Vancomycin–Gentamicin Calcium Sulfate Beads May Predispose to Polymicrobial Infections After Adult Spinal Deformity Surgery
Key findings
- This retrospective study investigated the use of intrawound vancomycin–gentamicin calcium sulfate beads for gram-positive and gram-negative coverage during adult spinal deformity surgery
- Surgical site infection rates did not differ significantly between 58 patients receiving combination therapy (5.2%), 66 who received vancomycin-impregnated calcium sulfate beads (1.5%), and 36 historical controls who received vancomycin powder (11.1%)
- All infections in the combination therapy group were polymicrobial, including some with virulent pathogens, whereas pathogens in the historical control group varied among gram-positive and gram-negative monomicrobial infections
- Further study of vancomycin–gentamicin calcium sulfate beads is needed before widespread routine use can be recommended for surgical prophylaxis
The efficacy of intrawound vancomycin powder as prophylaxis against surgical site infection in adult spine surgery is uncertain, which has prompted interest in alternatives. One potential option is vancomycin-laden calcium sulfate beads, but they have not demonstrated success in preventing gram-negative infection.
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Researchers at Massachusetts General Hospital have been testing vancomycin–gentamicin impregnated calcium sulfate beads, but they recently provided preliminary evidence that this combination therapy may predispose patients to polymicrobial infections.
Grace X. Xiong, MD, formerly part of the Harvard Combined Orthopaedic Residency Program, Stuart H. Hershman, MD, chief of the Orthopaedic Spine Service at Mass General, and colleagues report in The Spine Journal.
Methods
The team retrospectively studied 161 adults who underwent thoracolumbar instrumented fusion at Mass General for spinal deformity:
- 66 were treated between October 2018 and March 2021 and received molded beads formed from 1 gram vancomycin and 10 cc calcium sulfate, placed subfascially before closure (vancomycin bead group, VB)
- 58 were treated between April 2021 and January 2022 and received beads formed from 1 gram vancomycin mixed with 120 mg gentamicin and 10 cc calcium sulfate (vancomycin/gentamicin bead group, VGB)
- 36 historical controls received 1 gram of intrawound vancomycin powder (vancomycin powder group, VP)
All patients received standard institutional perioperative antibiotic prophylaxis and layered wound closure over a deep drain.
Results
The surgical site infection rate was 1.5% in the VB group, 5.2% with VGB, and 11.1% with VP. None of the differences were statistically significant, including after adjustment for age and estimated blood loss. Details of the infections were:
- VB group—One patient with intra-abdominal bowel perforation developed a Klebsiella pneumoniae gram-negative infection
- VGB group—All infections were polymicrobial, ranging from opportunistic pathogens that stem from commensal skin flora (e.g., Cutibacterium acnes, Staphylococcal epidermidis) to more virulent or non-commensal pathogens (e.g., Pseudomonas aeruginosa, Enterobacter cloacae)
- VP group—One gram-positive monomicrobial infection (S. epidermidis), two gram-negative monomicrobial infections (K. pneumoniae, P. aeruginosa), and one Escherichia coli infection as part of a polymicrobial burden; hematogenous spread from urinary sources did not appear to contribute substantially to infection in this group
The groups did not differ significantly in rates of aseptic wound drainage (4% overall) or acute kidney injury (8.8%).
Ramifications for Antibiotic Prescribing
This analysis was designed to explore the feasibility and safety of combination vancomycin/gentamicin therapy rather than conclusive differences in infection rates. Still, the results may have implications for individualized long-term antibiotic therapy and stewardship on a community and global level.
The study findings don't preclude the targeted use of vancomycin/gentamicin therapy in specific applications with sensitive pathogens in known infections. However, before combination therapy can be recommended for routine surgical prophylaxis, larger multicenter studies are needed that explore efficacy, the potential for nephrotoxicity, and optimal dosing.
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