Effectiveness of oral cephalexin in antibiotic-course completion for methicillin-susceptible Staphylococcus aureus-induced bacteremic vertebral osteomyelitis

Abstract Background Methicillin-susceptible Staphylococcus aureus (MSSA) is the most common causative microorganism of pyogenic vertebral osteomyelitis (PVO). Although oral antimicrobial therapy with first-generation cephalosporins can treat MSSA infection, data on PVO are scarce. This study evaluated the treatment efficacy of cephalexin as oral antibiotic therapy for MSSA-induced PVO. Methods This retrospective study included adult patients treated with oral cephalexin as the completing treatment for PVO with MSSA bacteremia from 2012 to 2020. Treatment effectiveness of cephalexin was evaluated by comparing improvement (5-point scale; score ≥ 4/5 indicates treatment success) in symptoms and laboratory and imaging results between intravenous antimicrobial and oral cephalexin treatment. Results Among 15 participants (8 [53%] women; median [interquartile range, IQR], age 75 [67.5–80.5] years; Charlson Comorbidity Index 2 [0–4]), 10 (67%) had lumbar spine lesions, 12 (80%) had spinal abscesses, and 4 (27%) had remote abscesses; no patients had concomitant endocarditis. In 11 patients with normal renal function, cephalexin 1,500–2,000 mg/day was administered. Five patients (33%) underwent surgery. Median (IQR; range) duration (days) of intravenous antibiotics, cephalexin, and total treatment was 36 (32–61; 21–86), 29 (19–82; 8–251), and 86 (59–125; 37–337), respectively. Cephalexin had an 87% treatment success rate without recurrence during a median follow-up of 119 (IQR, 48.5–350) days. Conclusions In patients with MSSA bacteremia and PVO, antibiotic treatment completion with cephalexin is a reasonable option, even in cases with spinal abscess, if at least 3 weeks of effective intravenous antimicrobial therapy is provided.