Sandra G. McLaren

The treatment of experimental osteomyelitis by surgical debridement and the implantation of calcium sulfate tobramycin pellets.

Calcium sulfate was used as a biodegradable delivery system for the administration of antibiotics in musculoskeletal infection. New Zealand white rabbits were infected with Staphylococcus aureus, debrided, and randomized to one of four treatment groups: calcium sulfate pellets with 10% tobramycin sulfate, placebo calcium sulfate pellets and IM tobramycin, placebo calcium sulfate pellets, or debridement. Serum and wound exudate tobramycin concentrations and serum calcium levels were measured. Radiographs, cultures, and histology were analyzed for efficacy and treatment. Rabbits treated with 10% tobramycin sulfate pellets showed a significantly higher eradication of infection (11/13) than rabbits treated with debridement only (5/12), placebo pellets and IM tobramycin (5/14), or placebo pellets (3/13). In the group receiving 10% tobramycin sulfate pellets, serum tobramycin concentrations peaked 3 h post‐operatively at 5.87 μg/ml and were non‐detectable after day 1. In the group receiving placebo pellets and IM tobramycin, serum concentrations peaked at 7.82 μg/ml 1 h post‐operatively, fell to 6.12 μg/ml on day 2, and averaged 4.18 μg/ml for the remainder of the treatment period. The wound exudate tobramycin concentrations in the animals treated with tobramycin sulfate pellets peaked at 11.9 mg/ml on day 1 and dropped to 2.5 μg/ml on day 7. There was no significant difference in the serum calcium levels in any of the treatment groups. Calcium sulfate containing tobramycin sulfate has potential utility as a biodegradable local antibiotic delivery system in the treatment of musculoskeletal infections.© 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.

Detecting bacterial colonization of implanted orthopaedic devices by ultrasonication.

Glycocalyx-producing bacteria have been observed on orthopaedic devices that were removed for reasons other than infection. It has been suggested that the bacteria adhere to foreign surfaces within a biofilm and elude standard culture techniques. The authors adapted previously used ultrasonication protocols that disrupt the surface biofilm before culturing removed orthopaedic devices from patients without clinical evidence of infection. Patients having revision total joint arthroplasty of the hip or knee who lacked current or prior clinical evidence of infection were studied prospectively. During surgery, the femoral component and a corresponding control femoral implant were placed in separate sterile bags of saline. The implant and saline combination was placed in an ultrasonication bath for 30 minutes at 60 Hz. The saline solution was passed through a 0.45-μm pore filter, and the filter residue was cultured on sheep blood agar. None of the 21 implants yielded positive culture on routine microbiologic testing. However, using the ultrasonication protocol, a coagulase-negative Staphylococcus grew from one of the removed implants. Numerous total joint implant failures that are attributed to aseptic loosening may be a result of subclinical infection from bacteria within a biofilm. The current study supports the concept that biofilm-protected bacterial colonization of implants may occur without overt signs of infection and ultrasonication can be used to enhance identification of these bacteria.

Xylitol and glycine fillers increase permeability of PMMA to enhance elution of daptomycin.

The elution of antibiotics from hand mixed antibiotic-laden polymethylmethacrylate (PMMA) must be increased to achieve clinical performance equivalent to commercially manufactured antibiotic beads (not available in the USA) in the management of musculoskeletal infections. Adding fillers such as glycine and dextran to polymethylmethacrylate increases the elution of antibiotics from antibiotic-laden PMMA. We propose xylitol, a naturally occurring sweetener with direct antibiofilm properties, as a filler material. To compare the efficacy of xylitol and glycine as fillers on the elution of antibiotics from PMMA, elution studies were performed on mixtures of Palacos® polymethylmethacrylate and daptomycin (1 gm) with xylitol or glycine as the filler (28 g). Xylitol and glycine enhanced the daptomycin activity eluted from the polymethylmethacrylate. Xylitol was more effective than glycine, having a greater increase in daptomycin release at all data points; on day one xylitol increased the elution of daptomycin 2.67 times whereas glycine increased it 1.78 times also on day one. The eluant concentration of daptomycin remained higher longer for xylitol; 3.90 μg/mL for xylitol versus 2.25 μg/mL for glycine on day 9. Xylitol is inexpensive and readily available. It can be hand mixed with PMMA, and is more effective than glycine as a filler to enhance daptomycin release. Considering possible antibiofilm activity, xylitol may be a more advantageous choice.

The effect of glycine filler on the elution rate of gentamicin from acrylic bone cement: a pilot study.

Elution of antibiotics from acrylic bone cement (polymethylmethacrylate [PMMA]) is dependent on the access of fluid to the depths of the cement that contains the antibiotic. Commercially prepared antibiotic beads that are porous have higher elution rates than hand-mixed, nonporous antibiotic PMMA mixtures. To increase the elution of gentamicin from hand-mixed PMMA, glycine was added as a filler to produce porosity. Elution of gentamicin from the antibiotic PMMA-glycine mixture increased with increasing amounts of glycine. With 3.6 g gentamicin powder and 14 g of crystalline glycine per batch of Palacos PMMA, the elution of gentamicin from the PMMA at 2 days was, similar to the previously documented elution of gentamicin from commercially prepared porous Septopal PMMA beads. With further investigation it may be possible to identify a specific filler and a volume of filler that can be hand mixed in antibiotic PMMA to produce the elution behavior that is needed for specific clinical requirements.

The effect of sampling method on the elution of tobramycin from calcium sulfate.

Release rate is a critical property of all drug delivery vehicles, including antibiotic-laden bioerodibles. In vitro elution studies, used to evaluate release rates, use different sampling methods, including changing the entire amount of buffer and partial exchanges each day. Two groups of 10% calcium sulfate-tobramycin pellets were eluted in 20 mL of buffer for 30 days. Group I had 5 mL of buffer withdrawn and replaced daily whereas Group II had the entire 20 mL of buffer changed daily. The results show that the complete exchange method caused a significantly faster release of antibiotic than the partial exchange method. In the complete exchange group, greater than 50% of the tobramycin was released by 24 hours, whereas in the partial exchange group, 50% of the antibiotic was not released until Day 6. The two methods of sampling used to evaluate this bioerodible material provide data that allow the user to anticipate how the material will function in relatively inert and volatile environments. The method used to sample the elution of antibiotics from bioerodible materials affects the amount of antibiotic eluted. It therefore is important to know the method of sampling when making a decision to use a bioerodible material to deliver antibiotics locally.

Particle size of fillers affects permeability of polymethylmethacrylate.

Particulate soluble filler added to polymethylmethacrylate increases its permeability, leading to increased elution. We asked whether particle size affects permeability and elution rate associated with a given volume fraction of filler. Permeability of filler-loaded PMMA was measured in 9 mm rods with a 32% volume fraction of four particle sizes (106 μm, 212 μm, 425 μm, 850 μm) and two filler materials (sucrose and xylitol) using a modified phenolphthalein-sodium hydroxide technique, which allowed quantitative serial observation on the same specimens. Fluid penetration was faster for larger particle sizes. The elution rate was greater for smaller particle sizes on qualitative visual assessment. Sucrose fillers were not different from xylitol fillers independent of particle size. For the volume fraction of 32%, larger particles lead to larger caliber porosity, less pore intercon nectivity, and faster fluid penetration. Smaller size particles lead to smaller caliber porosity, greater pore interconnectivity, smaller areas between the pores with no fluid penetration and greater increase in the effective surface area causing a greater elution rate.

Sucrose, xylitol, and erythritol increase PMMA permeability for depot antibiotics

Release of antibiotics from antibiotic-loaded PMMA is dependent on its permeability. Loading PMMA with soluble particulate filler has been proposed to increase permeability and antibiotic release for beads and spacers. We therefore assessed particulate sucrose, xylitol, and erythritol as fillers to increase the permeability and elution kinetics of filler-loaded PMMA. Based on lower solubility, we hypothesized that erythritol would not enhance permeability and elution as much as xylitol and sucrose. We made filler-loaded PMMA beads with each of the three fillers combined with phenolphthalein, and soaked in 0.1% NaOH solution. Permeability was assessed qualitatively by relative depth of phenolphthalein color change caused by penetration of NaOH solution into subsequently split beads. Elution was quantitatively assessed by spectrophotometric light absorption measurements of the eluent. Fluid penetration reached the center of 7-mm beads by day 15, similar for all three materials. Elution of phenolphthalein was greater for xylitol than for the other two materials. Particulate sucrose, xylitol, and erythritol fillers increase PMMA permeability and elution kinetics but relative solubility did not determine the relative degree of enhancement of permeability and elution by these materials.

Optimized Elution of Daptomycin from Polymethylmethacrylate Beads

ABSTRACT We demonstrate that xylitol can be added to polymethylmethacrylate (PMMA) bone cement to enhance the elution of daptomycin in terms of both the peak and sustained release of antibiotic. We also demonstrate that a PMMA-xylitol formulation optimized for daptomycin can be used to enhance the elution of both vancomycin and gentamicin.

Chitosan coating to enhance the therapeutic efficacy of calcium sulfate-based antibiotic therapy in the treatment of chronic osteomyelitis

We demonstrate that coating calcium sulfate with deacetylated chitosan enhances the elution profile of daptomycin by prolonging the period during which high concentrations of antibiotic are released. Coatings reduced initial bolus release of daptomycin by a factor of 10 to approximately 1000 µg/ml, and levels remained above 100 µg/ml for up to 10 days. Chitosan-coated and uncoated calcium sulfate implants with and without 15% daptomycin were evaluated in an experimental model of staphylococcal osteomyelitis through bacteriology scores, radiology, histopathology, and Gram staining. Significant reduction in bacteriology scores was observed for implants containing daptomycin and coated with chitosan compared with all the other groups. We confirm that the use of chitosan-coated calcium sulfate beads for local antibiotic delivery can be correlated with an improved therapeutic outcome following surgical debridement in the treatment of chronic osteomyelitis.

Use of Xylitol To Enhance the Therapeutic Efficacy of Polymethylmethacrylate-Based Antibiotic Therapy in Treatment of Chronic Osteomyelitis

ABSTRACT Using a rabbit model of postsurgical osteomyelitis, we demonstrate that incorporation of xylitol into polymethylmethacrylate (PMMA) bone cement enhances the elution of daptomycin under in vivo conditions. We also demonstrate that this can be correlated with an improved therapeutic outcome in the treatment of a chronic bone infection following surgical debridement.