From the Guidelines
Diabetic foot infections are most commonly caused by aerobic gram-positive cocci, particularly staphylococci, and are often polymicrobial, including aerobic gram-negative bacilli and obligate anaerobes. The most recent and highest quality study, 1, suggests that the classification of diabetic foot infections into mild, moderate, or severe, along with a vascular assessment, helps determine the appropriate treatment approach.
Key Organisms
- Aerobic gram-positive cocci (GPC), especially staphylococci, are the most common causative organisms
- Aerobic gram-negative bacilli are frequently copathogens in chronic or previously treated infections
- Obligate anaerobes may be copathogens in ischemic or necrotic wounds
Treatment Approach
- Empiric antibiotic therapy can be narrowly targeted at GPC in many acutely infected patients
- Patients at risk for infection with antibiotic-resistant organisms or with chronic, previously treated, or severe infections usually require broader spectrum regimens
- Cultures from deep tissue samples, rather than superficial swabs, should guide definitive therapy
- Imaging, such as plain radiographs or magnetic resonance imaging, is helpful in most diabetic foot infections to diagnose and manage complications like osteomyelitis.
Management
- Most diabetic foot infections require some surgical intervention, ranging from minor (debridement) to major (resection, amputation)
- Wounds must be properly dressed and off-loaded of pressure, and patients need regular follow-up
- Employing multidisciplinary foot teams improves outcomes, and clinicians and healthcare organizations should attempt to monitor and improve their outcomes and processes in caring for diabetic foot infections, as suggested by 1.
From the FDA Drug Label
The cure rates by pathogen for microbiologically evaluable patients are presented in Table 19. Table 19 Cure Rates at the Test-of-Cure Visit for Microbiologically Evaluable Adult Patients with Diabetic Foot Infections Pathogen Cured ZYVOXn/N (%) Comparatorn/N (%) Staphylococcus aureus 49/63 (78) 20/29 (69) Methicillin-resistant S aureus 12/17 (71) 2/3 (67) Streptococcus agalactiae 25/29 (86) 9/16 (56)
The most common organisms causing diabetic foot infections are Staphylococcus aureus, Methicillin-resistant S aureus, and Streptococcus agalactiae.
- Staphylococcus aureus was cured in 78% of patients treated with linezolid and 69% of patients treated with the comparator.
- Methicillin-resistant S aureus was cured in 71% of patients treated with linezolid and 67% of patients treated with the comparator.
- Streptococcus agalactiae was cured in 86% of patients treated with linezolid and 56% of patients treated with the comparator 2.
From the Research
Diabetic Foot Infection Organisms
- The most common pathogens involved in diabetic foot infections are aerobic Gram-positive cocci, particularly Staphylococcus aureus (including methicillin-resistant S. aureus (MRSA)) 3, 4, 5, 6.
- Gram-negative bacteria and anaerobes may also be present, especially in chronic or previously treated wounds 3, 5, 6.
- Staphylococcus aureus small colony variants (SCVs) can also cause diabetic foot infections and are often resistant to antimicrobial therapy 7.
- The global ratio of methicillin-sensitive S aureus to methicillin-resistant S aureus (MRSA) was found to be 1.3:1 in one study 4.
Antibiotic Therapy Considerations
- Initial antibiotic therapy for diabetic foot infections is usually empirical and should cover aerobic Gram-positive cocci, including Staphylococcus aureus 3, 5, 6.
- Broad-spectrum therapy may be necessary for severe infections, while less severe infections may be treated with narrower-spectrum agents 3, 5, 6.
- Anti-anaerobe agents should be considered for necrotic or gangrenous infections on an ischemic limb 3.
- Piperacillin/tazobactam may be a suitable option for empiric antibiotic therapy in diabetic foot infections 4.