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

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.

Ertapenem: the new carbapenem 5 years after first FDA licensing for clinical practice

Ertapenem, a parenteral broad-spectrum 1-beta-methyl-carbapenem, was licensed 5 years ago for clinical practice in the US and Europe. The substance has a good in vitro activity against many common aerobic and anaerobic Gram-positive and -negative bacteria. Its in vitro activity against Enterobacteriaceae carrying plasmid- or chromosomal-mediated beta-lactamases, including AmpC- and extended-spectrum beta-lactamases, is especially clinically significant. Advantages concerning in vitro activity and low potential for so-called 'collateral damage', and development of own resistance during therapy, as shown in several randomized, controlled clinical trials, make ertapenem an excellent treatment choice for complicated aerobic and anaerobic mix infections caused by ertapenem-sensitive bacteria. On the other hand, due to its limited activity against Acinetobacter spp., enterococci and Pseudomonas aeruginosa, it is less suitable for late-onset nosocomial infections. International guidelines recommend the initial empirical use of ertapenem for intra-abdominal infections, skin and skin-structure infections, acute pelvic infections, complicated urinary tract infections and pneumonia (both community-acquired and 'early-onset' nosocomial) in a dose of 1.0 g administered once daily. However, recent results from pharmacokinetic/pharmacodynamic modelling studies in critically ill patients with ventilator-associated pneumonia and adipose volunteers with a body mass index of > or = 20 kg/m(2) showed that the standard dose of 1.0 g/day may not provide adequate free, protein-unbound drug concentrations in plasma and organ tissues. Therefore, a shortening of the dosage interval or continuous infusion of ertapenem should be considered to ensure optimal free concentrations in these particular populations.

Comparative Review of the Carbapenems

The carbapenems are beta-lactam antimicrobial agents with an exceptionally broad spectrum of activity. Older carbapenems, such as imipenem, were often susceptible to degradation by the enzyme dehydropeptidase-1 (DHP-1) located in renal tubules and required co-administration with a DHP-1 inhibitor such as cilastatin. Later additions to the class such as meropenem, ertapenem and doripenem demonstrated increased stability to DHP-1 and are administered without a DHP-1 inhibitor. Like all beta-lactam antimicrobial agents, carbapenems act by inhibiting bacterial cell wall synthesis by binding to and inactivating penicillin-binding proteins (PBPs). Carbapenems are stable to most beta-lactamases including AmpC beta-lactamases and extended-spectrum beta-lactamases. Resistance to carbapenems develops when bacteria acquire or develop structural changes within their PBPs, when they acquire metallo-beta-lactamases that are capable of rapidly degrading carbapenems, or when changes in membrane permeability arise as a result of loss of specific outer membrane porins. Carbapenems (imipenem, meropenem, doripenem) possess broad-spectrum in vitro activity, which includes activity against many Gram-positive, Gram-negative and anaerobic bacteria; carbapenems lack activity against Enterococcus faecium, methicillin-resistant Staphylococcus aureus and Stenotrophomonas maltophilia. Compared with imipenem, meropenem and doripenem, the spectrum of activity of ertapenem is more limited primarily because it lacks activity against Pseudomonas aeruginosa and Enterococcus spp. Imipenem, meropenem and doripenem have in vivo half lives of approximately 1 hour, while ertapenem has a half-life of approximately 4 hours making it suitable for once-daily administration. As with other beta-lactam antimicrobial agents, the most important pharmacodynamic parameter predicting in vivo efficacy is the time that the plasma drug concentration is maintained above the minimum inhibitory concentration (T>MIC). Imipenem/cilastatin and meropenem have been studied in comparative clinical trials establishing their efficacy in the treatment of a variety of infections including complicated intra-abdominal infections, skin and skin structure infections, community-acquired pneumonia, nosocomial pneumonia, complicated urinary tract infections, meningitis (meropenem only) and febrile neutropenia. The current role for imipenem/cilastatin and meropenem in therapy remains for use in moderate to severe nosocomial and polymicrobial infections. The unique antimicrobial spectrum and pharmacokinetic properties of ertapenem make it more suited to treatment of community-acquired infections and outpatient intravenous antimicrobial therapy than for the treatment of nosocomial infections. Doripenem is a promising new carbapenem with similar properties to those of meropenem, although it appears to have more potent in vitro activity against P. aeruginosa than meropenem. Clinical trials are required to establish the efficacy and safety of doripenem in moderate to severe infections, including nosocomial infections.

High prevalence of ischaemia, infection and serious comorbidity in patients with diabetic foot disease in Europe. Baseline results from the Eurodiale study

AIMS/HYPOTHESIS

Large clinical studies describing the typical clinical presentation of diabetic foot ulcers are limited and most studies were performed in single centres with the possibility of selection of specific subgroups. The aim of this study was to investigate the characteristics of diabetic patients with a foot ulcer in 14 European hospitals in ten countries.

METHODS

The study population included 1,229 consecutive patients presenting with a new foot ulcer between 1 September 2003 and 1 October 2004. Standardised data on patient characteristics, as well as foot and ulcer characteristics, were obtained. Foot disease was categorised into four stages according to the presence or absence of peripheral arterial disease (PAD) and infection: A: PAD -, infection -; B: PAD -, infection +; C: PAD +, infection -; D: PAD +, infection +.

RESULTS

PAD was diagnosed in 49% of the subjects, infection in 58%. The majority of ulcers (52%) were located on the non-plantar surface of the foot. With regard to severity, 24% had stage A, 27% had stage B, 18% had stage C and 31% had stage D foot disease. Patients in the latter group had a distinct profile: they were older, had more non-plantar ulcers, greater tissue loss and more serious comorbidity.

CONCLUSIONS/INTERPRETATION

According to our results in this European cohort, the severity of diabetic foot ulcers at presentation is greater than previously reported, as one-third had both PAD and infection. Non-plantar foot ulcers were more common than plantar ulcers, especially in patients with severe disease, and serious comorbidity increased significantly with increasing severity of foot disease. Further research is needed to obtain insight into the clinical outcome of these patients.

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.

The neuropathic diabetic foot

Diabetic foot problems are common throughout the world, and result in major medical, social and economic consequences for the patients, their families, and society. Foot ulcers are likely to be of neuropathic origin and, therefore, are eminently preventable. Individuals with the greatest risk of ulceration can easily be identified by careful clinical examination of their feet: education and frequent follow-up is indicated for these patients. When infection complicates a foot ulcer, the combination can be limb-threatening, or life-threatening. Infection is defined clinically, but wound cultures assist in identification of causative pathogens. Tissue specimens are strongly preferred to wound swabs for wound cultures. Antimicrobial therapy should be guided by culture results, and although such therapy may cure the infection, it does not heal the wound. Alleviation of the mechanical load on ulcers (offloading) should always be a part of treatment. Plantar neuropathic ulcers typically heal in 6 weeks with nonremovable casts, because pressure at the ulcer site is mitigated and compliance is enforced. The success of other approaches to offloading similarly depends on the patient's adherence to the strategy used for pressure relief.

Diabetic foot disorders. A clinical practice guideline (2006 revision)

The prevalence of diabetes mellitus is growing at epidemic proportions in the United States and worldwide. Most alarming is the steady increase in type 2 diabetes, especially among young and obese people. An estimated 7% of the US population has diabetes, and because of the increased longevity of this population, diabetes-associated complications are expected to rise in prevalence. Foot ulcerations, infections, Charcot neuroarthropathy, and peripheral arterial disease frequently result in gangrene and lower limb amputation. Consequently, foot disorders are leading causes of hospitalization for persons with diabetes and account for billion-dollar expenditures annually in the US. Although not all foot complications can be prevented, dramatic reductions in frequency have been achieved by taking a multidisciplinary approach to patient management. Using this concept, the authors present a clinical practice guideline for diabetic foot disorders based on currently available evidence, committee consensus, and current clinical practice. The pathophysiology and treatment of diabetic foot ulcers, infections, and the diabetic Charcot foot are reviewed. While these guidelines cannot and should not dictate the care of all affected patients, they provide evidence-based guidance for general patterns of practice. If these concepts are embraced and incorporated into patient management protocols, a major reduction in diabetic limb amputations is certainly an attainable goal.

Diabetic Foot Ulcers

When treating diabetic foot ulcers it is important to be aware of the natural history of the diabetic foot, which can be divided into five stages: stage 1, a normal foot; stage 2, a high risk foot; stage 3, an ulcerated foot; stage 4, an infected foot; and stage 5, a necrotic foot. This covers the entire spectrum of foot disease but emphasises the development of the foot ulcer as a pivotal event in stage 3, which demands urgent and aggressive management. Diabetic foot care in all stages needs multidisciplinary management to control mechanical, wound, microbiological, vascular, metabolic and educational aspects. Achieving good metabolic control of blood glucose, lipids and blood pressure is important in each stage, as is education to teach proper foot care appropriate for each stage. Ideally, it is important to prevent the development of ulcers in stages 1 and 2. In stage 1, the normal foot, it is important to encourage the use of suitable footwear, and to educate the patient to promote healthy foot care and footwear habits. In stage 2, the foot has developed one or more of the following risk factors for ulceration: neuropathy, ischaemia, deformity, swelling and callus. The majority of deformities can be accommodated in special footwear and as callus is an important precursor of ulceration it should be treated aggressively, especially in the neuropathic foot. In stage 3, ulcers can be divided into two distinct entities: those in the neuropathic foot and those in the neuroischaemic foot. In the neuropathic foot, ulcers commonly develop on the plantar surface of the foot and the toes, and are associated with neglected callus and high plantar pressures. In the neuroischaemic foot, ulcers are commonly seen around the edges of the foot, including the apices of the toes and back of the heel, and are associated with trauma or wearing unsuitable shoes. Ulcers in stage 3 need relief of pressure (mechanical control), sharp debridement and dressings (wound control), and neuroischaemic foot ulcers may need vascular intervention (vascular control). In stage 4, microbiological control is crucial and severe infections need intravenous antibacterial therapy, and urgent assessment of the need for surgical drainage and debridement. Without urgent treatment, severe infections will progress to necrosis. In stage 5, necrosis can be divided into wet and dry necrosis. Wet necrosis in neuropathic feet requires intravenous antibacterials and surgical debridement, and wet necrosis in neuroischaemic feet also needs vascular reconstruction. Aggressive management of diabetic foot ulceration will reduce the number of feet proceeding to infection and necrosis, and thus reduce the number of major amputations in diabetic patients.

Treatment for diabetic foot ulcers

People with diabetes develop foot ulcers because of neuropathy (sensory, motor, and autonomic deficits), ischaemia, or both. The initiating injury may be from acute mechanical or thermal trauma or from repetitively or continuously applied mechanical stress. Patients with clinically significant limb ischaemia should be assessed by a vascular surgeon to determine the need for angioplasty, stenting, or femorodistal bypass. When infection complicates a foot ulcer, the combination can be limb or life-threatening. Infection is defined clinically, but wound cultures reveal the causative pathogens. Tissue specimens are strongly preferred to wound swabs for wound cultures. Antimicrobial therapy should be guided by culture results, and should aim to cure the infection, not to heal the wound. Alleviation of the mechanical load on ulcers (off-loading) should always be a part of treatment. Neuropathic ulcers typically heal in 6 weeks with total contact casting, because it effectively relieves pressure at the ulcer site and enforces patient compliance. The success of other approaches to off-loading similarly depends on the patients' adherence to the effectiveness of pressure relief. Surgery to heal ulcers and prevent recurrence can include tenotomy, tendon lengthening, reconstruction, or removal of bony prominences. However, these procedures may result in secondary ulceration and other complications. Ulcer recurrence rates are high, but appropriate education for patients, the provision of posthealing footwear, and regular foot care can reduce rates of re-ulceration.