TOBRAMYCIN ELUTION FROM BONE SUBSTITUTE

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Abstract
Purpose: To determine the rate of antibiotic elution from tobramycin-impregnated ProOsteon (Interpore) and Collagraft (Zimmer). Methods: Five samples of Collagraft and ProOsteon were impregnated with a solution containing 1.2 g of tobramycin and 10 ml of sterile water. The samples were then allowed to dry overnight. These samples were stored at 37°C in separate test tubes containing phosphate buffered saline (PBS). The solution in each test tube was removed with a pipette at hours 3, 6, 9 and 12 and days 1, 2, 3, 5, 7, 9, 11 and 13. The PBS was then replaced. The pipetted solution was sent for laboratory quantification and also used in a bioassay to determine antibiotic level. To serve as a control, two additional samples of each bone graft that were not impregnated with antibiotic were placed in separate test tubes and subjected to the same protocol. Results: The antibiotic elution rate for both ProOsteon and Collagraft was high at 3 hours [5362 and 4875 μg/ml on day 3 (3.1 μg/ml) for the Collagraft and day 7 (3.7 μg/ml) for the ProOsteon]. Effective intravenous tobramycin level is considered to be 4–6 μg/ml. Conclusion: Bone graft substitute can be used as a delivery vehicle for tobramycin. In addition, antibiotic-impregnated synthetic bone graft may potentially fill a dead space or cavitary defect without the need for large autologous grafts and does not require later removal.