Relationship between the MIC of vancomycin and clinical outcome in patients with MRSA nosocomial pneumonia.
OBJECTIVE
The objective of this study is to assess the distribution of vancomycin minimum inhibitory concentrations (MICs) in methicillin-resistant Staphylococcus aureus (MRSA) isolates and evaluate the efficacy of vancomycin relative to vancomycin MICs in adult patients with MRSA nosocomial pneumonia.


METHODS
This retrospective cohort study involved adults with MRSA nosocomial pneumonia treated with vancomycin. Vancomycin MICs were determined using Etest. Patients with MRSA and vancomycin MICs ≥ 1.5 μg/mL and those with MRSA and MICs ≤ 1 μg/mL were placed in the high- and low-MIC group, respectively. The primary outcomes assessed were clinical response and relapse of MRSA pneumonia within 28 days after vancomycin discontinuation. Secondary outcomes included 28-day mortality, in-hospital mortality and length of hospital stay.


RESULTS
Seventy patients met the inclusion criteria. Mean age and mean Acute Physiological and Chronic Health Evaluation (APACHE) II score upon intensive care unit (ICU) admission of these patients were 67.0 years and 25.9, respectively. Thirty-four (48.6%) isolates had high vancomycin MICs, and 36 (51.4%) had low MICs. There were no significant differences in baseline characteristics between the two groups. Early clinical response rates in the low- and high-MIC groups were 63.9% and 35.3%, respectively (p = 0.031). The high-MIC group had an 8% lower final clinical response rate, but this difference was not significant (p = 0.609). The relapse rate within 28 days was significantly higher in the high-MIC group than in the low-MIC group (29.6% versus 6.9%, p = 0.038). On multivariate analysis, infection by high-MIC strains was an independent predictor of early clinical response failure.


CONCLUSIONS
About half of the MRSA isolates had high vancomycin MIC. Patients infected with these strains showed slower clinical response and higher relapse rate than patients infected with low vancomycin MIC isolates.
Department of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Songpa-gu, Seoul, Korea.
Eun Young
EY
Choi
Jin Won
JW
Huh
Chae-Man
CM
Lim
Younsuck
Y
Koh
Sung-Han
SH
Kim
Sang-Ho
SH
Choi
Yang Soo
YS
Kim
Mi-Na
MN
Kim
Sang-Bum
SB
Hong
D018806:APACHE; D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D015331:Cohort Studies; D003428:Cross Infection / Q000188:drug therapy; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008297:Male; D008485:Medical Audit; D016106:Methicillin Resistance / Q000187:drug effects; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D011023:Pneumonia, Staphylococcal / Q000188:drug therapy; D056910:Republic of Korea; D012189:Retrospective Studies; D013203:Staphylococcal Infections / Q000188:drug therapy*; D013211:Staphylococcus aureus / Q000187:drug effects; D016896:Treatment Outcome; D014640:Vancomycin / Q000494:pharmacology* / Q000627:therapeutic use
D000900:Anti-Bacterial Agents; D014640:Vancomycin
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