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Vancomycin In Vitro Killing Time of MRSA Correlates to Patient Outcomes: Presented at IDSA

By Ed Susman

SAN FRANCISCO, CA -- October 10, 2005 -- The less time it takes vancomycin to kill off strains of methicillin-resistant Staphylococcus aureus (MRSA), the more quickly the antibiotic will work in the infected patients. Researchers presented these findings here October 7^th at the 43^rd Annual Meeting of the Infectious Diseases Society of America (IDSA).

"In patients with MRSA bacteremia, in vitro activity was significantly related to the time to bacterial eradication, probability of microbiologic success, and all-cause mortality," said Pamela Moise-Broder, PharmD, a researcher with CPL Associates LLC, Amherst, New York.

Specifically, the researchers found that if vancomycin in the test tube did not cause at least a 2.5log₁₀ fall in MRSA within 24 hours, patients did not fare as well as those with a more intense in vitro killing rate.

Doctors collected 34 MRSA samples from 34 patients and tested them in the laboratory. The rate of reduction of MRSA was then compared with the patients' outcomes data.

Dr. Moise-Broder said that 30-day mortality was 14% among patients whose samples of MRSA were reduced by 2.5log₁₀ or more within 24 hours. However, in patients in which the rate of eradication was longer than 24 hours, the 30-day mortality was 46%, a difference that, despite the small numbers of patients in the trial, still achieved statistical significance at the P = .041 level.

The average age of the patients in the study was 66 years, and half the patients were treated in the intensive care unit. Of the 23 patients with a > 2.5log₁₀ eradication within 24 hours, the time to discharge was 6 days. For those with the slower killing rate, the time to discharge was 10.5 days, Dr. Moise-Broder said. That difference reached statistical significance at the P = .014 level.


[Presentation title: Relationship Between Time to Eradication In Vivo and Bactericidal Activity In Vitro of Vancomycin for MRSA Infections. Abstract 539]

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