Linezolid - Resistance

Resistance

Acquired resistance to linezolid was reported as early as 1999, in two patients with severe, multidrug-resistant Enterococcus faecium infection who received the drug through a compassionate use program. Linezolid-resistant Staphylococcus aureus was first isolated in 2001.

In the United States, resistance to linezolid has been monitored and tracked since 2004 through a program named LEADER, which (as of 2007) was conducted in 60 medical institutions throughout the country. Resistance has remained stable and extremely low—less than one-half of one percent of isolates overall, and less than one-tenth of one percent of S. aureus samples. A similar, worldwide program—the "Zyvox Annual Appraisal of Potency and Spectrum Study", or ZAAPS—has been conducted since 2002. As of 2007, overall resistance to linezolid in 23 countries was less than 0.2%, and nonexistent among streptococci. Resistance was only found in Brazil, China, Ireland, and Italy, among coagulase-negative staphylococci (0.28% of samples resistant), enterococci (0.11%), and S. aureus (0.03%). In the United Kingdom and Ireland, no resistance was found in staphylococci collected from bacteremia cases between 2001 and 2006, although resistance in enterococci has been reported. Some authors have predicted that resistance in E. faecium will increase if linezolid use continues at current levels or increases.