In vitro elution of gentamicin, amikacin, and ceftiofur from polymethylmethacrylate and hydroxyapatite cement

Objective-To compare the elution characteristics of ceftiofur and liquid an d powdered,gentamicin and amikacin from polymethylmethacrylate (PMMA) and f rom hydroxyapatite cement (HAC). Methods-PMMA and HAC beads in triplicate were impregnated with various amou nts and formulations of antibiotics. Beads were immersed in 5 mt of phospha te buffered saline that was replaced at 1, 3, 6, and 12 hours, and 1, 2, 3, 5, 7, 10, 14, 18, 22, 26, and 30 days. The eluent was stored at -70 degree s C until assayed within 2 weeks by microbiological assay (gentamicin and a mikacin) or capillary electrophoresis (ceftiofur). Results-Rate of elution for all beads was greatest within the first 24 hour s. Cumulative release of total antibiotic dose from beads over 30 days was significantly greater from HAC than PMMA. Antibiotic elution was directly r elated to the amount of antibiotic incorporated into the cement. Powdered a nd liquid forms of gentamicin had similar elution rates from PMMA. Elution of amikacin from PMMA beads was greater when the powdered form was used com pared with liquid amikacin. fluent concentrations of ceftiofur were similar to those of the aminoglycosides during the first 3 to 7 days but then decr eased precipitously by comparison. Conclusions-Elution of antibiotics from HAC was greater than from PMMA. Gen tamicin- and amikacin-impregnated PMMA and HAC released bactericidal concen trations of antibiotic for at least 30 days. Ceftiofur-impregnated PMMA or HAC is unlikely to provide long-term bactericidal concentrations. Clinical Relevance-Gentamicin and amikacin elute effectively from PMMA and HAC. (C) Copyright 2000 by The American College of Veterinary Surgeons.