Bone grafts as vancomycin carriers in local therapy of resistant infections

Recent advances in the local antibiotics delivery systems for management of osteomyelitis

Chronic osteomyelitis is a challenging disease due to its serious rates of mortality and morbidity while the currently available treatment strategies are suboptimal. In contrast to the adopted systemic treatment approaches after surgical debridement in chronic osteomyelitis, local drug delivery systems are receiving great attention in the recent decades. Local drug delivery systems using special carriers have the pros of enhancing the feasibility of penetration of antimicrobial agents to bone tissues, providing sustained release and localized concentrations of the antimicrobial agents in the infected area while avoiding the systemic side effects and toxicity. Most important, the incorporation of osteoinductive and osteoconductive materials in these systems assists bones proliferation and differentiation, hence the generation of new bone materials is enhanced. Some of these systems can also provide mechanical support for the long bones during the healing process. Most important, if the local systems are designed to be injectable to the affected site and biodegradable, they will reduce the level of invasion required for implantation and can win the patients’ compliance and reduce the healing period. They will also allow multiple injections during the course of therapy to guard against the side effect of the long-term systemic therapy. The current review presents different available approaches for delivering antimicrobial agents for the treatment of osteomyelitis focusing on the recent advances in researches for local delivery of antibiotics.

HIGHLIGHTS

Chronic osteomyelitis is a challenging disease due to its serious mortality and morbidity rates and limited effective treatment options.

Local drug delivery systems are receiving great attention in the recent decades.

Osteoinductive and osteoconductive materials in the local systems assists bones proliferation and differentiation

Local systems can be designed to provide mechanical support for the long bones during the healing process.

Designing the local system to be injectable to the affected site and biodegradable will reduces the level of invasion and win the patients’ compliance.

Use of Vancomycin Mixed Bone Graft and Vancomycin Mixed Saline Wash Before Wound Closure Reduces the Rate of Infection in Lumbar Spine Fusion Surgery

This study aims to evaluate whether surgical site vancomycin mixed in bone grafts and local vancomycin mixed in normal saline wash before wound closure decrease the infection rates in patients undergoing lumbar spinal instrumentation and posterolateral fusion. A retrospective study was performed on cases between 2017 and 2019, who underwent lumbar spine instrumentation and posterolateral fusion for lumbar canal stenosis or listhesis. The routine prophylactic procedures were performed in all patients as per institutional protocol. Patients' records were analysed and categorised into two groups, the vancomycin group (VG), where vancomycin mixed in bone graft and normal saline wash was used at the surgical site, and the control group (CG), where vancomycin was not used. The study included 63 patients, 31 in VG and 32 in CG. There is no statistical difference in age, sex, and diabetes mellitus in both groups. A total of seven cases were infected, six in CG (6/32) and one in VG (1/31). Out of six infections in CG, three patients had diabetes and four infected cases underwent surgery for debridement. In VG, the only single case got infected and treated with intravenous antibiotics. We found that the use of vancomycin added to the bone graft and normal saline in posterior lumbar spinal instrumentation and posterolateral fusion is associated with significantly lower rates of infection (p value=0.049).

Antimicrobial efficacy and activity perseverance in arthroplasty of calcium sulfate beads containing vancomycin prepared ahead of time and stored in ready-to-use formula

The use of local therapy with antibiotics in a suitable carrier is essential in the treatment and prevention of infections in orthopedic surgery and traumatology. In our orthopedic surgery department, a synthetic calcium sulfate hemihydrate (CaSO₄·½H₂O) is used as an antibiotic carrier, enabling the application of most types of intravenous antibiotics in the form of powder and liquid. This type of carrier with antibiotics is prepared in the theater during the procedure. During a surgical procedure, a small dead space is created (hand and foot area), which must be filled with an antibiotic carrier, and the situations arise where a large amount of the carrier is not used and thrown away. Therefore, we verified the efficacy of vancomycin in the pre-prepared carrier by an orientation microbiological method and by measuring the concentrations of the vancomycin released in active form and its two crystalline degradation products. Based on the agar diffusion test, we did not measure any difference in the effectiveness of the antibiotic in the carrier after its 12-day storage. Although vancomycin concentrations decreased by approximately 32% at the end of 12 days of storage, the concentrations of the released active form of vancomycin are many times higher than the minimum inhibitory concentrations for resistant strains of Staphylococcus aureus. Thus, the calcium sulfate carrier with vancomycin can be prepared several days in advance before its application, certainly up to 12 days.

Vancomycin and its crystalline degradation products released from bone grafts and different types of bone cement

Vancomycin is often used in orthopedic surgery as a local prophylaxis of bacterial infection. The aim of this work was to compare the release of vancomycin and its biologically inactive crystalline degradation products (CDP-1) during in vitro experiments from different types of local antibiotic delivery systems (bone grafts and bone cements). The concentrations of vancomycin and its crystalline degradation products were determined by high-performance liquid chromatography. Each experiment was performed in a phosphate buffer solution over 21 days. Morselized bone grafts, synthetic bone cements Palacos and Copal, and synthetic bone grafts were tested as local carriers of vancomycin. The highest concentration approximately 670 mg/L of vancomycin was released from synthetic bone grafts Actifuse. Even after 21 days, the concentration of vancomycin was still above the minimum inhibitory concentration (MIC). The maximum concentration of vancomycin released in two experiments with human bone grafts exceeded 600 mg/L during the first day and was still above MIC level 21 days later when the experiment was concluded. By comparing the synthetic bone cements Palacos and Copal, Copal had the average maximum concentration of only 32.4 mg/L and Palacos 35.7 mg/L. The concentration of vancomycin fell below the MIC for vancomycin-resistant Staphylococcus aureus (VRSA) on the seventh day with Palacos and the ninth day with Copal. This study showed the insufficient concentration of released vancomycin from synthetic bone cements at the end of the experiment. For improvement of local prophylaxis, it would be beneficial to increase the amount of vancomycin in bone cements.

Current Insights in the Application of Bone Grafts for Local Antibiotic Delivery in Bone Reconstruction Surgery

Introduction: Bone implant related infection is still one of the biggest challenges in bone and joint surgery. Antibiotic impregnated bone grafts seem to be promising in both treatment and prevention of these infections. However, great variance in methodology predominates this field of research. This paper gives an overview of the published literature.

Methods: The PRISMA-flowchart was used as protocol for article selection. Medline was searched and articles were selected in accordance with predetermined exclusion criteria.

Results: Forty-eight articles were included in the synthesis. Topics including bone graft type, manipulations of the graft, elution profile, bacterial inhibition, osteotoxicity, incorporation, special impregnation methods, clinical use and storage were investigated.

Therapeutically, high initial levels seem appropriate for biofilm eradication. A single stage procedure in the treatment of bone implant related infection seems feasible. Prophylactically, the literature indicates a reduction of postoperative infections when using antibiotic impregnated bone grafts.

Conclusion: Bone grafts are a suitable carrier for local antibiotic application both therapeutically and prophylactically.

Vancomycin-bearing synthetic bone graft delivers rhBMP-2 and promotes healing of critical rat femoral segmental defects

BACKGROUND

Bone grafts simultaneously delivering therapeutic proteins and antibiotics may be valuable in orthopaedic trauma care. Previously, we developed a poly(2-hydroxyethyl methacrylate)-nanocrystalline hydroxyapatite (pHEMA-nHA) synthetic bone graft that, when preabsorbed with 400-ng rhBMP-2/7, facilitated the functional repair of critical-size rat femoral defects. Recently, we showed that pHEMA-nHA effectively retains/releases vancomycin and rhBMP-2 in vitro. The success of such a strategy requires that the incorporation of vancomycin does not compromise the structural integrity of the graft nor its ability to promote bone healing.

QUESTIONS/PURPOSES

(1) To evaluate the ability of pHEMA-nHA-vancomycin composites in combination with 3-µg rhBMP-2 to repair 5 mm rat femoral segmental defects, and (2) To determine if the encapsulated vancomycin impairs the graft/rhBMP-2-assisted bone repair.

METHODS

pHEMA-nHA-vancomycin, pHEMA-nHA, or collagen sponge control with/without 3-µg rhBMP-2 were press-fit in 5 mm femoral defects in SASCO-SD male rats (289-300 g). Histology, microcomputed tomography, and torsion testing were performed on 8- and 12-week explants to evaluate the extent and quality of repair. The effect of vancomycin on the temporal absorption of endogenous BMP-2 and stromal cell-derived factor-1 was evaluated by immunohistochemistry. These factors are important for bone healing initiation and stem cell recruitment, respectively.

RESULTS

Partial bridging of the defect with bony callus by 12 weeks was observed with pHEMA-nHA-vancomycin without rhBMP-2 while full bridging with substantially mineralized callus and partial restoration of torsional strength was achieved with 3-µg rhBMP-2. The presence of vancomycin changed the absorption patterns of endogenous proteins on the grafts, but did not appear to substantially compromise graft healing.

CONCLUSIONS

The composite pHEMA-nHA-vancomycin preabsorbed with 3-µg rhBMP-2 promoted repair of 5 mm rat femoral segmental defects. With the sample sizes applied, vancomycin encapsulation did not appear to have a negative effect on bone healing.

CLINICAL RELEVANCE

pHEMA-nHA-vancomycin preabsorbed with rhBMP-2 may be useful in the repair of critical-size long bone defects prone to infections.

Increased release time of antibiotics from bone allografts through a novel biodegradable coating

The use of bone allografts is contraindicated in septic revision surgery due to the high risk of graft reinfection. Antibiotic release from the graft may solve the problem and these combinations can theoretically be used for prevention or even therapy of infection. The present study investigated whether amoxicillin, ciprofloxacin, and vancomycin alone or in combination with chitosan or alginate are suitable for short-term or long-term bone coating. Human bone allografts were prepared from femoral head and lyophilized. Antibiotic coating was achieved by incubating the grafts in antibiotic solution and freeze-drying again. Two biopolymers chitosan and alginate were used for creating sustained-release implantable coatings and the drug release profile was characterized in vitro by spectrophotometry. Using lyophilization with or without chitosan only resulted in short-term release that lasted up to 48 hours. Alginate coating enabled a sustained release that lasted for 8 days with amoxicillin, 28 days with ciprofloxacin coating, and 50 days with vancomycin coating. Using only implantable biodegradable allograft and polymers, a sustained release of antibiotics was achieved with ciprofloxacin and vancomycin for several weeks. Since the calculated daily release of the antibiotic was lower than the recommended IV dose, the calcium alginate coated bone graft can support endoprosthesis revision surgery.