The need for the localized delivery of antibiotics to infected wound sites remains a challenge for clinicians abroad. We asked whether chitosan could serve as a carrier for amikacin and daptomycin and if the eluted drugs were inhibitory to the growth of S. aureus.The turbidity assay only quantifies bacterial growth inhibition of an eluate. A bactericidal assay would likely reveal the ability of an eluted drug to eradicate bacteria in a contaminated wound site. We provided no calcium supplement to the agar that the daptomycin films were tested on. The lack of calcium could potentially alter the results; however, daptomycin inhibited S. aureus growth in this test without the added calcium. Finally, we had no literature against which to compare data in terms of amikacin and daptomycin release from chitosan films.We demonstrated the potential to incorporate commonly used antibiotics into a chitosan matrix. Like with other degradable delivery systems, there was considerable release of drug during the first few hours after testing [1, 2, 5, 7, 31, 37]. Amikacin recovery was much higher than that of daptomycin until the 72-hour timepoint. We found elution of antibiotic from chitosan much more rapid than reported for PMMA [3, 23, 27, 29]. PMMA is the gold standard in long-term antibiotic release from an implantable drug delivery system; however, the retrieval surgery necessary makes PMMA less than ideal. Our delivery system offers rapid release of drug in a biodegradable matrix. The elution of amikacin and daptomycin is similar to that in studies with loaded PLA drug delivery systems and systems that incorporate antibiotics into calcium sulfate. A study performed by Richelsoph et al. [31] showed higher than minimum inhibitory concentration (MIC) levels of tobramycin and daptomycin were released out to 28 days. The release of antibiotics in this study did not achieve the extended release rates seen with the Richelsoph study. The lack of extended release could be attributed to the binding nature of drug with chitosan or the initial loading amount. Further investigation should evaluate methods to extend elution time. Crosslinking the chitosan film might aid in extending release of the incorporated antibiotic. Studies have been performed using different crosslinking agents in combination with chitosan [17, 24, 36]. Genipin is a naturally occurring crosslinking agent that is several thousand times less cytotoxic than glutaraldehyde [36]. Evaluation of crosslinking antibiotic-loaded chitosan films are required to monitor changes in release rates of drug as well as determine the activity of eluted drugs.Drug activity of the eluates seemed unaffected by the weak acid solvent required to dissolve chitosan. Both drugs displayed excellent inhibition of bacterial growth at each timepoint. Previous studies demonstrate chitosan is bacteriostatic [8, 19, 25, 35, 38]; however, our study did not find plain chitosan bacteriostatic. The acidic solvent used could potentially be the reason for this discrepancy. The data acquired from the elution study in combination with the turbidity study results indicated a lower MIC of S. aureus when daptomycin is used. MIC ranges for both drugs can be found by expanding the turbidity study to include serial dilutions of known concentrations of each drug. Further testing of the eluates should include assays that can quantitatively measure the bactericidal activity of the eluted drug.These preliminary data offer insight to the possibility of delivering amikacin and daptomycin in a resorbable polymer, chitosan. Based on the biocompatible and biodegradable nature of chitosan as well as hemostatic and wound healing properties, it exhibits potential as an ideal localized carrier for antibiotics. The large variances in the concentration readings of daptomycin eluates should be investigated further. However, the inhibition of S. aureus growth by both amikacin-loaded films and daptomycin-loaded films is promising. Near complete inhibition of bacterial growth was seen with the eluates and films. Studies are ongoing to examine the effects of sterilization on both antibiotic release and activity. Additional studies are needed to further characterize the delivery system such as cytotoxicity tests, degradation tests, and in vivo evaluation. This study focused strictly on a 5% preload of antibiotic from 2% (w/v) chitosan films. Examination of different loading concentrations as well as different acidic solvents can possibly lead to a more optimal formulation for potential clinical therapy in treating musculoskeletal infections.
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