Plasma and synovial fluid concentrations of linezolid in patients with knee osteoarthritis infected with Staphylococcus aureus

BACKGROUND: Linezolid is a new oxazolidinone antibiotic used for infections caused by methicillin-resistant Staphylococcus and other species. CASE PRESENTATION: Two cases of knee osteoarthritis with acute infection were successfully treated using linezolid. The plasma and synovial fluid concentrations of linezolid in two patients [women aged 69 and 73 years (cases 1 and 2)] with knee osteoarthritis infected with Staphylococcus aureus were measured after they were administered 600 mg twice daily by intravenous infusion. The plasma linezolid concentrations during knee surgery in case 1 at day 5 and in case 2 at day 2 were 19.6 and 15.6 μg/mL, respectively. The synovial fluid concentrations of linezolid in samples taken during surgery in case 1 and case 2 were 14.9 and 17.0 μg/mL, respectively; these values corresponded to ratios of synovial fluid/plasma of 76 and 109%. Possible metabolite 2-hydroxylated linezolid potentially mediated by cytochrome P450 2 J2 was not detected in the plasma or synovial fluid samples under the current clinical setting after multiple doses. CONCLUSIONS: These results implied nearly equivalent concentrations of linezolid in plasma and synovial fluid of clinical patients with knee osteoarthritis acutely infected with Staphylococcus aureus.