Oral step-down therapy is comparable to intravenous therapy for Staphylococcus aureus osteomyelitis

We hypothesized that regimens with an early switch to oral antibiotics are as effective as prolonged parenteral regimens for staphylococcal osteomyelitis.

We retrospectively reviewed records of adult patients with osteomyelitis caused by Staphylococcus aureus as determined by sterile site cultures, who had at least 6 months of follow-up post-therapy. The population was divided into two treatment groups: (1) an intravenous group (i.v.) that received > or = 4 weeks of parenteral therapy, and (2) a switch group that received < 4 weeks of intravenous followed by oral therapy.

A total of 72 patients (36 in each group) were identified with groups evenly matched for demographic and clinical characteristics. The overall apparent cure rate was 74%; 69% for the i.v. group and 78% for the switch group (P=0.59). Apparent cure rates were similar regardless of duration of intravenous therapy: 83% < 2 weeks, 72% 2-4 weeks, 75% 4-6 weeks and 66% > or = 6 weeks (P=0.68). Among the 39 patients who received rifampin-based combinations, those treated simultaneously with vancomycin and rifampin did significantly worse than those who received other rifampin combinations (P<0.02). Overall, MRSA infections responded poorly compared to MSSA (65% apparently cured versus 83%). However, 11/14 (79%) MRSA patients who received rifampin combinations, other than vancomycin and rifampin simultaneously, were apparently cured.

Overall outcomes did not differ significantly between i.v. and switch groups. Given the markedly lower costs and ease of administration, prolonged oral regimens after initial intravenous therapy may be a preferred regimen for staphylococcal osteomyelitis.