Local antibiotic delivery by a bioabsorbable gel is superior to PMMA bead depot in reducing infection in an open fracture model.
OBJECTIVE
Local delivery allows a high concentration of antibiotics to be achieved in the wound while avoiding the side effects and cost of systemic administration. Beads molded from polymethylmethacrylate cement are commonly used for local antibiotic delivery but are not ideal. The purpose of this study was to determine whether a bioabsorbable gel delivering vancomycin and gentamicin is more effective in reducing infection than beads delivering vancomycin and tobramycin.


METHODS
This study used a segmental defect rat model contaminated with Staphylococcus aureus and treated with clinically relevant local antibiotic doses, delivered by gel or beads. In the gel group, 1 mL of gel containing gentamicin and vancomycin was spread throughout the wound. In the bead group, four 3-mm beads containing tobramycin and vancomycin were placed in the wound, 2 in the defect and 2 in the adjacent tissue envelope, there was also a control group that received no antibiotic treatment. After 14 days, bone and hardware was harvested for separate microbiological analysis.


RESULTS
There was a significantly lower infection rate in groups treated with antibiotics delivered by gel compared with those treated with either antibiotic beads or no antibiotics at all (P < 0.001). Quantitative cultures also demonstrate significantly less bacteria in the wounds treated with the gel than in the control or bead groups (P ≤ 0.004).


CONCLUSIONS
These results suggest that antibiotic delivery by a gel is superior to beads. The authors propose that antibiotic depot by polymethylmethacrylate antibiotic beads is less effective because this method has to rely on diffusion of the antibiotic from the high concentration close to the beads to all regions of the wound.
*Extremity Trauma and Regenerative Medicine, US Army Institute of Surgical Research, San Antonio, TX; †Academic Department of Military Surgery and Trauma, Royal Centre for Defence Medicine, Birmingham, United Kingdom; and ‡Infectious Disease Service, Brooke Army Medical Center, San Antonio, TX.
Jowan G
JG
Penn-Barwell
Clinton K
CK
Murray
Joseph C
JC
Wenke
D020341:Absorbable Implants; D000287:Administration, Topical; D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage*; D004195:Disease Models, Animal; D004337:Drug Carriers / Q000008:administration & dosage; D005264:Femoral Fractures / Q000150:complications* / Q000601:surgery; D005597:Fractures, Open / Q000150:complications* / Q000601:surgery; D005782:Gels; D005839:Gentamicins / Q000008:administration & dosage; D019904:Polymethyl Methacrylate; D051381:Rats; D013203:Staphylococcal Infections; D013211:Staphylococcus aureus; D013530:Surgical Wound Infection / Q000209:etiology / Q000382:microbiology / Q000517:prevention & control*; D014031:Tobramycin / Q000008:administration & dosage; D014640:Vancomycin / Q000008:administration & dosage
D000900:Anti-Bacterial Agents; D004337:Drug Carriers; D005782:Gels; D005839:Gentamicins; D014640:Vancomycin; D019904:Polymethyl Methacrylate; D014031:Tobramycin