Elution of Clindamycin and Enrofloxacin From Calcium Sulfate Hemihydrate Beads In Vitro

Objective: To compare the in vitro elution characteristics of clindamycin and enrofloxacin from calcium sulfate hemihydrate beads containing a single antibiotic, both antibiotics, and each antibiotic incubated in the same eluent well. Study Design: Experimental in vitro study. Methods: Calcium sulfate hemihydrate beads were formed by mixing with clindamycin and/or enrofloxacin to create 4 study groups: (1) 160mg clindamycin/10 beads; (2) 160mg enrofloxacin/10 beads; (3) 160mg clindamycin+160mg enrofloxacin/10 beads; and (4) 160mg clindamycin/5 beads and 160mg enrofloxacin/5 beads. Chains of beads were formed in triplicate and placed in 5mL phosphate buffered saline (PBS; pH 7.4 and room temperature) with constant agitation. Antibiotic-conditioned PBS was sampled at 14 time points from 1 hour to 30 days. Clindamycin and enrofloxacin concentrations in PBS were determined using high-performance liquid chromatography. Results: Eluent concentrations from clindamycin-impregnated beads failed to remain sufficiently above minimum inhibitory concentration (MIC) for common infecting bacteria over the study period. Enrofloxacin eluent concentrations remained sufficiently above MIC for common wound pathogens of dogs and cats and demonstrated an atypical biphasic release pattern. No significant differences in elution occurred as a result of copolymerization of the antibiotics into a single bead or from individual beads co-eluting in the same eluent well. Conclusion: Clindamycin-impregnated beads cannot be recommended for treatment of infection at the studied doses; however, use of enrofloxacin-impregnated beads may be justified when susceptible bacteria are cultured.