Vancomycin no longer 'old dependable' against MRSA, roundtable warns

August 11, 2008

The evolution of MRSA has led to reduced efficacy of vancomycin therapy.

The evolution of methicillin-resistant Staphylococus aureus (MRSA) has led to the reduced efficacy of vancomycin therapy.

"In my experience, vancomycin is no longer a reliable therapeutic choice for patients with serious S. aureus infections," Stan Deresinski, M.D., clinical professor of medicine, Stanford University, said in New York at a Cubist Pharmaceuticals-sponsored roundtable of infectious disease experts.

MRSA, the so-called " superbug" because of its drug-resistance, was originally seen only in hospitalized patients with compromised immune systems. Later it became prevalent in the community. Today new and different strains of MRSA, genetically distinct from early varieties and often more virulent, are again appearing beyond the hospital.

New York has received 676 MRSA reports since February, Tice said. "But these cases probably represent only the tip of the iceberg since just 21 labs out of 49 have been reporting." Around 4,000 cases are likely more accurate, he added.

Michael Rybak, Pharm.D., MPH, Wayne State University, said, "Compared to the multidrug resistance often seen in hospital-acquired MRSA strains, most community-associated (CA)-MRSA isolates remain susceptible to tetracyclines, clindamycin, and trimethoprim-sulfamethoxazole (TMP-SMZ )."

Deresinski added the following to his list of antibiotics to which varieties of MRSA remain vulnerable:

Quinupristin/dalfopristin: "This combination is bactericidal against S. aureus but only bacteriostatic against other pathogens," he said. In one randomized trial comparing the daily combination with vancomycin, patients with hospital-acquired MRSA pneumonia who had received the daily combination had a clinical response rate of 19.4% compared with 40% in vancomycin recipients.

Linezolid: In a randomized open-label trial comparing linezolid and vancomycin, the two agents yielded similar results in hospitalized patients with MRSA infections. Additionally, another comparator trial suggested that linezolid is superior to vancomycin as a treatment for hospital-acquired pneumonia due to MRSA.

Daptomycin: Deresinski described the recently approved agent as a "novel lipopeptide antibiotic with bactericidal activity against S. aureus that binds to the bacterial cell membrane, disrupting membrane potential." At the same time, daptomycin is ineffective in treating pneumonia, he said.

Fluoroquinolones: While most CA-MRSA strains are susceptible to fluoroquinolones, this is not true for all MRSA strains, Deresinksi said.

THE AUTHOR is a writer based in New York.