Leslie A. Thomas DVM, Tatiana Bizikova MSc, Anne C. Minihan DVM, Diplomate ACVS Veterinary Surgery August 2011 40 6 774-780 Objective: To characterize the in vitro elution and bioactivity of 2 formulations of antibiotics in a novel, dissolvable, cross-linked dextran polymer matrix: Formulation 1—amikacin and clindamycin (AC); Formulation 2—amikacin, clindamycin, and vancomycin (ACV). Study Design: Prospective, in vitro, experimental study. Methods: Aliquots of the antibiotic impregnated polymer were incubated in PBS buffer for 10 days. PBS was changed every 24 hours and concentrations of the antibiotics eluted into saline were quantified. Antimicrobial activity of the eluent from each sampling period was tested for growth inhibition of Staphylococcus aureus. Results: Both formulations of R-gel™ had a rapid initial release of antibiotics within the first 24 hours and then the concentrations decreased gradually over 10 days. The concentration of amikacin, clindamycin, and vancomycin remained above the breakpoint minimum inhibitory concentration of each drug for a minimum of 9 days. No significant difference (P=.9938, P=.9843) was present in the elution pattern or total amount of antibiotic eluted from clindamycin or amikacin, respectively. Eluent from both groups demonstrated bioactivity against S. aureus for the entire 10-day study period. Conclusions: Amikacin and clindamycin together, or in combination with vancomycin, elute from R-gel™ effectively and at gradually decreasing concentrations for at least 10 days. The antibiotics maintained their bioactivity following polymerization and elution from the R-gel™.

• Antibiotic delivery
• Equine