Biodegradable implants for potential use in bone infection. An in vitro study of antibiotic-loaded calcium sulphate.

Local antibiotic therapy by diffusion from plaster of Paris beads has proved promising in bone surgery. Sustained local delivery depends on thermostability, so we tested the antibacterial activity of 11 antibiotic solutions after storage at 37 degrees C using a microbiological method. Cephalosporins and penicillins were unstable, but aminoglycosides remained fully stable with 100% activity after 2 weeks. About 60% of the initial bactericidal activity of quinolone, glycopeptides and sodium fusidate were still detectable after 2 weeks. Release of these antibiotics from plaster of Paris beads was evaluated in vitro. Even those in the same family differed in their release rate. Plaster beads with sodium fusidate were the most effective association. A therapeutic level of glycopeptides, aminoglycosides and amoxicillin was leached for about 3 weeks. Cephalosporins and sodium amoxicillin were released in 2 to 3 days, and quinolone beads were too brittle to be used. Plaster of Paris, which is cheap, biocompatible and biodegradable, is an excellent carrier for sodium fusidate, aminoglycosides and glycopeptides.