The suitability of biodegradable poly(dl-lactide-co-glycolide)75:25 microspheres for the sustained release of antibiotics

Post-operative infections resulting from total hip arthroplasty are caused by bacteria such as Staphylococcus aureus and Pseudomonas aeruginosa entering the wound perioperatively or by haemetogenous spread from distant loci of infection. They can endanger patient health and require expensive surgical revision procedures. Gentamicin impregnated poly (methyl methacrylate) bone cement is traditionally used for treatment but is often removed due to harbouring bacterial growth, while bacterial resistance to gentamicin is increasing. The aim of this work was to encapsulate the antibiotics vancomycin, ciprofloxacin and rifampicin within sustained release microspheres composed of the biodegradable polymer poly (dl-lactide-co-glycolide) [PLCG] 75:25. Topical administration to the wound in hydroxypropylmethylcellulose gel should achieve high local antibiotic concentrations while the two week in vivo half life of PLCG 75:25 removes the need for expensive surgical retrieval operations. Unloaded and 20% w/w antibiotic loaded PLCG 75:25 microspheres were fabricated using a Water in Oil emulsification with solvent evaporation technique. Microspheres were spherical in shape with a honeycomb-like internal matrix and showed reproducible physical properties. The kinetics of in vitro antibiotic release into newborn calf serum (NCS) and Hank's balanced salt solution (HBSS) at 37°C were measured using a radial diffusion assay. Generally, the day to day concentration of each antibiotic released into NCS over a 30 day period was in excess of that required to kill St. aureus and Ps. auruginosa. Only limited microsphere biodegradation had occurred after 30 days of in vitro incubation in NCS and HBSS at 37°C. The moderate in vitro cytotoxicity of 20% w/w antibiotic loaded microspheres to cultured 3T3-L1 cells was antibiotic induced. In conclusion, generated data indicate the potential for 20% w/w antibiotic loaded microspheres to improve the present treatment regimens for infections occurring after total hip arthroplasty such that future work should focus on gaining industrial collaboration for commercial exploitation.