vancomycin and BMD = 1.5 μg / ml (n = 90), (3) empirical administration of vancomycin and BMD = 2 μg / ml (n = 40) and (4) inadequate empirical therapy and BMD = 2 μg / ml (n = 246). Clinical variables considered during the study included age, concomitant diseases, previous administration of vancomycin, use of glucocorticoids, prognosis of the underlying disease, source of bacteremia, need ventilation, presence of shock and death rates.

It was found that cases of bacteremia caused by strains of MRSA with a vancomycin MIC value of 2 μg / ml were independently associated with a lower risk of shock (relative risk (RR) 0.33, CI at 95% 0.15-0.75). Shock cases were noted in 28.4%, 19.9% and 10.8% of cases with BMD strains of 1 μg / ml, 1.5 μg / ml and 2 μg / ml, respectively (p = 0.007).

On the basis of a multivariate analysis, the main prognostic factors of death have been identified:

The sources of bacteremia, in which the risk of fatal outcome is considered moderate (10-20%), have been revealed to be bone joint and soft tissue infections, and a high risk of fatal outcome (more than 20%) is observed with bacteremia against SVC infections, weaker respiratory tract, abdominal cavity, central nervous system.

Researchers conclude that mortality associated with MRSA bacteremia is significantly higher when empirically prescribing irrational antibiotics and when vancomycin has been empirically prescribed to treat infections caused by MRSA strains with values of MIC of vancomycin greater than 1 μg / ml. In addition, the authors note that studies are needed to identify the benefits of new antistaphylococcal drugs, such as linezolid, daptomycin, tigecycline or dalbavancin, in the presence of an infection caused by strains of MRSA with vancomycin IPC greater than 1 μg / ml.