| Summary: | 碩士 === 長庚大學 === 醫療機電工程研究所 === 105 === Background: Antibiotic-load bone cement (ALBC) has been widely used in the prophylaxis and treatment of orthopedic infections. Prophylaxis requires low doses of antibiotics in bone cement to reduce the risk of infection. In the treatment of musculoskeletal infections, ALBC by means of beads or spacers is impregnated with higher doses for guarantee of healing from infection. Numerous reports had demonstrated that in vitro antibiotic elution from acrylic cement is proportional to the surface area of exposed cement in a liquid medium. It is also well known that the amount of antibiotic impregnated in cement is an important factor to influence the elution efficacy. To our knowledge, no reports have compared the elution characteristics of ALBCs with a combination of identical surface area but varying volume in an in vitro model. The aim of this study is to compare the release of vancomycin as a function of time and to relate the antibiotic release with varying surface area-to-volume ratio on condition of high or low dosage of vancomycin.
Methods: Two dosages of vancomycin in 40g bone cement were used to represent the high (4g vancomycin) and low (1g vancomycin) dose groups. Six groups of spherical shape of ALBCs with an identical outer diameter of 35 mm were made using a home-made rubber mold. One group of ALBCs contains full mixture of antibiotic and cement (control). For the remaining 5 groups, metal spheres with different diameters were embedded at the center of the spherical ALBCs for each designated group. These lead to the ALBS specimens with identical surface area but varying thickness (1, 1.5, 3, 5 and 10 mm, respectively). Three specimens in each group were then used to measure antibiotic elution. Each specimen was immersed in a glass tube containing 50 ml of sterile phosphate buffer solution and kept at 37 °C until the designated sampling times. Accumulation release of vancomycin from ALBC was measured for up to 168 hours.
Results: 1). A higher release rate of vancomycin was found at the initial stage. The release rate decreases with increasing elution period. 2). Regardless of vancomycin dosage (high or low), there was no significant difference in accumulated amount of release vancomycin among groups. 3). Regardless of vancomycin dosage, a thinner specimen (higher ratio of surface area to volume) presents higher release efficiency (amount of released antibiotics divided by total amount of antibiotics in cement). 4). For specimen with identical thickness (volume), Specimen with high vancomycin dosage (high concentration) presents higher release efficiency as compared to that of specimen with low vancomycin dosage.
Conclusion: Both surface area and concentration play important role in antibiotics elution. On circumstance of identical surface area and identical concentration, the volume (total amount of antibiotics) of ALBC does not significantly alter the accumulated release amount of vancomycin.
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