Staphylococcus
infectionCredit: Bill Branson
New research suggests the antibiotic vancomycin is still effective in treating Staphylococcus aureus bloodstream (SAB) infections, despite increases in minimum inhibitory concentration (MIC) values.
Researchers found no difference in mortality between patients with low-vancomycin MIC and those with high-vancomycin MIC.
So it seems physicians can continue using vancomycin when MIC values are elevated but within the susceptible range, rather than
switching to newer antibiotics.
Andre Kalil, MD, of the University of Nebraska Medical Center in Omaha, and his colleagues described this research in JAMA.
In recent years, physicians treating Staphylococcus infections with vancomycin have seen an increase in the MIC, the lowest concentration of an antimicrobial agent that inhibits the growth of a microorganism.
MIC values lower than 4 mg/L suggest Staphylococcus is susceptible to vancomycin. However, when the MIC value exceeds 1.5 mg/L, some physicians have taken it as an indication that vancomycin may not be working at maximum effectiveness.
Some reports have suggested that elevations in vancomycin MIC values may be associated with increased treatment failure and death.
To determine the effectiveness of vancomycin, Dr Kalil and his colleagues analyzed data from 38 studies covering 8291 episodes of SAB infection.
The team evaluated the association between vancomycin MIC elevation and mortality. Among all SAB infections studied, the overall mortality was 26.1%.
The adjusted absolute risk of mortality did not differ significantly between patients with high-vancomycin MIC and those with low-vancomycin MIC—26.8% and 25.8%, respectively.
In studies that included only methicillin-resistant Staphylococcus aureus infections, the mortality among SAB episodes in patients with high-vancomycin MIC was 27.6%, compared with a mortality of 27.4% among patients with low-vancomycin MIC.
“The study provides strong evidence that vancomycin remains highly useful,” Dr Kalil said. “Even though vancomycin is an older drug, it is still killing staph very efficiently. There are newer antibiotics available to treat Staphylococcus aureus infections, but this study demonstrates that physicians don’t necessarily need to switch to these new drugs when the MIC is increased but still within the susceptible range.”
“The prevention of a rapid switch to newer drugs has another great benefit to our patients—less unnecessary exposure to these drugs, which will translate into less development of antibiotic resistance.”
Dr Kalil said the study may have implications for clinical practice and public health.
The results suggest standards for vancomycin MIC likely do not need to be lowered, routine differentiation of MIC values between 1 mg/L and 2 mg/L appears unnecessary, and the use of alternative drugs may not be required for Staphylococcus aureus isolates with elevated but susceptible vancomycin MIC values.
