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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.

Locally implantable antibiotic beads have been approved for their efficacy in treating chronic osteomyelitis. This study aimed to compare the in vitro elution characteristics of commercial antibiotic cement (Septopal^®) with those of custom-made gentamicin cement and gentamicin-loaded plaster of Paris. Septopal^® had a better inhibitive effect than custom-made gentamicin cement and gentamicin-loaded plaster of Paris for both S. aureus and P. aeruginosa at one month. The elution of gentamicin from Septopal^® declined gradually over one month in contrast to those of custom-made gentamicin cement and gentamicin-loaded plaster of Paris, which had a burst effect of elution and showed a small amount of gentamicin after one week. There was a significantly higher total amount of gentamicin eluted from Septopal^® than from other types of noncommercially prepared beads. The variability of the inhibitive effect of custom-made gentamicin cement was more pronounced than those of Septopal^® and gentamicin-loaded plaster of Paris groups. In conclusion, Septopal^® has a better elution characteristic than custom-made gentamicin cement and gentamicin-loaded plaster of Paris in the in vitro study.

Layered double hydroxide (LDH) is a layered hydroxide and exchangeable anion is intercalated in its interlayer. Application of the LDH as a controlled-release material of interlayer anions has become of interest, thus it is important to clarify the elution behavior of interlayer anions. We synthesized hydrogenphosphate-intercalated Mg/Fe and Zn/Fe LDH and elution of phosphate from these LDH were tested in deionized water, sodium chloride solution, sodium sulfate solution, and sodium carbonate solution. For Mg/Fe LDH, the amount of eluted phosphate increased with time and reached to maximum that increased as higher concentrate solution was used. The elution of phosphate from Mg/Fe LDH could be described by the pseudo second-order equation. This elution behavior was explained as ion-exchange reaction of phosphate with sulfate or carbonate in tested solution by means of kinetic simulation using Runge-Kutta method. In the eluted solution, metal ions contained in the LDH were detected and its amount depended on pH of the tested solution, that is, amounts of eluted Mg and Zn ions were small at higher pH (ca. 10) for Mg/Fe and Zn/Fe LDH respectively, but large amount of Zn ion was detected when 2.03 mol·l^-1 carbonate solution (pH = 13) was used. Thus elution of phosphate was caused by two main reactions: ion exchange and decomposition of the LDH.