In vitro elution of tobramycin from bioabsorbable polycaprolactone beads

Objectives: To compare the in vitro elution characteristics of tobramycin i mpregnated beads made of polycaprolactone (PCL) and polymethylmethacrylate (PMMA). Design: Six-millimeter PCL and PMMA beads with 6% tobramycin were formed an d placed in phosphate-buffered saline or newborn calf serum and incubated a t room temperature or 37 degreesC. Aliquots were taken at intervals for eig ht weeks. Tobramycin levels were determined by fluorescent assay and antiba cterial efficacy was assessed by measuring the zones of inhibition against Staphylococcus aureus and Pseudomonas aeruginosa on agar diffusion plates. Results: Tobramycin elution rates at room temperature were similar up to th ree weeks. At three weeks, elution rates from PCL beads were twice those fr om PMMA beads, and at eight weeks, elution from PCL was quadruple that from PMMA. At 37 degreesC, tobramycin elution rates from PCL were eight times g reater than those from PMMA by eight weeks. Total tobramycin eluted from PC L beads was 38.9% and 20% in PMMA beads. All samples showed bacteriostatic activity against S. aureus and P. aeruginosa tit eight weeks. Conclusions: These in vitro results show that PCL has superior antibiotic e lution characteristics compared with PMMA, and this may translate into a mo re effective antibiotic delivery vehicle. In addition, PCL is a bioabsorbab le polymer, which may decrease the need for a second surgical procedure to remove retained beads.