A Guide To Current And Emerging Antibiotics For MRSA
Staphylococcus aureus is a common pathogen that can result in everything from minor skin infections to osteomyelitis, bacteremia, endocarditis and pneumonia.1 In podiatry, infections with Staphylococcus aureus, especially methicillinresistant Staphylococcus aureus (MRSA), are something physicians see on a daily basis.
In a study determining the prevalence of MRSA in infected and uninfected diabetic foot ulcers, 61 percent of infected diabetic foot ulcers were infected with MRSA.2 With the emergence of multi-drug resistant Staphylococcus aureus organisms, the need for effective antibiotics has become critical.
Staphylococcus aureus is a highly adaptable gram-positive bacterium that has garnered a lot of attention in the community and the media.There are reports that nearly 50 percent of Staphylococcus aureus isolates are methicillin-resistant.1 While the incidence of hospital-acquired MRSA (HA-MRSA) has increased, there has been a more concerning emergence of communityacquired MRSA (CA-MRSA). This was first reported in the late 1990s when four Native American children died of CA-MRSA related illnesses.
The Staphylococcus aureus involved in these infections have genes that code for Panton-Valentine leukocidin and mecA, the gene that encodes for the organism’s methicillin resistance. In the United States, the most common variant of CA-MRSA is USA300 and accounts for 60 to 75 percent of all Staphylococcus aureus isolates.3
Recognizing The Limitations Of Vancomycin
Vancomycin is generally considered the first line treatment for MRSA infections. Patients take vancomycin in doses of 1g every 12 hours intravenously.
While there is good evidence supporting the use of vancomycin in treating skin and skin structure infections, the outcomes in treating more severe infections such as pneumonia, endocarditis and meningitis are less favorable. For example, researchers found that vancomycin had a clinical success rate of 31.8 percent in a randomized trial for the treatment of MRSA endocarditis and bacteremia.1
While vancomycin has maintained near 100 percent susceptibility in vitro, there is concern regarding increasing minimum inhibitory concentrations (MICs) of Staphylococcus aureus to vancomycin.There have been reports of MRSA isolates with intermediate susceptibility and complete resistance to vancomycin, the so-called vancomycin-intermediate and vancomycin- resistant Staphylococcus aureus (VISA and VRSA).These trends stress the importance of finding new treatment options for MRSA.