Distribution of gentamicin from a Gentacoll sponge measured by in vivo microdialysis

Local Vancomycin Concentrations after Intra-articular Injection into the Knee Joint: An Experimental Porcine Study

Intra-articular injection of vancomycin may be an important antimicrobial prophylactic supplement to systemic administration in the prevention of prosthetic joint infections. In eight female pigs, 500 mg of diluted vancomycin was given by intra-articular injection into the knee joint. Microdialysis was used for dense sampling of vancomycin concentrations over 12 hours in the synovial fluid of the knee joint, and in the adjacent femoral and tibial cancellous bone and subcutaneous tissue. Venous blood samples were obtained as reference. The mean (standard deviation [SD]) peak drug concentration of vancomycin in the synovial fluid of the knee joint was 5,277 (5,668) μg/mL. Only one pig failed to reach a peak drug concentration above 1,000 μg/mL. The concentration remained high throughout the sampling interval with a mean (SD) concentration of 337 (259) μg/mL after 690 minutes. For all extraarticular compartments, the pharmacokinetic parameters (area under the concentration time-curve, peak drug concentration, and time to peak drug concentration) were comparable. The highest extraarticular mean (SD) peak drug concentration of 4.4 (2.3) μg/mL was found in subcutaneous tissue. An intra-articular injection of 500 mg diluted vancomycin was found to provide significant prophylactic mean concentrations for at least 12 hours in the synovial fluid of the knee joint. Correspondingly, the adjacent tissue and plasma concentrations were low but remained stable, signifying low risk of systemic toxic side effects and a slow release or uptake from the synovium to the systemic circulation.

Local concentrations of gentamicin obtained by microdialysis after a controlled application of a GentaColl sponge in a porcine model

Local treatment with gentamicin may be an important tool in the prevention and treatment of surgical site infections in high-risk procedures and patients. The aim of this study was to evaluate the pharmacokinetic profile of gentamicin in bone and surrounding tissue, released from a controlled application of a GentaColl sponge in a porcine model. In eight female pigs, a GentaColl sponge of 10 × 10 cm (1.3 mg gentamicin/cm² ) was placed in a cancellous bone cavity in the proximal tibia. Microdialysis was used for sampling of gentamicin concentrations over 48 hours from the cavity with the implanted GentaColl sponge, cancellous bone parallel to the cavity over and under the epiphyseal plate, cortical bone, the intramedullary canal, subcutaneous tissue, and the joint cavity of the knee. Venous blood samples were obtained as reference. The main finding was a mean peak drug concentration (95% CI) of gentamicin in the cancellous bone cavity containing the implanted GentaColl sponge of 11 315 (9049-13 581) μg/mL, persisting above 1000 μg/mL until approximately 40 hours after application. Moreover, the concentrations were low (<1 μg/mL) in the surrounding tissues as well as in plasma. The mean peak gentamicin concentration from the cancellous bone cavity after a controlled application of a GentaColl sponge was high and may be adequate for the prevention of biofilm formation. However, high MIC strains and uncontrolled application of the GentaColl sponge may jeopardize this conclusion.

Intra-articular Gentamicin-loaded PLA Microparticle Injection for the Treatment of Septic Arthritis in Rabbits

BACKGROUND

Because local delivery of drugs induces high concentrations, it could be helpful to apply these delivery systems to the treatment of septic arthritis by antibiotics. Thus, a gentamicin-loaded polymer was tested in a rabbit model of Staphylococcus aureus septic arthritis.

METHODS

Thirty New Zealand rabbits were split into five groups: A: infection only; B: infection and systemic gentamicin treatment; C: infection and unloaded polymer and systemic gentamicin treatment; D: infection and gentamicin-loaded polymer only; and E: no infection and unloaded polymer. After inducing nonlethal septic arthritis in the knee joint by injecting 10 colony-forming units (CFUs) of a strain of methicillin-sensitive S aureus in groups A, B, C, and D, rabbits were housed for 15 days, and then the joint capsules were removed and the remaining bacteria were counted. Bacterial load was expressed in CFUs per gram of synovial tissue. In group E, capsules were removed, and a pathologic examination was done.

RESULTS

At day 15, the bacterial load was 6 × 10, 2 × 10, 1.8 × 10, and 7 × 10 CFU/g of tissue for groups A, B, C, and D, respectively. Compared with the mean of groups A, B, and C, the bacterial load of group D was 4.94 units of log10 CFU/g lower than that of these groups. The bacterial load of group D was statistically significantly lower than that of the other three groups. Noticeably, two animals of group D had a nil bacterial count. In group E animals, a minimal foreign body reaction was observed around the polymer.

DISCUSSION

Gentamicin-containing microparticles were more efficient in reducing bacterial load than systemic injections of gentamicin and thus have an interesting role to play in the treatment of human arthritis. However, inserting microparticles in joints is not easy, and hydrogels might be a good alternative approach.

Cementless One-Stage Revision in Chronic Periprosthetic Hip Joint Infection. Ninety-One Percent Infection Free Survival in 56 Patients at Minimum 2-Year Follow-Up

BACKGROUND

Cementless 1-stage revision in chronic periprosthetic hip joint infections is limited evaluated. The purpose of this study was to evaluate a specific treatment protocol in this patient group.

METHODS

The study was performed as a multicenter, proof-of-concept, observational study with prospective data collection. Patients were treated with a cementless 1-stage revision according to the CORIHA protocol between 2009 and 2014. Fifty-six patients, McPherson type III-A/B-1/2, were enrolled with a mean follow-up time from the CORIHA procedure of 4 years (minimum of 2 years). The primary outcome was re-revision performed due to infection and was evaluated by competing risk analysis, with death and aseptic revision as competing events. All-cause mortality was evaluated by Kaplan-Meier survival analysis. Oxford Hip Score (OHS) was used as disease-specific patient-reported outcome measure.

RESULTS

The cumulative incidence of re-revision due to infection was 8.9% (confidence interval [CI] 3.2%-18.1%). The 1-year and 5-year survival incidence was 96% (CI 86%-99%) and 89% (CI 75%-95%). OHS at baseline was 19.9 (CI 17.3-22.6) and at 24-month follow-up 35.1 (CI 31.7-38.5). The mean change in OHS from baseline to 24-month follow-up was 11.8 points (CI 7.3; 16.3). Three patients had aseptic revision performed: two suffered periprosthetic fractures and one had stem subsidence. Failure analysis of the 5 reinfections did not detect a clear pattern as to the cause of failure.

CONCLUSION

We found that cementless 1-stage revision in chronic periprosthetic hip joint infections has low reinfection rates in selected patients and may be applicable as a first-line treatment.

Pharmacokinetics of single-dose cefuroxime in porcine intervertebral disc and vertebral cancellous bone determined by microdialysis

BACKGROUND

Pyogenic spondylodiscitis is associated with prolonged antimicrobial therapy and high relapse rates. Nevertheless, tissue pharmacokinetic studies of relevant antimicrobials in both prophylactic and therapeutic situations are still sparse. Previous approaches based on bone biopsy and discectomy exhibit important methodological limitations.

PURPOSE

The objective of this study was to assess the C3-C4 intervertebral disc (IVD), C3 vertebral body cancellous bone, and subcutaneous adipose tissue (SCT) pharmacokinetics of cefuroxime by use of microdialysis in a large animal model.

STUDY DESIGN

This was a single-dose, dense sampling large animal study of cefuroxime spine penetration.

METHODS

Ten female pigs were assigned to receive 1,500 mg of cefuroxime intravenously over 15 minutes. Measurements of cefuroxime were obtained from plasma, SCT, vertebral cancellous bone, and IVD for 8 hours thereafter. Microdialysis was applied for sampling in solid tissues.

RESULTS

For both IVD and vertebral cancellous bone, the area under the concentration curve from zero to the last measured value (AUC(0-last)) was significantly lower than that of free plasma. As estimated by the ratio of tissue AUC(0-last) to plasma AUC(0-last), tissue penetration (95% confidence interval) of cefuroxime was significantly incomplete for the IVD 0.78 (0.57; 0.99), whereas for vertebral cancellous bone 0.78 (0.51; 1.04) and SCT 0.94 (0.73; 1.15) it was not. The penetration of cefuroxime from plasma to the IVD was delayed, and the maximal concentration and the elimination of cefuroxime were also reduced compared with both SCT and vertebral cancellous bone. Because of this delay in elimination of cefuroxime, the time with concentrations above the minimal inhibitory concentration (T(>MIC)) was significantly longer in the IVD compared with the remaining compartments up to MICs of 6 µg/mL.

CONCLUSIONS

Microdialysis was successfully applied for serial assessment of the concentration of cefuroxime in the IVD and the vertebral cancellous bone. Penetration of cefuroxime from plasma to IVD was found to be incomplete and delayed, but because of a prolonged elimination, superior T(>MIC) was found in the IVD up to MICs of 6 µg/mL.

Continuous versus short-term infusion of cefuroxime: assessment of concept based on plasma, subcutaneous tissue, and bone pharmacokinetics in an animal model

The relatively short half-lives of most β-lactams suggest that continuous infusion of these time-dependent antimicrobials may be favorable compared to short-term infusion. Nevertheless, only limited solid-tissue pharmacokinetic data are available to support this theory. In this study, we randomly assigned 12 pigs to receive cefuroxime as either a short-term or continuous infusion. Measurements of cefuroxime were obtained every 30 min in plasma, subcutaneous tissue, and bone. For the measurements in solid tissues, microdialysis was applied. A two-compartment population model was fitted separately to the drug concentration data for the different tissues using a nonlinear mixed-effects regression model. Estimates of the pharmacokinetic parameters and time with concentrations above the MIC were derived using Monte Carlo simulations. Except for subcutaneous tissue in the short-term infusion group, the tissue penetration was incomplete for all tissues. For short-term infusion, the tissue penetration ratios were 0.97 (95% confidence interval [CI], 0.67 to 1.39), 0.61 (95% CI, 0.51 to 0.73), and 0.45 (95% CI, 0.36 to 0.56) for subcutaneous tissue, cancellous bone, and cortical bone, respectively. For continuous infusion, they were 0.53 (95% CI, 0.33 to 0.84), 0.38 (95% CI, 0.23 to 0.57), and 0.27 (95% CI, 0.13 to 0.48) for the same tissues, respectively. The absolute areas under the concentration-time curve were also lower in the continuous infusion group. Nevertheless, a significantly longer time with concentrations above the MIC was found for continuous infusion up until MICs of 4, 2, 2, and 0.5 μg/ml for plasma and the same three tissues mentioned above, respectively. For drugs with a short half-life, like cefuroxime, continuous infusion seems to be favorable compared to short-term infusion; however, incomplete tissue penetration and high MIC strains may jeopardize the continuous infusion approach.

Pharmacokinetics of cefuroxime in porcine cortical and cancellous bone determined by microdialysis

Traditionally, the pharmacokinetics of antimicrobials in bone have been investigated using bone biopsy specimens, but this approach suffers from considerable methodological limitations. Consequently, new methods are needed. The objectives of this study were to assess the feasibility of microdialysis (MD) for measuring cefuroxime in bone and to obtain pharmacokinetic profiles for the same drug in porcine cortical and cancellous bone. The measurements were conducted in bone wax sealed and unsealed drill holes in cortical bone and in drill holes in cancellous bone and in subcutaneous tissue. As a reference, the free and total plasma concentrations were also measured. The animals received a bolus of 1,500 mg cefuroxime over 30 min. No significant differences were found between the key pharmacokinetic parameters for sealed and unsealed drill holes in cortical bone. The mean ± standard error of the mean area under the concentration-time curve (AUC) values from 0 to 5 h were 6,013 ± 1,339, 3,222 ± 1086, 2,232 ± 635, and 952 ± 290 min · μg/ml for free plasma, subcutaneous tissue, cancellous bone, and cortical bone, respectively (P < 0.01, analysis of variance). The AUC for cortical bone was also significantly different from that for cancellous bone (P = 0.04). This heterogeneous tissue distribution was also reflected in other key pharmacokinetic parameters. This study validates MD as a suitable method for measuring cefuroxime in bone. Cefuroxime penetration was impaired for all tissues, and bone may not be considered one distinct compartment.

Elution kinetics, antimicrobial efficacy, and degradation and microvasculature of a new gentamicin-loaded collagen fleece

Management of bone and soft tissue infections generally includes surgical procedures as well as attendant treatment and prevention with gentamicin-loaded fleeces. Conventional gentamicin-containing collagen fleeces currently in use are strongly acidic and exhibit limited biocompatibility thereby adversely affecting wound healing. To improve the antibiotic delivery system, a new phosphate-buffered, gentamicin-loaded fleece with pH-neutral properties has been developed (Jason G). This study aimed at comparing the elution kinetics of gentamicin release and the antimicrobial efficacy of conventional fleeces with the newly developed fleece in vitro. In addition, degradation and microvasculature of implanted fleeces were examined in a rat model and assessed using histology, as well as detection of ED-1 and PECAM-expression using immunohistochemistry. We show that the phosphate-buffered fleeces have reduced release (p < 0.05) of the integrated gentamicin. However, all of the fleeces tested had a significant antimicrobial effect on the growth of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa strains (p < 0.01). Among the fleeces tested, the new Jason G fleece had the weakest but nevertheless sufficient antimicrobial effectiveness. Evaluation of the antibiotic effect in the prevention of an infection showed no differences between the applied fleeces. Following surgical implantation of fleece in the backs of Wistar rats we observed, on day 5 after implantation, an increase in cell infiltration and microvascularization with the phosphate-buffered fleece as compared with conventional fleeces, which show necrotic cells on their surface. Unlike the acidic fleeces, on day 15 after implantation the pH-neutral fleece was resorbed widely. Here, we show that the new, pH-neutral, gentamicin-containing fleece Jason G exhibits good overall antimicrobial effectiveness against both gram-positive and gram-negative bacteria in vitro with improved degradation properties and microvasculature formation in vivo.

A pilot study testing whether concentrations of levofloxacin in interstitial space fluid of soft tissues may serve as a surrogate for predicting its pharmacokinetics in lung

Recent observations indicate that pharmacokinetics of beta-lactam antibiotics in the lung can be predicted by the use of concentration versus time profiles in peripheral soft tissues. If this observation is transferred to other classes of antimicrobials, measurement of antimicrobial concentrations in peripheral tissues would enable prediction of the pharmacokinetics of antimicrobials at the site of the respiratory tract infection. We set out to test the hypothesis that concentrations of the fluoroquinolone levofloxacin in the respiratory tract can be predicted on the basis of knowledge of its pharmacokinetics in peripheral soft tissues. After administration of a single intravenous dose of 500mg of levofloxacin, microdialysis was used to describe the concentration versus time profiles of levofloxacin in the interstitial space fluid of lung tissue of patients (n=5) undergoing elective lung surgery. These data were compared with the concentration versus time courses in the interstitial space fluid of skeletal muscle and subcutaneous adipose tissue of healthy volunteers (n=7). The median AUC(0-infinity) of free levofloxacin in lung (2267mg x min/L, 1980-2355) was about 2-fold and 1.5-fold lower compared with skeletal muscle (4381mg x min/L, range 1720-8195) and adipose tissue (3492mg x min/L, range 1323-6420) of healthy controls, respectively. Concentrations in the interstitial space fluid of the lung were descriptively lower compared with corresponding concentrations in peripheral soft tissues. This is in contrast to previous observations made for the class of beta-lactam antibiotics, and indicates that pharmacokinetics of levofloxacin derived from soft tissues may not be used uncritically for prediction of levofloxacin concentrations in the interstitium of the lung.

Prophylaxis and treatment of implant-related infections by local application of antibiotics

Despite the improvement in surgical technique and implant design in orthopedic and trauma surgery, implant-related infections are still a challenging problem for surgeons. The use of local prophylaxis to avoid infection, such as antibiotic-loaded cement in arthroplasty, gentamicin PMMA beads and gentamicin-collagen sponge in trauma surgery, and antibacterial coating of metal implants, is discussed in the first part of this article. The second part discusses the role of local antibiotics such as gentamicin PMMA beads, and gentamicin-collagen and antibiotic-loaded cement spacers in treating implant-related infections.