Introduction

Clindamycin and enrofloxacin are often utilized for the systemic treatment of infection. Local therapy is a useful alternative to systemic administration of antibiotics as high concentrations can be obtained at surgical sites with little risk of systemic toxicity.

Objectives

To compare the in vitro elution of clindamycin and enrofloxacin from calcium sulfate hemihydrate beads of one antibiotic, beads of both antibiotics, and beads of each antibiotic placed in the same eluent well.

Methods

Four study groups were created:

 160 mg clindamycin/10 beads

 160 mg enrofloxacin/10 beads

 160 mg clindamycin and 160 mg enrofloxacin/10 beads

 320 mg clindamycin/5 beads and 320 mg enrofloxacin/5 beads

Beads were placed in 5 mL phosphate-buffered saline (PBS) at pH 7.4 and room temperature with constant agitation. PBS was sampled at time points from 1 hour to 30 days. Antibiotic concentrations were determined using high-performance liquid chromatography (HPLC).

Results

Elution of clindamycin was not effective; eluent concentrations were not maintained sufficiently above the MIC for common infecting bacteria over the study period. Enrofloxacin elution was effective. Enrofloxacin demonstrated a novel biphasic elution pattern not commonly observed of eluting antibiotics. 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.

Conclusions

Clindamycin-impregnated beads cannot be recommended for long-term treatment of infection at the studied doses. Clindamycin beads may offer prophylaxis against infection. Use of enrofloxacin-impregnated beads is justified when susceptible bacteria are cultured.