Can Antibiotic Beads Have An Impact In Osteomyelitis Cases?
Surgical debridement of infected bone is an unfortunate reality for those of us who frequently treat patients with diabetes. While adequate debridement is the most important step in treating osteomyelitis, many authors have commented on the adjunctive role of antibiotics in this clinical dilemma.1-3 Systemic antibiotics are routinely used preoperatively and have been advocated for six weeks or more. However, infected bone may become devascularized, making the delivery of systemic antibiotics less than desirable. Delivering systemic antibiotics may also be compromised when there is associated peripheral arterial disease in that extremity. The local insertion of antibiotic-impregnated materials has been commonly used to supplement surgical debridement of infected tissue and systemic antibiotics. Locally implanted antibiotics may provide reliably high concentrations of antibiotic to areas of infection while minimizing the potential systemic side effect from the use of high dose IV, IM or PO antibiotics.4Systemic levels of locally implanted antibiotics are rarely detectable (less than 1 percent) and there have been no reports of associated nephrotoxicity. The traditional vehicle of choice for locally introduced antibiotics has been polymethylmethacrylate (PMMA). One would combine PMMA with a heat stable antibiotic such as vancomycin or gentamycin and form it into beads. Then you would place the beads within the wound or bony cavity, forming a closed compartment either through primary closure or by using an occlusive film dressing to create a “bead pouch” for maintaining high levels of eluted antibiotic. Unfortunately, PMMA has several disadvantages including in vitro reports of local immune compromise and poor elution properties (less than 50 percent elution of antibiotic at four weeks).5-7 In addition, PMMA is not bioabsorbable so it must be surgically removed or left within the wound permanently. If one leaves the beads in, they may harbor bacteria in the future. However, if you remove them, overgrowth of granulation tissue and adherence to bone may make removal difficult and require a second surgical procedure. A Closer Look At Calcium Sulfate Beads For these reasons, biodegradable delivery systems for local antibiotic treatment are an attractive alternative to PMMA beads. At the University of Texas, we have begun using calcium sulfate beads impregnated with antibiotics to follow debridement and amputation procedures with primary closure in the diabetic foot wounds. We use the absorbable beads as an adjunct to surgical debridement and systemic antibiotics when we are treating patients who are recovering from osteomyelitis and extensive soft tissue infections. Calcium sulfate has been used as a bone graft substitute since the late 1800s. In 1997, medical grade calcium sulfate impregnated with tobramycin was introduced overseas. There have been positive reports of its use in combination treatment for osteomyelitis/surgical defects. Its favorable osteoconductive and elution properties have led to its use as an antibiotic delivery method for treating osteomyelitis and local soft tissue infection. Calcium sulfate is biodegradable and radiopaque with a predictable linear in vivo absorption and antibiotic elution rate.8-12 At one month, 33 percent of the calcium sulfate is absorbed and 91 percent and 100 percent are reabsorbed at three and six months respectively. Local elution of antibiotic is predictably linear over time with resulting high local concentrations.11 Systemic levels of tobramycin were undetectable following the first 24 hours. How To Create The Antibiotic Mixture Calcium sulfate is a commercially available product (OsteoSet, Wright Medical) but it is not FDA-approved to be sold with an impregnated antibiotic. Therefore, it is necessary to add the antibiotic of your choice to the calcium sulfate. One would mix the calcium sulfate, curing solution and antibiotic (vancomycin 500 mg or tobramycin/gentamicin 1 g) together and pour them into the pellet template that comes with the kit. Allow the pellets of 3 or 4 mm to harden in an exothermic reaction. After two minutes, they are ready to be implanted into the wound. Proceed to perform primary closure of the wound. Doing so facilitates a higher concentration of eluted antibiotic. You can see the antibiotic pellets on X-ray for up to three months.