What is the appropriate treatment duration for a 70-year-old diabetic nursing home patient with a chronic wound on the left big toe, now presenting with acute infection and suspected osteomyelitis, currently being treated with oral Metronidazole (Metronidazole) and intravenous Cefazolin (Cefazolin)?

From the Guidelines

For suspected osteomyelitis in a diabetic patient with a chronic toe wound that has improved but not resolved with initial antibiotic therapy, I recommend a 6-week course of antibiotics targeting Staphylococcus aureus, as suggested by the most recent guidelines 1. The preferred regimen would be intravenous cefazolin 2g every 8 hours, which can be transitioned to oral cephalexin 500mg four times daily after clinical improvement, based on the recommendation to use any of the systemic antibiotic regimens that have been shown to be effective in published randomised controlled trials at standard dosing 1. Alternatively, if MRSA is a concern, consider intravenous vancomycin with dosing based on therapeutic drug monitoring, potentially transitioning to oral linezolid 600mg twice daily. Metronidazole should be discontinued as it does not cover Staphylococcus aureus. Before starting this extended therapy, obtain an MRI to confirm osteomyelitis, as X-rays often miss early bone infection, as recommended by the guidelines 1. Blood tests including ESR, CRP, and repeat cultures would help monitor treatment response. Surgical debridement may be necessary if there is necrotic tissue or poor response to antibiotics. Regular wound care, glucose control, and offloading pressure from the affected toe are essential components of treatment. This extended antibiotic course is necessary because bone infections require prolonged therapy to fully eradicate the infection and prevent recurrence, as antibiotics penetrate bone tissue more slowly than soft tissue. Key considerations in managing this patient include:

• The use of conventional microbiology techniques for pathogen identification 1
• The importance of proper wound care and glucose control in promoting healing and preventing further complications
• The potential need for surgical intervention in cases of necrotic tissue or poor response to antibiotics
• The consideration of antibiotic stewardship principles in selecting and adjusting antibiotic therapy 1

From the FDA Drug Label

Adult diabetic patients with clinically documented complicated skin and skin structure infections ("diabetic foot infections") were enrolled in a randomized (2:1 ratio), multi-center, open-label trial comparing study medications administered IV or orally for a total of 14 to 28 days of treatment The cure rates by pathogen for microbiologically evaluable patients are presented in Table 19. Table 19 Cure Rates at the Test-of-Cure Visit for Microbiologically Evaluable Adult Patients with Diabetic Foot Infections Pathogen Cured ZYVOX n/N (%) Comparator n/N (%) Staphylococcus aureus 49/63 (78) 20/29 (69) Methicillin-resistant S aureus 12/17 (71) 2/3 (67)

The patient has a diabetic foot infection with Staphylococcus aureus. The treatment with linezolid for 14 to 28 days is a possible option.

• The cure rate for Staphylococcus aureus is 78%.
• The cure rate for Methicillin-resistant S aureus is 71%. The treatment duration should be 14 to 28 days 2.

From the Research

Treatment of Osteomyelitis

• The patient is currently being treated with oral metronidazole and intravenous cefazolin for a suspected osteomyelitis infection, with the infection showing some improvement 3, 4.
• However, osteomyelitis is often a surgical disease, and a multidisciplinary approach to treatment is often required, including medical and surgical therapy 3.
• The duration of antibiotic therapy may be shortened considerably after surgical intervention, but in cases where surgery is not an option, long-term antibiotics may be used as suppressive therapy along with adjunctive local treatments 3.

Antibiotic Treatment

• Staphylococcus aureus is the most common pathogen cultured from bone samples in diabetic foot osteomyelitis, and the antibiotic of choice for treatment of osteomyelitis caused by methicillin-resistant staphylococci (MRS) is vancomycin, although other alternatives such as daptomycin or teicoplanin are also considered 5, 6.
• Ceftriaxone and cefazolin have been shown to be effective in the treatment of osteomyelitis, although ceftriaxone is less active than standard antistaphylococcal agents 7, 4.
• The combination of ceftaroline and daptomycin has been studied as an alternative treatment for complicated osteomyelitis, including methicillin-resistant S. aureus (MRSA) and methicillin-resistant S. epidermidis (MRSE) 6.

Treatment Duration

• Studies have shown that a protocol of 6 weeks of intravenous antibiotics may be appropriate to treat osteomyelitis, although this is controversial and often not curative 3.
• The duration of antibiotic therapy may need to be individualized based on the patient's response to treatment and the presence of any underlying medical conditions, such as diabetes or peripheral vascular disease 3, 5.