Staphylococcus aureus vertebral osteomyelitis: a single-centre retrospective cohort study with focus on oral flucloxacillin follow-up

International guidelines for Staphylococcus aureus vertebral osteomyelitis recommend 6 weeks of treatment, including oral follow-up using antibiotics with high bioavailability such as a fluoroquinolone/rifampicin combination. Oral flucloxacillin is not recommended due to low bioavailability and scarce evidence. However, flucloxacillin as oral follow-up treatment is common practice in Sweden based on favourable clinical experience, good tolerability, few interactions, and low ecological impact. Our aim was to review a single-centre experience of S. aureus vertebral osteomyelitis, with focus on flucloxacillin treatment.

A single-centre retrospective cohort of patients with Staphylococcus aureus vertebral osteomyelitis (n = 40) was identified between 2010 and 2016. Patients were further stratified by antibiotic treatment strategy with focus on oral flucloxacillin therapy (n = 24). Primary outcomes were relapse or death within 12 months of treatment initiation, and antibiotic-related adverse effects during treatment.

Methicillin-susceptible S. aureus (MSSA) caused 38 of the infections (95%), and five patients (13%) died, all in-hospital. Flucloxacillin was used for at least 75% of the oral treatment duration in 24 patients (60%). Median antibiotic treatment duration among these patients was 125.5 days (IQR 95-182), 109 days (IQR 76-149) of which comprised oral antibiotics. There were two relapses and two deaths among the patients treated predominantly with flucloxacillin, resulting in a composite clinical cure rate of 83% (20 of 24).

Prolonged oral flucloxacillin administration could be a potential treatment option for MSSA vertebral osteomyelitis. A prospective study of optimal treatment duration and dosing strategies for flucloxacillin in vertebral osteomyelitis is warranted.