2003 Abstract : S7 Nelson

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Authors: Nelson CL; McLaren AC; McLaren SG; DeClerk GR

Title: The Effect of Porosity on Elution of Gentamicin from Palacos PMMA Beads - A Pilot Study

Addresses: University of Arkansas for Medical Sciences, Little Rock, AR

Purpose: To measure the elution of gentamicin from Palacos TM polymethylmethacrylate (PMMA) as a function of inert filler load in combination with gentamicin dose.

Methods: Palacos PMMA was combined with crystalline glycine (0.450, 7, 14, or 28 gm) and with gentamicin powder (0.300, 1.2, 3.6, or 9.6 gm) per 40 gram batch. The powders were homogeneously mixed before adding the monomer. In the dough phase, the PMMA-gly-gent mixture was placed in 7 mm diameter silicone molds and allowed to harden. The beads were then placed in groups of 5 beads and weighed. The beads were placed in 20ml of phosphate buffered saline (PBS) and incubated at 37o C. Each day 5 ml of eluant was removed after mixing, and then replaced with 5ml of fresh PBS. 5ml eluant exchanges were carried out daily for 30 days. The removed eluant was labeled, frozen at -80o C, and stored until the time of assay. Assay of the 'Day 2' and 'Day 7' samples was carried out by fluorescence polarization immunoassay, using a TDx.

Results: Gentamicin concentration increased with increasing load of glycine and increasing dose of gentamicin. Gentamicin concentration in the eluant was > SeptopalR when the glycine content was 28 gm or greater, with the gentamicin dose 3.6gm or greater.

Discussion: The lowest dose combination of PMMA-gly-gent is similar to that associated with Septopal TM . Elution of Gentamycin from Septopal TM beads is greater than our measurements, suggesting that the proprietary manufacturing technology used to make Septopal TM beads is not reproduced by simple mixing, but, beads but the concentration of eluted gentamicin was much less. Results similar to the elution associated with Septopal TM beads were achieved by increasing the load of glycine and increasing the dose of gentamicin.

Significance: Elution seen with SeptopalR beads can be reproduced with hand mixed PMMA-gly-gent. Increasing the glycine load is significantly more cost effective than increasing the gentamicin dose.