Vancomycin efficacy (MIC and Bactericidality) in Clinical Outcome in Patients with Methicillin Resistant Staphylococcus Aureus (MRSA) Bacteraemia

Mahableshwar S Albur, Alan Noel, Sharon Tomaselli, Karen Bowker, Andrew Lovering, Elizabeth Darley, Alasdair P MacGowan

Research output: Contribution to conferenceConference Abstractpeer-review

Abstract

Background: MRSA is a major cause of hospital-and community-acquired bacteraemia and is associated high mortality. Vancomycin susceptibility against MRSA is decreasing over time and in ways that are difficult to detect by routine laboratory methods. In this study we attempted to determine various factors affecting the clinical outcome of MRSA bacteraemia and any influence of vancomycin MIC and cidality on it.

Methodology: 35 MRSA isolates from 38 patients (3 isolates missing) with MRSA bacteraemia were used for vancomycin susceptibility testing by agar dilution method, and cidality was determined in brain heart infusion broth containing vancomycin (16 μg/ml). Retrospective case notes review was done to determine the clinical variables including demography, co-morbidity, prognosis of underlying disease estimated by McCabe-Jackson score (MJS), source of bacteraemia, prior use of vancomycin, treatment data, vancomycin assay results, and clinical outcomes at 1month.

Results: Of the 38 patients, 9(24%) were community-and 28(76%) health-care acquired. Mean age was 71 years. Majority of them 24(64%) had significant renal failure and 13(34%) were on hemodialysis. Other co-morbidities included Diabetes (10/38), COPD (5/38), Malignancy (4/38) and miscellaneous (20/38). Life-expectancy due to underlying co-morbidities estimated by MJS was ultimately-fatal (life-expectancy 3months-5years) in 28(74%) and non-fatal (life-expectancy >5years) in 9(24%). At 1 month, 9(24%) were discharged home, 12(32%) still in-patient, and 16(44%) died. The mean vancomycin MIC was 0.66, 0.77, and 0.71 respectively, suggesting a trend towards better outcome with lower MIC. However, this was not reflected in the cidality of vancomycin over 72 hours (measured as log 10 drop) 7.6991 ± 0.5995, 7.6924 ± 0.5027, 7.4871 ± 0.4680 respectively. Isolates from patients who had received vancomycin within the preceding month (9 out of 38) had a higher MIC (0.75 versus 0.71) and a decreased cidality at 72 hours (7.5159 versus 7.6448)
Conclusion: In our cohort of patients with MRSA bacteraemia, the adverse clinical outcome was associated underlying co-morbid conditions. Although the increasing vancomycin MICs (well within the susceptible range) was associated with an adverse clinical outcome, but the cidality of vancomycin remained unaffected. Hence their influence on outcome is debatable. Previous vancomycin exposure increased the MIC and decreased the susceptibility to vancomycin.
Original languageEnglish
Publication statusPublished - 30 Nov 2008
EventFederation of Infection Societies 2008 - Cardiff, United Kingdom
Duration: 29 Nov 20081 Dec 2008

Conference

ConferenceFederation of Infection Societies 2008
CountryUnited Kingdom
CityCardiff
Period29/11/081/12/08

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