Keys To Addressing MRSA In The Diabetic Foot

Suhad Hadi, DPM, FACFAS, and Randy Garr, DPM

What The IDSA Recommends For Diabetic Foot Infections

By following the guidelines established by the IDSA in identifying and categorizing diabetic foot infections, one has a strong foundation for approaching empiric therapy and antibiotic selection. The guidelines define infections as uninfected, mild, moderate and severe.4 The guideline authors further define each category with distinct clinical manifestations and appropriate management options (see “A Guide To The IDSA Diabetic Foot Infection Classification” below at left).

   Uninfected wounds. There are no signs of infection. There is a healthy wound or ulcer in the absence of erythema, warmth, purulence/discharge, swelling or pain. Monitor these patients with aggressive wound hygiene, appropriate offloading and follow-up care.

   The progression to infected wounds is defined by the presence of at least two of the following items: local swelling or induration; erythema; local tenderness or pain; local warmth and purulent discharge (thick, opaque to white sanguineous drainage).

   Mild infections. These ulcers or wounds demonstrate clinical signs of infection that only affect the skin and subcutaneous tissue. There is an absence of deep tissue involvement and systemic signs of infection. The presence of peri-ulcer erythema is confined to a width of 0.5 to 2.0 cm. It is important in these types of wounds and suspected infections to rule out other sources of skin inflammation.

   Moderate infections. These infections involve wider parameters in regard to depth of tissue involvement and surrounding erythema. These infections are associated with deep tissue involvement beyond the subcutaneous tissue. They are often at risk for osteomyelitis and deep abscess formation. However, systemic inflammatory response syndrome signs are not present in patients with moderate infections.

   Severe infections. These infections incorporate the above findings with the presence of two or more manifestations of systemic inflammatory response signs. These manifestations include:

• a body temperature less than 36°C (96.8°F) or greater than 38°C (100.4°F);
• a heart rate greater than 90 beats per minute;
• tachypnea >20 breaths per minute or an arterial CO2 partial pressure less than 4.3 kPa (32 mmHg);
• a white blood cell count 12,000 cells/mm³ (12 x 109 cells/L); or the presence of greater than 10 percent immature neutrophils (band forms).4

How To Choose Among Antibiotic Treatment Options

When it comes to patients with confirmed MRSA or at-risk hospitalized patients who have a previous history of MRSA infections, it is important to ensure appropriate bacterial coverage with the initial antibiotic regimen. In the absence of risk factors and during a period of pending cultures, it is best to initiate broad spectrum coverage and include MRSA coverage in the initial antibiotic regimen. Upon confirmation of final cultures, one may tailor the antibiotic regimen to a more focused selection or, when necessary, combination therapy.

   The IDSA also provides recommendations and therapeutic guidelines for antibiotic selection. In patients with first time infections and no prior antibiotic treatment, it is appropriate to cover for methicillin susceptible S. aureus (MSSA) as opposed to MRSA. The consensus is to avoid using antibiotics in uninfected wounds in an attempt to reduce the risk of colonization and infection with resistant bacteria. Always initiate anti-MRSA therapy in high-risk patients with a history of MRSA, chronic wounds or ulcers, severely immunocompromised states, etc.

   Where vancomycin was at one time the mainstay for management of MRSA, there has been increasing concern for resistance to the drug. This is a precise reminder of the rapid virulence of S. aureus. Despite a decline in the development of newer antibiotics, there are currently a number of antibiotic options for the treatment of MRSA and a variety of oral options. It is critical to remember, however, that these antibiotics come with risks. Close monitoring of renal and/or hepatic function is often crucial and one must appropriately adjust the dosing.

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