Authors: Mclaren SG, Smeltzer MS, McLaren AC;
Title: Comparison of Xylitol and Glycine as fillers to increase the porosity of PMMA
Addresses: Depts of Orthopedics and Microbiology,
Univ of Arkansas for Medical Sciences, 4301 W Markham St. # 644, Little Rock AR
Purpose: To compare xylitol with glycine as a filler to increase the elution of daptomycin from Palacos polymethylmethacrylate (PMMA).
Methods: 7 mm beads were made in silicone molds using 1 gm daptomycin per batch of Palacos PMMA containing either 28 gm xylitol, 28 gm glycine or no filler. Groups of 5 beads were eluted in 20 ml buffered saline at 37oC. 5 ml of buffer was exchanged daily for 30 days. The eluant samples were assayed for antibacterial activity by serial dilution based on the ability to kill S. aureus strain UAMS-1, an osteomyelitis isolate previously shown to be sensitive to daptomycin at 1mcg/ml.
Results: Daptomycin concentration in the eluant from beads without filler was more than 30X the MBC on day1 and stayed above the MBC for 5 days. With glycine filler the initial concentration was more than 50X the MBC on day 1 and stayed above the MBC for 9 days. With xylitol filler the concentration was more than 80X the MBC on day 1 and stayed above the MBC for >10 days. Eluant from beads containing glycine or xylitol without daptomycin did not have an antibacterial effect on UAMS-1 even on day 1.
Discussion: This investigation confirms that biologically active daptomycin elutes from Palacos PMMA but that both the rate of elution and the total amount of antibiotic eluted over time increases dramatically with the addition of a filler. Xylitol was more effective than glycine in both regards. Together with the observation that xylitol has been reported to have anti-biofilm activity, this suggests that xylitol may be a more desirable agent than glycine to use as a filler. Confirmation of xylitol's ability to inhibit biofilm formation by UAMS-1 is ongoing work.
Significance: These data are valuable to help define the optimal antibiotic drug, dose, and filler combination to cost effectively deliver depot antibiotics to orthopedic materials related infections.