Evaluation of biodegradable ampicillin anhydrate microcapsules for local treatment of experimental staphylococcal osteomyelitis.

Successful treatment of chronic osteomyelitis requires sustained high concentrations of antibiotics locally within the infected bone. The efficacy of biodegradable (poly-DL-lactide-co-glycolide) microspheres containing 30.7% ampicillin anhydrate for the local treatment of experimental staphylococcal osteomyelitis was evaluated in rabbits. In the initial experiment, antibiotic therapy was initiated immediately following injection of Staphylococcus aureus into the proximal tibial metaphysis. A single intramedullary injection of microencapsulated ampicillin (100 mg) prevented osteomyelitis in all seven animals tested and was as effective as a two-week course of parenteral ampicillin administration. When antibiotic therapy was delayed for seven days, osteomyelitis developed in four of eight animals treated locally with microencapsulated ampicillin and in six of eight animals that received parenteral ampicillin therapy. When antibiotic therapy was delayed for seven days and was preceded by debridement, all ten animals treated locally with microencapsulated ampicillin had sterile bone cultures. In contrast, seven of ten animals treated locally with unencapsulated ampicillin powder developed osteomyelitis. Biodegradable antibiotic-loaded microspheres may be of clinical benefit for the local treatment of chronic osteomyelitis.