How To Choose Appropriate Antibiotics For Diabetic Foot Infections

By Guy Pupp, DPM, FACFAS, and Chad Westphal, DPM

   Diabetes is clearly an epidemic in this country. According to the most recent statistics from the Centers for Disease Control and Prevention, 18.2 million people in the United States have the disease and 1.3 million new cases are diagnosed each year. Foot infection is the most common reason for lower extremity amputation and leads to billions of dollars a year in hospitalization costs in this country alone.

   Despite becoming almost commonplace, diabetic foot infections are often mismanaged, particularly with regard to antibiotics. The solution to this problem requires a strong knowledge of diagnostic essentials, culture techniques, common pathogenic isolates, and appropriate antibiotic selection and usage.1

   Infection typically arises in patients with diabetes secondary to a neuropathic ulceration. Neuropathy causes disturbances in sensory, motor and autonomic function, leading to tissue breakdown from underlying foot pathology or trauma. Once the protective epidermal layer is violated, normal skin flora and environmental microorganisms are free to colonize in the underlying tissues. Depending on the patient’s vascular status, the proliferation and extension of bacteria into deeper tissues can be rapid and life threatening.2-5

   Proper clinical evaluation of the diabetic foot is paramount. Upon the initial presentation of the patient with a diabetic ulceration, one must first examine the wound for local signs of infection including edema, warmth, surrounding erythema, ascending cellulitis, purulence, malodor, sinus tract formation, crepitation, depth of probe and pain. Clinicians should also check for systemic signs of infection including nausea, vomiting, fever, chills, tachycardia and malaise. However, keep in mind that systemic signs of infection rarely accompany diabetic foot infections.6

   Following the initial clinical evaluation, assess the wound and infection severity. The initial visual inspection of the limb, the presence of local and systemic signs, and radiographic evaluation often provide all the information necessary to formulate a treatment regimen. The severity of the infection will dictate whether the patient needs oral or parenteral antibiotics, hospitalization or surgical intervention.

When Should You Culture A Wound?

   One of the greatest controversies in treating diabetic foot infections is when and how to culture a wound appropriately. Culturing a clinically uninfected wound is a mistake that many inexperienced physicians make and doing so can be worse than taking no culture at all. This mistake can lead to the prescribing of an unnecessary, often broad spectrum antibiotic for organisms that are simply contaminants or colonizers. Poor clinical judgment such as this is helping to fuel the rising prevalence of antibiotic resistant organisms such as methicillin resistant Staphylococcus aureus (MRSA) and vancomycin resistant Enterococci (VRE).7

   A culture will identify the underlying pathogens but only if one collects the specimens properly. A common mistake that clinicians make is swabbing the surface of a superficial ulceration without prior wound cleansing or debridement. This results in a mixed flora that significantly lowers the culture’s sensitivity. A deep tissue culture from the base of a cleansed and thoroughly debrided ulceration provides the most accurate results. A bone biopsy can diagnose osteomyelitis if there is clinically exposed bone. Clinicians can send collected specimens to a lab for aerobic, anaerobic, acid fast and fungal culture, and sensitivity evaluation.8

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