Antimicrobial interventions for the management of diabetic foot infections

The role of anaerobes in diabetic foot infections

Diabetic foot infections (DFI) are a common cause of morbidity and, on occasion, even mortality. Infection can be either mono- or polymicrobial, with a wide variety of potential pathogens. Anaerobes may be involved, particularly in wounds that are deeper or more chronic, and are more frequently identified when using modern molecular techniques, such as 16s PCR and pyrosequencing. It remains unclear whether the presence of anaerobes in DFI leads to more severe manifestations, or if these organisms are largely colonizers associated with the presence of greater degrees of tissue ischemia and necrosis. Commonly used empiric antibiotic therapy for diabetic foot infections is generally broad-spectrum and usually has activity against the most frequently identified anaerobes, such as Peptostreptococcus and Bacteroides species. Adequate surgical debridement and, when needed, foot revascularization may be at least as important as the choice of antibiotic to achieve a successful treatment outcome.

Diabetic foot infections: state-of-the-art

Foot infections are frequent and potentially devastating complications of diabetes. Unchecked, infection can progress contiguously to involve the deeper soft tissues and ultimately the bone. Foot ulcers in people with diabetes are most often the consequence of one or more of the following: peripheral sensory neuropathy, motor neuropathy and gait disorders, peripheral arterial insufficiency or immunological impairments. Infection develops in over half of foot ulcers and is the factor that most often leads to lower extremity amputation. These amputations are associated with substantial morbidity, reduced quality of life and major financial costs. Most infections can be successfully treated with optimal wound care, antibiotic therapy and surgical procedures. Employing evidence-based guidelines, multidisciplinary teams and institution-specific clinical pathways provides the best approach to guide clinicians through this multifaceted problem. All clinicians regularly seeing people with diabetes should have an understanding of how to prevent, diagnose and treat foot infections, which requires familiarity with the pathophysiology of the problem and the literature supporting currently recommended care.

Diagnosis and management of infection in the diabetic foot

Foot infections are common in persons with diabetes mellitus. Most diabetic foot infections occur in a foot ulcer, which serves as a point of entry for pathogens. Unchecked, infection can spread contiguously to involve underlying tissues, including bone. A diabetic foot infection is often the pivotal event leading to lower extremity amputation, which account for about 60% of all amputations in developed countries. Given the crucial role infections play in the cascade toward amputation, all clinicians who see diabetic patients should have at least a basic understanding of how to diagnose and treat this problem.

Novel antibiotics for the management of diabetic foot infections

Foot infections are a major cause of morbidity in diabetic patients. Staphylococcus aureus is the most important pathogen in mild infections; moderate to severe infections are frequently polymicrobial. Multidrug resistance is an increasing problem in isolates from diabetic feet. Worldwide, up to 30% of patients with diabetic foot infection (DFI) are colonised with methicillin-resistant S. aureus (MRSA), whilst extended-spectrum beta-lactamase-producing Gram-negative bacteria are also common in some countries. This emergence of drug resistance has coincided with the launch or imminent availability of many new antibiotics. Most of these were developed to target multidrug-resistant Gram-positive bacteria, although some have a spectrum of activity that includes Gram-negative bacteria and anaerobes. There is a variable amount of experience with these agents in treating skin and skin-structure infections (SSSIs), especially for DFI. However, at least some have a spectrum of activity and/or pharmacological properties that suggest that they may be of value in managing DFIs. The aim of this paper is to review evidence for the efficacy of new antibiotics in the management of SSSIs, including any data relating specifically to the diabetic foot, and to consider where they might fit into the therapeutic armory against DFI.

Efficacy and safety of neutral pH superoxidised solution in severe diabetic foot infections

The use of antiseptics in wound care is often controversial and there is definitely a need for a non toxic, highly disinfective agent. This study assessed the efficacy of a neutral pH superoxidised aqueous solution (NpHSS) for infection control, odour reduction and surrounding skin and tissue damage on infected diabetic foot ulcerations. From November 2003 to March 2004, 45 patients with type 2 diabetes were randomised into a single-blind clinical trial comparing NpHSS (intervention group; n = 21) versus conventional disinfectant (control group; n = 16). All patients received comprehensive care including surgical debridement as appropriate, moist wound care, intensive glucose control and broad spectrum antibiotics. Treatment groups were matched in terms of sex, age (61.9 +/- 11.9 versus 67.8 +/- 11.6), years of diabetes duration (16.4 +/- 8.1 versus 17 +/- 10.2), obesity, HgAlc (7.1 +/- 2 versus 6.7 +/- 1.8), initial fasting glycaemia (163 +/- 59 versus 152 +/- 65.8 mg/dl), ulcer duration/week (13.7 +/- 24 versus 15.1 +/- 16.3), B/A Index (0.9 +/- 0.5 versus 1.14 +/- 0.7), depth and extent of infection/periwound cellulitis (groups B and C of the Tampico Hospital Classification) as well as aetiology (P = 0.647). Odour reduction was achieved in all NpHSS patients (100% versus 25%; P < 0.01) and surrounding cellulitis diminished (P < 0.001) in 17 patients (80.9% versus 43.7%). Nineteen patients in the NpHSS group showed advancement to granulating tissue stage (90.4% versus 62.5%; P = 0.05) with significantly less tissue toxicity (94% versus 31.2%; P < 0.01). A non toxic, NpHSS, as part of a comprehensive care regimen, may be more efficacious in infection control, odour and erythema reduction than conventional disinfectants in treatment of diabetic foot infections.

Clinical management of diabetic foot infection: diagnostics, therapeutics and the future

Diabetic foot infection accounts for a substantial global burden of morbidity, psychosocial disruption and economic cost. Recommendations for best practice are continuously evolving in parallel with improvements in imaging modalities, development and clinical use of new antimicrobial agents and data surrounding novel adjunctive strategies. We discuss this complex group of infections with a particular emphasis on medical management of osteomyelitis, while also highlighting the importance of a broad multidisciplinary approach to eradicating infection.

Optimising Antimicrobial Therapy in Diabetic Foot Infections

Foot infections are common and the most serious lower extremity complication contributing to amputations, particularly in patients with diabetes mellitus. Infection is most often a consequence of foot ulcerations, which typically follows trauma to a neuropathic foot. Foot infections may be classified as mild, moderate and severe; this largely determines the approach to therapy. Gram-positive bacteria are the sole causative pathogens for most mild and moderate infections. These infections can usually be treated with culture-based narrow-spectrum antibacterials along with appropriate surgical debridement in an outpatient setting. In contrast, severe infections are often polymicrobial, requiring hospitalisation and treatment with broad-spectrum antibacterials along with appropriate medical and surgical interventions. The initial empirical antibacterial regimen may be tailored based on the results of culture and sensitivity tests from properly obtained specimens. Several antibacterial regimens have demonstrated effectiveness in randomised controlled trials, but no single regimen has shown superiority. Managing diabetic foot osteomyelitis is particularly controversial and requires reliable cultures to select an appropriate antibacterial regimen. Surgical resection of the infected and necrotic bone favours a good outcome in chronic osteomyelitis. The recommended duration of antibacterial therapy ranges from 1 to 4 weeks for soft tissue infection, to >6 weeks for unresected osteomyelitis. The incidence of meticillin-resistant Staphylococcus aureus infection is increasing in both the healthcare setting and the community. This should be considered when selecting an antibacterial, especially if the patient does not improve with initial antibacterial therapy. Certain other organisms, such as Pseudomonas aeruginosa and Enterococcus spp., while potentially pathogenic, are often colonisers that do not require targeted therapy.

Ertapenem versus piperacillin/tazobactam for diabetic foot infections (SIDESTEP): prospective, randomised, controlled, double-blinded, multicentre trial

BACKGROUND

Diabetic foot infections are a common and serious problem, yet few randomised trials of adequate quality have compared the efficacy of the various antibiotic regimens available for their treatment. Our aim was to assess the efficacy and safety of ertapenem versus piperacillin/tazobactam for foot infections.

METHODS

We did a randomised, double-blinded, multicentre trial in adults (n=586) with diabetes and a foot infection classified as moderate-to-severe and requiring intravenous antibiotics. We assigned patients intravenous ertapenem (1 g daily; n=295) or piperacillin/tazobactam (3.375 g every 6 h; n=291) given for a minimum of 5 days, after which oral amoxicillin/clavulanic acid (875/125 mg every 12 h) could be given for up to 23 days. Investigators retained the option to administer vancomycin to patients in either group to ensure adequate coverage for potentially antibiotic resistant Enterococcus spp and meticillin-resistant Staphylococcus aureus (MRSA). Our primary outcome was the proportion of patients with a favourable clinical response (cure or improvement) on the day that intravenous antibiotic was discontinued. Analyses were by an evaluable-patient only approach. This study is registered with , number NCT00229112.

FINDINGS

Of the 576 patients treated, 445 were available for assessment at the end of intravenous therapy. Both baseline characteristics and favourable clinical response rates were similar for the 226 who received ertapenem and the 219 who received piperacillin/tazobactam (94%vs 92%, respectively; between treatment difference 1.9%, 95% CI -2.9 to 6.9). Rates of favourable microbiological responses (eradication rates and clinical outcomes, by pathogen) and adverse events did not differ between groups.

INTERPRETATION

Clinical and microbiological outcomes for patients treated with ertapenem were equivalent to those for patients treated with piperacillin/tazobactam, suggesting that this once-daily antibiotic should be considered for parenteral therapy of diabetic foot infections, when deemed appropriate.