Assessing and treating infected diabetic foot wounds can be challenging. Providing timely treatment is essential given the potential complications of diabetic foot infections but the rise in antibiotic resistance is a key issue to consider. With this in mind, our expert panelists discuss a variety of issues, ranging from empiric antibiotic selection and MRSA infected wounds to their approach in diagnosing osteomyelitis.
Q: What empiric antibiotics do you utilize for the infected neuropathic diabetic foot ulcer?
A: Systemic antibiotics are unnecessary unless there is evidence of osteomyelitis or active cellulitis, explains Anthony F. Cutrona, MD. All of the panelists agree that whenever possible, the antibiotic regimen should be tailored to the results of deep tissue cultures. However, as Leon Brill, DPM, points out, there are times when you need to start empiric therapy as soon as possible. He also cautions that cultures are unreliable when patients have already been on a prolonged course of multiple antibiotics.
When it comes to empiric antibiotics, Dr. Brill says he always tries to provide coverage for Staph and Strep, preferring to use ampicillin/sulbactam for hospital patients and amoxicillin/clavulanate for outpatients. For skin and soft tissue infection, Dr. Cutrona utilizes oral empiric antibiotics such as doxycycline, trimethoprimsulfa, clindamycin, quinolones, metronidazole and linezolid. While all of these antibiotics have “excellent bioavailability,” Dr. Cutrona says one should weigh the cost issue. He notes that while doxycycline and metronidazole may be as cheap as 20 cents a tablet, a tablet of linezolid is $100.
When providing empiric treatment for patients who are not allergic to penicillin, Lawrence G. Karlock, DPM, says he opts for amoxicillin/clavulanate 875 mg bid or cefdinir 300 mg bid. For those who are allergic to penicillin, Dr. Karlock will usually combine an empiric combination of levaquin 750 mg qd with clindamycin 300 mg qid. When treating penicillin-allergic patients, Dr. Brill uses clindamycin empirically. He notes he may also add levofloxacin to extend the spectrum for both in-patients and outpatients.
Deeper infectious processes require intravenous antibiotics, according to Dr. Cutrona. When it comes to empiric IV antibiotics, Dr. Cutrona says combining beta-lactams (piperacillin-tazobactam, the fourth generation cephalosporin carbopenem) with clindamycin is “very effective.” He points out that clindamycin is synergistic with beta-lactam in Strep infections. If one is concerned about methicillin-resistant Staph aureus (MRSA), Dr. Cutrona says vancomycin can be an additive.
Q: What factors influence your decision to treat these patients on an outpatient basis versus admission to the hospital?
A: Dr. Cutrona says one should evaluate the patient’s vitals. If the patient has hypotension, fever or exhibits lethargy or confusion, Dr. Cutrona says any of these signs would be a “basis for admission with or without significant local problems.” Dr. Brill concurs, noting that he admits patients who display constitutional symptoms of fever or malaise.
However, Dr. Karlock points out that a large percentage of diabetic patients with foot threatening infections do not necessarily develop these constitutional symptoms and may not necessarily show a left shift or a leukocytosis. Given this, Dr. Karlock says “We do not always base our decision to hospitalize these patients on this criteria.”
When determining the severity of the infection, Dr. Brill notes that he does not rely heavily on white blood cell counts or temperature because “these may remain low even in the face of sepsis due to the immunocompromised nature of the patient.”
All patients who require deep surgical debridement are admitted for IV antibiotics, wound care and offloading, according to Dr. Brill. Dr. Karlock says he will admit patients whom he suspects of having osteomyelitis. He adds that whether the patient needs an I&D is another factor influencing a possible admission. When assessing the foot wound, one should take into account the odor, cellulitis, the possibility of expressing purulence, findings of gangrene of the skin and soft tissue, and the depth of the wound and whether you can probe to bone. Dr. Cutrona says all of these factors would influence admission to the hospital. Dr. Brill concurs, noting that rapidly progressing cellulitis would warrant hospital admission.
One should also consider the possibility of a vascular problem as a comorbid concern, notes Dr. Cutrona. Dr. Karlock says the general health status of the patient also comes into play. For example, he would want to admit patients who are on renal dialysis for more aggressive treatment.
The patient’s social structure (specifically the availability of a caregiver) plays a role in making the decision to treat patients as outpatients or admitting them to the hospital.
“If the patient has a good support system at home to treat this wound, we’ll try to treat on an outpatient basis,” explains Dr. Karlock. “However, if the patient has a poor social structure at home, admission into the hospital is usually more appropriate.”
Q: How do you approach the MRSA infected wound?
A: Dr. Brill says MRSA and vancomycin resistant Staph aureus (VRSA) are becoming “alarmingly increasing” problems in the community he serves. More specifically, Dr. Karlock says MRSA accounts for upward of 40 percent of all Staph aureus isolates at one of the local hospitals in his area. Dr. Cutrona says 65 percent of the Staph aureus cases at his facility are MRSA.
Dr. Brill says one should have a strong index of suspicion for MRSA when assessing patients who have diabetic wounds of long duration and a long history of single or multiple oral and/or topical antibiotic use. For these patients, Dr. Brill will pursue empiric treatment with vancomycin in the hospital and trimethoprim/sulphamethoxazole for outpatients. If the patients are allergic to sulphamethoxazole, Dr. Brill says he will substitute a tetracycline instead. Due to increasing resistance, Dr. Brill says he reserves daptomycin and linezolid for resistant cases. In these cases, he always obtains an infectious disease consult.
MRSA strains are more prevalent in the hospital, according to Dr. Cutrona. He says these strains are resistant to most oral antibiotics and are sensitive to vancomycin, linezolid and rifampin. Dr. Cutrona says outpatient MRSA tends to be sensitive to the aforementioned antibiotics as well as doxycycline, clindamycin and trimethoprimsulfa.
He emphasizes that treating MRSA is no different than treating penicillin- or methicillin-sensitive Staph aureus. If the wound involves deep structures, such as tendon, ligament or bone, Dr. Cutrona says IV antibiotics are necessary as well as aggressive surgical debridement. He emphasizes that clean surgical margins are key to facilitating the effectiveness of the antibiotics. The length of antibiotic therapy depends upon the depth of the wound infection, notes Dr. Cutrona. When there is extension to the bone, he says one will need to proceed with six to eight weeks of IV antibiotics.
Q: In the workup of possible pedal osteomyelitis, what imaging modalities do you prefer to use and why?
A: Drs. Brill and Karlock prefer magnetic resonance imaging (MRI) when they suspect osteomyelitis. Unless plain radiographs unequivocally demonstrate osteomyelitis, Dr. Brill says he prefers MRI because it is noninvasive and “has a fairly reliable sensitivity and specificity.” However, he warns there is a 10 to 20 percent false positive finding with MRIs, which he says is most likely due to neuropathic changes in bone.
For the majority of pedal osteomyelitis, Dr. Karlock says he “usually relies” on standard radiographs as well as probe to bone tests. Dr. Cutrona agrees, noting that changes in serial plain X-rays should enable one to make the diagnosis. Dr. Karlock says he occasionally uses the Tc99 bone scan to rule out osteomyelitis. If he is dealing with a deep wound and wants to determine whether it is a soft tissue infection or osteomyelitis, Dr. Karlock says he will order the Tc99 to confirm there is no bony infection in the foot. He emphasizes this is not commonplace in his practice.
Bone scans and the white blood cell tag in the scans seem to be unreliable in assessing patients with diabetes, according to Dr. Cutrona, who cites false positive and negatives in the range of 60 percent. He says these tests are “very expensive,” and for about the the same cost, one can obtain good anatomical resolution either by CT scan or MRI. Dr. Karlock agrees, noting that he usually does not order multiple tests and/or scans in this clinical setting.
“I have found that ordering all these tests can actually become more confusing and lead you down the wrong path,” cautions Dr. Karlock.
In summary, Dr. Cutrona emphasizes the importance of diagnosing osteomyelitis on both a clinical basis as well as through laboratory data, radiographic data and, if possible, a biopsy.
Dr. Brill practices at the Limb Salvage Center at the BrillStone Building and is President of the BrillStone Corporation in Dallas. He is a Fellow of the American College of Foot and Ankle Surgeons and is also a consultant in wound care and reconstructive foot and ankle surgery at the Wound Care Clinic at Presbyterian Hospital in Dallas.
Dr. Cutrona is the Director of the Infectious Disease Section of the St. Elizabeth Health Center in Youngstown, Ohio.
Dr. Karlock (pictured) is a Fellow of the American College of Foot and Ankle Surgeons and practices in Austintown, Ohio. He is a member of the Editorial Advisory Board for WOUNDS, a Compendium of Clinical Research and Practice.