The role of beta-lactam/beta-lactamase inhibitors in the management of mixed infections

Variation in antibiotic treatment for diabetic patients with serious foot infections: a retrospective observational study

Background

Diabetic foot infections are common, serious, and diverse. There is uncertainty about optimal antibiotic treatment, and probably substantial variation in practice. Our aim was to document whether this is the case: A finding that would raise questions about the comparative cost-effectiveness of different regimens and also open the possibility of examining costs and outcomes to determine which should be preferred.

Methods

We used the Veterans Health Administration (VA) Diabetes Epidemiology Cohorts (DEpiC) database to conduct a retrospective observational study of hospitalized patients with diabetic foot infections. DEpiC contains computerized VA and Medicare patient-level data for VA patients with diabetes since 1998, including demographics, ICD-9-CM diagnostic codes, antibiotics prescribed, and VA facility. We identified all patients with ICD-9-CM codes for cellulitis/abscess of the foot and then sub-grouped them according to whether they had cellulitis/abscess plus codes for gangrene, osteomyelitis, skin ulcer, or none of these. For each facility, we determined: 1) The proportion of patients treated with an antibiotic and the initial route of administration; 2) The first antibiotic regimen prescribed for each patient, defined as treatment with the same antibiotic, or combination of antibiotics, for at least 5 continuous days; and 3) The antibacterial spectrum of the first regimen.

Results

We identified 3,792 patients with cellulitis/abscess of the foot either alone (16.4%), or with ulcer (32.6%), osteomyelitis (19.0%) or gangrene (32.0%). Antibiotics were prescribed for 98.9%. At least 5 continuous days of treatment with an unchanged regimen of one or more antibiotics was prescribed for 59.3%. The means and (ranges) across facilities of the three most common regimens were: 16.4%, (22.8%); 15.7%, (36.1%); and 10.8%, (50.5%). The range of variation across facilities proved substantially greater than that across the different categories of foot infection. We found similar variation in the spectrum of the antibiotic regimen.

Conclusions

The large variations in regimen appear to reflect differences in facility practice styles rather than case mix. It is unlikely that all regimens are equally cost-effective. Our methods make possible evaluation of many regimens across many facilities, and can be applied in further studies to determine which antibiotic regimens should be preferred.

Development of an assay for beta-lactam hydrolysis using the pH-dependence of enhanced green fluorescent protein

An assay has been developed utilizing the pH-dependent fluorescence of enhanced green fluorescent protein (EGFP). This photoprotein allows for the study of kinetic properties of hydrolytic enzymes based on the production of protons. As a model system, beta-lactamase, a well-characterized enzyme responsible for antibiotic resistance in many bacteria, was used. More specifically, EGFP and beta-lactamase were genetically fused using overlap extension PCR and incorporated into a bacterial expression vector. The vector was subsequently transformed into Escherichia coli, and the fusion protein was expressed and purified. beta-Lactamase catalyzes the hydrolysis of the beta-lactam ring of ampicillin. This causes a decrease in the local pH, which in turn changes the spectral properties of EGFP. This property was utilized to perform enzyme kinetic studies on the new fusion protein as well as on the beta-lactamase inhibitor, sulbactam. The assay can be used to evaluate substrates and inhibitors of beta-lactamase in a format that should be amenable to high-throughput screening.

Antibiotic prophylaxis in head and neck oncologic surgery: the role of gram-negative coverage

Many studies have elucidated the risk factors associated with peri-operative infection following head and neck cancer surgery (HNS), the implications of infection for total treatment cost, and the clinical benefits of successful antimicrobial prophylaxis. The most appropriate antibiotic use is achieved by focusing on patients with clean, contaminated wounds. Thereafter, the usefulness of an antibiotic agent depends on its antimicrobial spectrum, tolerability profile, and cost. Successful antimicrobial prophylaxis requires antimicrobial activity against gram-positive, gram-negative, and anaerobic organisms. The beta-lactam/beta-lactamase inhibitor combination, sulbactam-ampicillin, has just such an antimicrobial spectrum. A double-blind, randomized clinical trial, involving patients undergoing HNS, recorded a lower post-operative infection rate among patients receiving peri-operative sulbactam-ampicillin 0.5 g/1.0 g i.v. q6h compared with those receiving clindamycin 600 mg i.v. q6h (13.3 vs. 27.1%; P = 0.02). Culture of strains from infected individuals indicated a significantly lower proportion of gram-negative organisms for sulbactam-ampicillin than for clindamycin (32 vs. 81%; P < 0.05). There was a significant difference in the median duration of surgery between infected and non-infected individuals (8.5 vs. 5.9 h; P < 0.0001). These data support the use of sulbactam-ampicillin to reduce the incidence of post-operative infection following HNS.