Bone tissue concentrations of ciprofloxacin released from biodegradable screws implanted in rabbits skull

Previously, ciprofloxacin-releasing polylactide/polyglycolide 80/20 (SR-PLGA) screws have proven to be biocompatible with sufficient strength. However, there has been no information about the local concentrations of ciprofloxacin in bone tissue after their implantation. To measure bone concentrations of ciprofloxacin, two screws were implanted in each rabbit, one on either side of the sagittal suture (n = 28 rabbits). Follow-up periods were 2, 4, 8, 16, 24, 52 and 78 weeks. From each rabbit, bone blocks containing one screw were retrieved and used to measure drug concentration. Ciprofloxacin concentration at 2 weeks follow-up was 4.4 ± 4.2 μg/g, 14.1 ± 2.7 μg/g at 4 weeks and 7.6 ± 4.5 μg/g at 8 weeks. Measured concentrations were very low at 16 weeks (mean 0.09 ± 0.04 μg/g) and 24 weeks (mean 0.04 ± 0.02 μg/g). Surprisingly, the concentration was higher again at 1 year (mean 1.3 ± 1.0 μg/g). At 1.5 years, concentration had decreased again (mean 0.8 ± 0.6 μg/g). The drug concentration in bone tissue was higher than minimal inhibitory concentration of ciprofloxacin (Staphylococcus aureus 0.1–1.0 μg/g) at 2, 4, and 8 weeks. Ciprofloxacin-releasing SR-PLGA 80/20 screws could be used clinically for osteofixation and infection treatment in cranial bone.