Intra-articular pharmacokinetics of a gentamicin impregnated collagen sponge in the canine stifle: an experimental study

Pharmacokinetic study of local and systemic gentamicin concentrations after subcutaneous implantation of a gentamicin-impregnated collagen sponge in dogs

This study evaluated the pharmacokinetics of commercial gentamicin-impregnated collagen sponges (GICS) applied subcutaneously in dogs. In six healthy beagles, an 11 ×6 cm subcutaneous pocket was created, a folded 10×10 cm GICS was inserted, and saline was injected to mimic a seroma. Wound fluid samples were aspirated, and the gentamicin concentration was determined. Simultaneously, blood samples were collected to evaluate the corresponding systemic gentamicin concentration. All samples were collected before and 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 18, 24, 36, 48, 72, 96, 120, and 168 hours after GICS placement. The local Cmax of gentamicin was reached after 0.5 hours (range, 0.5-1.0 hours) post-implantation in 5/6 dogs at a median concentration of 2053.3 µg/mL (range, 918.0-2791.9 µg/mL). Whitin 24 hours, the local concentration dropped below the MIC for Staphylococcus sp. (4 µg/mL) in 5/6 dogs. Plasma Cmax was achieved at a median of 1.2 hours post-implantation (range, 1.0-2.0 hours) and reached a median concentration of 10.3 µg/mL (range, 8.8-18.03 µg/mL). After 6 hours, the gentamicin concentration in the plasma was below 4 µg/mL in all dogs. The GICS provided a high local concentration of gentamicin in a short time with a local Cmax:MIC ratio of 513:1, largely sufficient to eliminate susceptible bacteria, including methicillin-resistant Staphylococcus pseudintermedius (MRSP) and Pseudomonas sp., in a clinical setting. The repeated administration of saline in the present study seemed to have induced a quicker gentamicin release from the GICS than described in previous studies that typically dealt with "drier" wounds.

Pseudomonas aeruginosa biofilm killing beyond the spacer by antibiotic-loaded calcium sulfate beads: an in vitro study

Introduction: Bacterial biofilms are an important virulence factor in chronic periprosthetic joint infection (PJI) and other orthopedic infection since they are highly tolerant to antibiotics and host immunity. Antibiotics are mixed into carriers such as bone cement and calcium sulfate bone void fillers to achieve sustained high concentrations of antibiotics required to more effectively manage biofilm infections through local release. The effect of antibiotic diffusion from antibiotic-loaded calcium sulfate beads (ALCS-B) in combination with PMMA bone cement spacers on the spread and killing of Pseudomonas aeruginosa Xen41 (PA-Xen41) biofilm was investigated using a “large agar plate” model scaled for clinical relevance. Methods: Bioluminescent PA-Xen41 biofilms grown on discs of various orthopedic materials were placed within a large agar plate containing a PMMA full-size mock “spacer” unloaded or loaded with vancomycin and tobramycin, with or without ALCS-B. The amount of biofilm spread and log reduction on discs at varying distances from the spacer was assessed by bioluminescent imaging and viable cell counts. Results: For the unloaded spacer control, PA-Xen41 spread from the biofilm to cover the entire plate. The loaded spacer generated a 3 cm zone of inhibition and significantly reduced biofilm bacteria on the discs immediately adjacent to the spacer but low or zero reductions on those further away. The combination of ALCS-B and a loaded PMMA spacer greatly reduced bacterial spread and resulted in significantly greater biofilm reductions on discs at all distances from the spacer. Discussion: The addition of ALCS-B to an antibiotic-loaded spacer mimic increased the area of antibiotic coverage and efficacy against biofilm, suggesting that a combination of these depots may provide greater physical antibiotic coverage and more effective dead space management, particularly in zones where the spread of antibiotic is limited by diffusion (zones with little or no fluid motion).

Temperature-responsive PNDJ hydrogels provide high and sustained antimicrobial concentrations in surgical sites

Local antimicrobial delivery is a promising strategy for improving treatment of deep surgical site infections (SSIs) by eradicating bacteria that remain in the wound or around its margins after surgical debridement. Eradication of biofilm bacteria can require sustained exposure to high antimicrobial concentrations (we estimate 100-1000 μg/mL sustained for 24 h) which are far in excess of what can be provided by systemic administration. We have previously reported the development of temperature-responsive hydrogels based on poly(N-isopropylacrylamide-co-dimethylbutyrolactone acrylate-co-Jeffamine M-1000 acrylamide) (PNDJ) that provide sustained antimicrobial release in vitro and are effective in treating a rabbit model of osteomyelitis when instilled after surgical debridement. In this work, we sought to measure in vivo antimicrobial release from PNDJ hydrogels and the antimicrobial concentrations provided in adjacent tissues. PNDJ hydrogels containing tobramycin and vancomycin were administered in four dosing sites in rabbits (intramedullary in the femoral canal, soft tissue defect in the quadriceps, intramuscular injection in the hamstrings, and intra-articular injection in the knee). Gel and tissue were collected up to 72 h after dosing and drug levels were analyzed. In vivo antimicrobial release (43-95% after 72 h) was markedly faster than in vitro release. Drug levels varied significantly depending on the dosing site but not between polymer formulations tested. Notably, total antimicrobial concentrations in adjacent tissue in all dosing sites were sustained at estimated biofilm-eradicating levels for at least 24 h (461-3161 μg/mL at 24 h). These results suggest that antimicrobial-loaded PNDJ hydrogels are promising for improving the treatment of biofilm-based SSIs.

Determination of Tobramycin and Vancomycin Exposure Required to Eradicate Biofilms on Muscle and Bone Tissue In Vitro

Background: Bacterial biofilms cause chronic orthopaedic infections. Surgical debridement to remove biofilm can be ineffective without adjuvant local antimicrobials because undetected biofilm fragments may remain in the wound and reestablish the infection if untreated. However, the concentrations and duration of antimicrobial exposure necessary to eradicate bacteria from clinical biofilms remain largely undefined. In this study, we determined the minimum biofilm eradication concentration (MBEC) of tobramycin and vancomycin for bacterial biofilms grown on bone and muscle in vitro. Methods: Biofilms of pathogens found in musculoskeletal infections (S. aureus, S. epidermidis, E. faecalis, P. aeruginosa, and E. coli) were established for 72 hr on rabbit muscle and bone specimens in vitro and characterized by SEM imaging and CFU counts. Biofilm-covered tissue specimens were exposed to serial log2 dilutions (4000-31.25 µg/mL) of tobramycin, vancomycin, or a 1:1 combination of both drugs for 6, 24, or 72 hr. Tissues were subcultured following antimicrobial exposure to determine bacterial survival. The breakpoint concentration with no surviving bacteria was defined as the MBEC for each pathogen-antimicrobial-exposure time combination. Results: All tested pathogens formed biofilm on tissue. Tobramycin/vancomycin (1:1) was the most effective antimicrobial regimen with MBEC on muscle (10/10 pathogens) or bone (7/10 pathogens) generally in the range of 100-750 µg/mL with 24 or 72 hr exposure. MBEC decreased with exposure time for 53.3% of biofilms between 6 and 24 hr, 53.3% of biofilms between 24 and 72 hr, and for 76.7% of biofilms between 6 and 72 hr. MBECs on bone were significantly higher than corresponding MBECs on muscle tissue (p < 0.05). In most cases, tissue MBECs were lower compared to previously published MBECs for the same pathogens on polystyrene tissue-culture plates. Conclusions: The majority of MBECs for orthopaedic infections on bone and muscle are on the order of 100-750 µg/mL of vancomycin+tobramycin when sustained for at least 24 hr, which may be clinically achievable using high-dose antimicrobial-loaded bone cement (ALBC).

A review of local antibiotic implants and applications to veterinary orthopaedic surgery

In the face of increasing incidence of multidrug resistant implant infections, local antibiotic modalities are receiving increased attention for both infection prophylaxis and treatment. Local antibiotic therapy that achieves very high antibiotic drug concentrations at the site of the implant may represent an avenue for treatment of biofilmforming bacterial pathogens. Randomized controlled trials in human patients have demonstrated an infection risk reduction when antibiotic-impregnated cement is used for infection prophylaxis in implanted joint prostheses, and when a gentamicin-impregnated collagen sponge is used for infection prophylaxis in midline sternotomy. The other modalities discussed have for the most part yet to be evaluated in randomized controlled trials in veterinary or human patients. In general, the in vivo pharmacokinetics and appropriate dosing profiles for local antibiotic modalities have yet to be elucidated. Toxicity is possible, and attention to the dose applied is warranted.

Intra-articular implantation of gentamicin impregnated collagen sponge causes joint inflammation and impaired renal function in dogs

OBJECTIVE

Gentamicin impregnated collagen sponge (GICS) can be used to treat intra-articular surgical site infections. High local concentrations of gentamicin can be reached for short periods; however the collagen vehicle may persist for much longer periods. We wished to determine the effect of sponge implantation on joint inflammation and renal function.

METHODS

Eighteen medium sized mixed breed research dogs of hound type were randomized to two groups; arthroscopic implantation of GICS at gentamicin dose = 6 mg/kg (n = 9) or sham operation (n = 9). Endpoints consisted of joint inflammation measured by synovial fluid cell counts and cytokine concentrations; lameness measured by force plate asymmetry indices; and renal function measured by glomerular filtration rate (GFR) study. The prevalence of lesions associated with aminoglycoside nephrotoxicity was assessed by renal biopsy and transmission electron microscopy.

RESULTS

Gentamicin impregnated collagen sponge implantation caused joint inflammation (p <0.01), lameness (p = 0.04), and decreased GFR (p = 0.04). No difference was observed in the prevalence of renal lesions on biopsy between the treatment and control groups (p = 0.49).

CLINICAL SIGNIFICANCE

Gentamicin impregnated collagen sponge implantation causes joint inflammation and lameness as well as GFR reductions at the dose assessed. Gentamicin impregnated collagen sponge are not recommended for intra-articular implantation in dogs.