In Vitro Elution of Tobramycin From Bioabsorbable Polycaprolactone Beads

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Abstract
To compare the in vitro elution characteristics of tobramycin impregnated beads made of polycaprolactone (PCL) and polymethylmethacrylate (PMMA). Six-millimeter PCL and PMMA beads with 6% tobramycin were formed and placed in phosphate-buffered saline or newborn calf serum and incubated at room temperature or 37°C. Aliquots were taken at intervals for eight weeks. Tobramycin levels were determined by fluorescent assay and antibacterial efficacy was assessed by measuring the zones of inhibition against Staphylococcus aureus and Pseudomonas aeruginosa on agar diffusion plates. Tobramycin elution rates at room temperature were similar up to three weeks. At three weeks, elution rates from PCL beads were twice those from PMMA beads, and at eight weeks, elution from PCL was quadruple that from PMMA. At 37°C, tobramycin elution rates from PCL were eight times greater than those from PMMA by eight weeks. Total tobramycin eluted from PCL beads was 38.9% and 20% in PMMA beads. All samples showed bacteriostatic activity against S. aureus and P. aeruginosa at eight weeks. These in vitro results show that PCL has superior antibiotic elution characteristics compared with PMMA, and this may translate into a more effective antibiotic delivery vehicle. In addition, PCL is a bioabsorbable polymer, which may decrease the need for a second surgical procedure to remove retained beads.