Background and Importance Cefiderocol is a new siderophore cephalosporin which effectively penetrates the outer cell membrane of gram-negative bacteria. Although several studies have demonstrated the efficacy of cefiderocol in the treatment of severe infections caused by multidrug-resistant gram-negative bacilli, current information on efficacy in osteoarticular infection is scarce.

Aim and Objectives We aimed to report a case of difficult-to-treat resistant Pseudomonas aeruginosa osteomyelitis successfully treated with cefiderocol for 6 weeks.

Material and Methods This is a 64-year-old diabetic male patient who developed a P. aeruginosa osteomyelitis secondary to a surgical wound infection following a supracondylar amputation. It was treated with multiple surgical debridement and several antibiotic series (ciprofloxacin, piperacillin/tazobactam and meropenem). Despite this, cultures from surgical site continued to grow P. aeruginosa which became multidrug-resistant, (only it was susceptible to colistin, aminoglycosides, ceftolozane/tazobactam and cefiderocol). Ceftolozane/tazobactam distribution was temporarily stopped at this time and amputation of the lower limb was believed to be the only option remaining.

The patient was treated with cefiderocol as a monotherapy for 6 weeks (June-August 2021) at a tertiary hospital, at a dose of 2 g every 8 hours administered in a 3-hour infusion. In addition, four surgical debridements were performed during this time.

Results After 3 weeks of therapy with cefiderocol, the wound swab cultures were negative. The patient remained afebrile during and at the end of the antibiotic therapy. No drug-related adverse effects or infusion reactions were reported. There was no leukopenia, leucocytosis, or worsening renal function. The inflammatory marker values decreased until they normalised and the magnetic resonance improved considerably after 6 weeks of treatment.

Two-control magnetic resonance and blood tests were performed, at week 15 and 45. They showed no evidence of persistent or recurrent infection and no elevations of acute phase reactants. Furthermore, the patient was febrile, asymptomatic and pain-free.

Conclusion and Relevance This case adds more experience to the scarce literature on the use of cefiderocol in P. aeruginosa osteomyelitis.

Its success in the treatment of osteomyelitis suggests that this drug penetrates well in bone tissue and could be a good therapeutic option, in conjunction with surgical debridement.

Conflict of Interest No conflict of interest