Comparative evaluation of A-56619, A-56620, and nafcillin in the treatment of experimental Staphylococcus aureus osteomyelitis

A rabbit model for Staphylococcus aureus osteomyelitis was used to compare the results of treatment with A-56619 and A-56620, two new aryl-fluoroquinolones, and nafcillin. A-56619 (15 mg/kg) and A-56620 (20 mg/kg), both used for 28 days of treatment, were injected subcutaneously every 12 h, and nafcillin (40 mg/kg) was injected every 6 h. After treatment, S. aureus was found on bone marrow cultures from 19 of 20 control rabbits, 6 of 20 treated with A-56619, 14 of 20 treated with A-56620, and 8 of 20 treated with nafcillin. Drug concentrations in serum and uninfected and infected bone were measured 1 h after A-56619 and A-56620 injection and 30 min after nafcillin injection in a group of rabbits that had been infected for 3 to 4 weeks. The concentrations in infected bone were similar for all three drugs and were significantly higher than in uninfected bone. The results of this study showed that A-56619 had a high rate of eradication of S. aureus from infected bone and compared favorably to nafcillin.