Antibiotic-leaching from polymethylmethacrylate beads.

Aminoglycoside-impregnated polymethylmethacrylate beads, which are used to deliver antibiotic directly to infected sites in the musculoskeletal system, are available as a manufactured product or they can be mold-made by a pharmacy or hand-rolled by the orthopaedist in the operating suite. We investigated the leaching of antibiotic from each of these types of beads. Our hypothesis was that the elutions of antibiotic from the three types of beads are similar. Three study groups (hand-made, mold-made, and manufactured beads), each composed of four five-bead subsets, were formed so that twenty beads of each type were tested. Each bead was leached daily in a two-milliliter aliquot of normal saline solution throughout a sixty-day period, and the aminoglycoside concentration in twenty of these aliquots was determined. Analysis of variance showed no statistically significant differences when the antibiotic elutions within each subset, between the different subsets, and between the three groups were compared. The clinically important finding of this investigation is that the leaching characteristics of the three types of aminoglycoside-impregnated beads are equivalent when the beads have been fabricated out of comparable materials.

Antibiotic-impregnated beads. Part II: Factors in antibiotic selection.

Part I of this series discussed the advantages of implanted antibiotic-impregnated polymethylmethacrylate beads over systemic therapy for managing chronic osteomyelitis and acute musculoskeletal infections. Numerous antibiotics are available for use in polymethylmethacrylate. However, specific characteristics should be considered prior to therapeutic selection: the antibiotic should be water-soluble, bactericidal, nontoxic to tissues, and readily available in powder form. In this concluding segment, the organisms most commonly cultured from orthopaedic infections and appropriate combinations of antibiotics and bone cements are outlined.

Antibiotic-impregnated beads. Part I: Bead implantation versus systemic therapy.

Parenteral antibiotic therapy for acute bone infections, soft-tissue infections, and osteomyelitis may result in high serum concentrations associated with nephrotoxic, ototoxic, and allergic complications. Conversely, the local release of antibiotics into the wound with the use of antibiotic-impregnated cement or antibiotic-impregnated polymethylmethacrylate beads has been found effective and does not induce negative effects or result in systemic concentrations of clinical significance. The antibiotic-impregnated cement beads are fabricated on a surgical steel wire, and they have bimodal elution properties. They provide local antibiotic concentrations that surpass the minimum inhibitory concentrations for pathogens commonly isolated in orthopaedic infections. Their use effectively controls chronic osteomyelitis and acute musculoskeletal infections. Compared with systemic antibiotic therapy, the incidence of nephrotoxic, ototoxic, and hypersensitivity reactions is significantly diminished. The beads release 5% of the antibiotic within the first 24 hours. The sustained elution then progressively diminishes to undetectable levels within a few weeks or months.