A. Biasibetti

Prevention of Pin Track Infection in External Fixation with Silver Coated Pins: Clinical and Microbiological Results

Pin tract infection is a frequent complication of external fixation; according to literature its frequency ranges from 2-30%. The recent introduction of silver coating of polymeric materials was found to decrease bacterial adhesion; its clinical use with Foley catheters and central venous catheters led to significant results. To verify the ability of the same silver coating to decrease the bacterial colonization on external fixation screws, a prospective randomized study was carried out on 24 male patients; a total of 106 screws were implanted in the lower limb to fix femoral or tibial diaphyseal fractures: 50 were coated with silver and 56 were commercially available stainless steel screws. Although the coated screws resulted in a lower rate of positive cultures (30.0%) than the uncoated screws (42.9%), this difference was not statistically significant (p = 0.243). The clinical behavior of the coated screws did not differ from that of the uncoated ones. Furthermore, the implant of silver-coated screws resulted in a significant increase in the silver serum level. These results led us to consider it ethically unacceptable to continue this investigation.

Glycopeptide Bone Penetration in Patients with Septic Pseudoarthrosis of the Tibia

Background and objective: In the treatment of bone infections, a major determinant of the clinical response is the active drug concentration at the infected site. Because of the high prevalence of meticillin (methicillin)-resistant staphylococci and enterococci, glycopeptides are widely used for the treatment of bone and joint infections, but data on their penetration into human bone are lacking. The aim of our study was to measure vancomycin and teicoplanin concentrations in infected human bone under steady-state conditions and verify their relationship with inflammatory markers, patient demographic characteristics and pharmacodynamic microbiological markers.Methods and patients: Twenty-seven adult orthopaedic patients undergoing surgical debridement for septic pseudoarthrosis of the tibia and receiving either intravenous vancomycin (Vancocina® 1 g twice daily) or teicoplanin (Targosid® 10 mg/kg/day) were studied from January 2004 to January 2008. Plasma and bone specimens were simultaneously collected during surgery for pharmacokinetic and microbiological assays at a variable interval after antimicrobial administration. Bone samples were dissected into cortical and cancellous bone, cleaned of soft tissues, crushed and eluted into phosphate buffer. Necrotic samples and sequestra were not analysed.Plasma and bone antimicrobial concentrations were measured by a validated method of high-performance liquid chromatography with UV detection, and bone/plasma concentration ratios were calculated. Cortical and cancellous bone area under the concentration-time curve (AUC) over 24 hours (AUC24) values were measured by the linear-log trapezoidal rule, using WinNonlin® software, and were compared with the minimum inhibitory concentrations (MICs) of the infecting agents.Results: For vancomycin, the mean ± SD concentrations were 2.66 ± 1.2 mg/L in cortical bone and 11.53 ± 7.8 mg/L in cancellous bone (corresponding to 20.67% and 89.39% of intraoperative plasma concentrations), and the mean ± SD tissue AUC24 values were 55.15 ± 25.26 h · mg/L for cortical bone and 299.16 ± 299.54 h · mg/L for cancellous bone. For teicoplanin, the mean ± SD concentrations were 2.01 ± 1.7 and 7.51 ± 7.0 mg/L in cortical and cancellous bone, respectively (12.35% and 48.6% of intraoperative plasma concentrations), and the mean ± SD teicoplanin tissue AUC24 values were 34.08 ± 23.6 h · mg/L and 155.17 ± 132.8 h · mg/L for cortical bone and cancellous bone, respectively. The mean vancomycin AUC24/MIC ratios were 215.02 for plasma, 47.14 for cortical bone and 268.95 for cancellous bone. The mean teicoplanin AUC24/MIC ratios were 336.48, 36.27 and 197.21 for plasma, cortical bone and cancellous bone, respectively.Conclusions: Bone penetration of both glycopeptides ranged from poor (<15%) to satisfactory (15–30%) in the cortical compartment, while it was far higher into the highly vascularized cancellous tissue. Vancomycin bone penetration was slightly higher than with teicoplanin, but the difference was not statistically significant. Higher bone concentrations were observed with higher inflammatory markers, possibly as a result of increased vascularization and vascular permeability under inflammatory conditions. Bone concentrations over the MIC and AUC/MIC ratios suggested that both glycopeptides achieve a satisfactory pharmacokinetic exposure in the cancellous bone, as far as Gram-positive pathogens are concerned. On the other hand, cortical bone exposure was suboptimal in most patients. Furthermore, as antimicrobial penetration may be affected by impaired blood supply, the role of radical surgical removal of purulent and necrotic tissues appears to be essential in order to shorten treatment duration and to reduce the risk of treatment failure.

Osteomyelitis Caused by Enterobacter cancerogenus Infection following a Traumatic Injury: Case Report and Review of the Literature

ABSTRACT We report a case of osteomyelitis caused by Enterobacter cancerogenus resistant to aminopenicillins in a 56-year-old male who had a motorcycle accident and suffered from multiple bone fractures with abundant environmental exposure. E. cancerogenus has rarely been associated with human infections, and its clinical significance remains unclear.

Ceftriaxone bone penetration in patients with septic non-union of the tibia

OBJECTIVES A main determinant of clinical response to antibiotic treatment is drug concentration at the infected site. Data on ceftriaxone (CFX) bone penetration are lacking. We measured CFX concentrations in infected bone to verify their relationship with pharmacodynamic microbiological markers. METHODS Eleven patients undergoing debridement for septic non-union of the tibia and receiving intravenous CFX were studied. Plasma and bone specimens were collected intraoperatively at a variable interval after CFX administration. Drug concentrations were measured by high-performance liquid chromatography with ultraviolet detection (HPLC-UV) method. RESULTS Bone samples were extracted at a mean of 3.3 h (range 1.5-8.0 h) since the start of CFX infusion. The mean±standard deviation intraoperative CFX plasma concentration was 128.4±30.8 mg/l; the corresponding bone concentrations were 9.6±3.4 mg/l (7.8%) in the cortical compartment and 30.8±8.6 mg/l (24.3%) in the cancellous compartment. The mean 24-h area under the concentration-time curve (AUC(24)) values were 176.8±62.2 h*mg/l in cortical bone and 461.5±106.8 h*mg/l in cancellous bone. The time above the minimum inhibitory concentration (T>MIC) was 24 h in all compartments. The estimated mean free AUC/MIC ratios and T>MIC were 140 and 24.4 h, respectively, in cancellous bone and 42.4 and 21 h, respectively, in cortical bone. CONCLUSIONS CFX bone penetration was poor (<15%) in the cortical compartment and satisfactory in the more vascularized cancellous bone. The T>MIC and AUC/MIC ratios suggest that CFX achieves a satisfactory pharmacokinetic exposure in cancellous bone as far as pathogens with a MIC of <0.5 are concerned. However, considering free drug concentrations, pharmacokinetic/pharmacodynamic targets may not be fully achieved in cortical bone. As antibiotic exposure can be suboptimal in the infected cortical compartment, and drug penetration may be impaired into necrotic bone and sequesters, a radical surgical removal of purulent and necrotic tissues appears essential to shorten treatment duration and to prevent treatment failures.