Figure 3a: FloSeal® (Baxter) hemostatic agent on a blood-agar plate incubated with Staphylococcus...
1
Figure 3a: FloSeal® (Baxter) hemostatic agent on a blood-agar plate incubated with Staphylococcus aureus . Floseal® mixed with microspheres (PLGA, 6- 23 μg): -without antibiotics ( placebo) placebo) or -with 440 μg gentamicin gentamicin (right). Significant growth inhibition was seen for up to 5-days afterwards. Placebo Gentamicin Figure 3b: Postoperative day 7; Spine sites with placebo and gentamicin microspheres side-by-side… Placebo Gentamicin Figure 1: Poly-L-Glycolic Acid microspheres after production. They measure 6-23 μm each. Introduction: Postoperative spinal wound infections occur at a rate of 1-5% in the non-compromised patient population undergoing elective posterior spinal surgery. Due to numerous systemic and local factors, this infection with primarily Staphylococcus aureus in the traumatized spine occurs at 6-12%. Returns to the operative room for irrigation and debridements added to the need for long term intravenous antibiotics lead to significant morbidity for the patient and pressures healthcare facilities with tremendous costs. Local hematoma harboring bacteria at the end of a procedure, combined with systemic malnutrition, tissue hypoxia and compromised skin under a brace or due to long-term supine positioning are important factors for this increased risk of infection. Postoperative spinal infection prevention Postoperative spinal infection prevention with gentamicin microspheres. with gentamicin microspheres. Kornelis A. Poelstra MD PhD *, Alexander R. Vaccaro MD # , Steven Lampro BS #, Christopher Adams PhD # ,Reid Rubsamen MD % , Todd J. Albert MD # * Department of Orthopaedics, University of Maryland – Shock Trauma, Baltimore MD # Rothman Institute, Thomas Jefferson University, Philadelphia, PA. % John Muir Medical Center, Walnut Creek, CA Methods: We developed a reliable, controlled release delivery system for gentamicin to wounds and hematoma using PLGA resorbable microspheres ( Figure 1 Figure 1 ). The spheres (6-25 micrometers, resorbtion in 3-10 days) were tested using a well published spinal infection model in 40 New Zealand White rabbits. After pharmacokinetics of the release were studied in-vitro and in-vivo, three non- contiguous sites (two treatment sites and one control site; Figure 2 Figure 2 ) were created in the spine of each rabbit, and wounds were challenged with S. aureus (ATCC 23593). After 7 days, postoperative wound infection was assessed using standard tissue sampling and bacterial quantification techniques (fascia, hematoma and bone) to test our hypothesis that both incidence as well as severity of postoperative spinal wound infection can be reduced using controlled, local delivery of gentamicin ( Figures 3a & 3b Figures 3a & 3b ) Results: Local delivery of PLGA gentamicin-microspheres resulted in controlled bactericidal levels of 20μg/ml hematoma for 72hrs, while powdered delivery of equal amounts of gentamicin resulted in cytotoxic ‘burst’-levels above 130μg/ml for the first 24hrs ( Figure 4 Figure 4 ). After 24hrs, powdered antibiotic levels tapered off rapidly to sub-therapeutic local concentrations, which could encourage antibiotic-resistance in remaining organisms. Systemic levels of gentamicin stayed < 0.2μg/ml in the serum. After establishing a reliable infection in 78% of all challenged control sites using 10 3 CFU S.aureus ( Figure 5 Figure 5 ), gentamicin-microsphere treatment reduced incidence of infection by 50% (p<0.01 – Chi-square; Figure 6 Figure 6 ). Also the severity of infection in the sites that did get infected was reduced in the treated sites compared to controls by 1.5 log values (p=0.03 – paired T-test Figure 7 Figure 7 ) for bacterial growth. All animals survived the procedure and no surgical complications occurred. Conclusion: Local delivery of antibiotics to wounds and hematomas in the spine is an intuitively attractive option to sterilize the local environment where intravenous antibiotic prophylaxis cannot reach (hypoxic, devitalized tissue and pooled hematoma lacking vascular flow). Powdered delivery, however, leads to cytotoxic levels of aminoglycosides (>100μg/ml) and is of only short duration. Gentamicin-microsphere controlled delivery successfully reduced the incidence and severity of S.aureus postoperative spinal wound infection while local bactericidal levels of gentamicin remained at 20μg/ml for a prolonged period of time. Minimal systemic penetration was detected, reducing side- effects and clearance. 0 20 40 60 80 100 120 140 160 0:00 2:00 4:00 10:00 23:59 Tim e postop (hrs) Figure 4: Postoperative pharmacokinetics for gentamicin inside the wound. = powdered gentamicin = microspheres (duplicate) 20μg/ml = bactericidal toxic level toxic level Figure 5: Establishing an ID-80 using a variety of concentrations. 10 3 CFU gave a reliable infection rate of ~80% without use of a spinal implant. 73 9 24 33 Total 100 0 9 9 10 5 100 0 7 7 10 4 78 2 7 9 10 3 25 3 1 4 10 2 0 4 0 4 10 1 Percentag e infected Not- infecte d Infecte d Total sites Inoculum (CFU S.aureus) 0.004 P-value: 8.25 Pearson Chi 2 0.001 P-value: 11.5 Likelihood ratio 50 50 11 11 22 Gent-Spheres 100 100 0 11 11 Control Percentage infected Not- infected Infect ed Total sites Treatment Figure 6: Gentamicin micro-spheres significantly reduced incidence of postoperative S.aureus wound infection in the spine by 50%. 1.0 6.88 Gent-Spheres 0.003 0.73 7.59 Control Paired T-test (P- value) St.Dev (log10 ) Average (log10) Treatment Figure 7: Gentamicin microspheres significantly reduced also severity of postoperative S.aureus wound infection in the spine in sites that did get infected despite the local microsphere treatment. TAKE HOME TAKE HOME INFECTION 1. Occurs at a high rate after posterior spine surgery; especially after trauma. 2. Patient factors typically cannot be changed 3. Local wound milieu is compromised: - dead-space defect fills with hematoma, often harboring bacteria, - hypoxia due to lengthy supine positioning postoperatively and bracing MANAGEMENT 1. Meticulous surgical technique. 2. Proper antibiotic prophylaxis and re-dosing during lengthy procedures. 3. Local application of microspheres for controlled release of antibiotics could become significant to sterilize the hematoma… 5. circumventing shelf-life complications with implant coatings Figure 2: New Zealand White rabbit infection model with three non- contiguous infection sites per animal. Two treatment sites and one control site can be created in a single animal, increasing significance of outcomes (via paired T-tests) and therewith reducing the number of animals needed for the study. Reference: Poelstra KA, Barekzi NA, Gristina AG, Grainger DW, Schuler TC. A novel spinal implant infection model in rabbits. Spine 2000;25;406-410
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Transcript of Figure 3a: FloSeal® (Baxter) hemostatic agent on a blood-agar plate incubated with Staphylococcus...
Figure 3a:FloSeal® (Baxter) hemostatic agent on a blood-agar plate incubated with Staphylococcus aureus. Floseal® mixed with microspheres (PLGA, 6-23 μg):
-without antibiotics (placebo)placebo)or -with 440 μg gentamicingentamicin (right).
Significant growth inhibition was seen for up to 5-days afterwards.
Placebo Gentamicin
Figure 3b:Postoperative day 7; Spine sites with placebo and gentamicin microspheres side-by-side…
Placebo Gentamicin
Figure 1:Poly-L-Glycolic Acid microspheres after production. They measure 6-23 μm each.
Introduction:
Postoperative spinal wound infections occur at a rate of 1-5% in the non-compromised patient population undergoing elective posterior spinal surgery. Due to numerous systemic and local factors, this infection with primarily Staphylococcus aureus in the traumatized spine occurs at 6-12%.
Returns to the operative room for irrigation and debridements added to the need for long term intravenous antibiotics lead to significant morbidity for the patient and pressures healthcare facilities with tremendous costs.
Local hematoma harboring bacteria at the end of a procedure, combined with systemic malnutrition, tissue hypoxia and compromised skin under a brace or due to long-term supine positioning are important factors for this increased risk of infection.
Postoperative spinal infection prevention with Postoperative spinal infection prevention with gentamicin microspheres.gentamicin microspheres.
Kornelis A. Poelstra MD PhD*, Alexander R. Vaccaro MD#, Steven Lampro BS#,
Christopher Adams PhD#,Reid Rubsamen MD%, Todd J. Albert MD#
* Department of Orthopaedics, University of Maryland – Shock Trauma, Baltimore MD
# Rothman Institute, Thomas Jefferson University, Philadelphia, PA. % John Muir Medical Center, Walnut Creek, CA
Methods:
We developed a reliable, controlled release delivery system for gentamicin to wounds and hematoma using PLGA resorbable microspheres (Figure 1Figure 1). The spheres (6-25 micrometers, resorbtion in 3-10 days) were tested using a well published spinal infection model in 40 New Zealand White rabbits.
After pharmacokinetics of the release were studied in-vitro and in-vivo, three non-contiguous sites (two treatment sites and one control site; Figure 2Figure 2) were created in the spine of each rabbit, and wounds were challenged with S. aureus (ATCC 23593).
After 7 days, postoperative wound infection was assessed using standard tissue sampling and bacterial quantification techniques (fascia, hematoma and bone) to test our hypothesis that both incidence as well as severity of postoperative spinal wound infection can be reduced using controlled, local delivery of gentamicin (Figures 3a Figures 3a & 3b& 3b) using PLGA microsphere technology.
Results:
Local delivery of PLGA gentamicin-microspheres resulted in controlled bactericidal levels of 20μg/ml hematoma for 72hrs, while powdered delivery of equal amounts of gentamicin resulted in cytotoxic ‘burst’-levels above 130μg/ml for the first 24hrs (Figure 4Figure 4).
After 24hrs, powdered antibiotic levels tapered off rapidly to sub-therapeutic local concentrations, which could encourage antibiotic-resistance in remaining organisms. Systemic levels of gentamicin stayed < 0.2μg/ml in the serum.
After establishing a reliable infection in 78% of all challenged control sites using 103 CFU S.aureus (Figure 5Figure 5), gentamicin-microsphere treatment reduced incidence of infection by 50% (p<0.01 – Chi-square; Figure 6Figure 6).
Also the severity of infection in the sites that did get infected was reduced in the treated sites compared to controls by 1.5log values (p=0.03 – paired T-test Figure 7Figure 7) for bacterial growth.
All animals survived the procedure and no surgical complications occurred.
Conclusion:
Local delivery of antibiotics to wounds and hematomas in the spine is an intuitively attractive option to sterilize the local environment where intravenous antibiotic prophylaxis cannot reach (hypoxic, devitalized tissue and pooled hematoma lacking vascular flow).
Powdered delivery, however, leads to cytotoxic levels of aminoglycosides (>100μg/ml) and is of only short duration. Gentamicin-microsphere controlled delivery successfully reduced the incidence and severity of S.aureus postoperative spinal wound infection while local bactericidal levels of gentamicin remained at 20μg/ml for a prolonged period of time. Minimal systemic penetration was detected, reducing side-effects and clearance.
0
20
40
60
80
100
120
140
160
0:00 2:00 4:00 10:00 23:59
Time postop (hrs)
ug/ml Gentamicin
Figure 4:Postoperative pharmacokinetics for gentamicin inside the wound.
= powdered gentamicin = microspheres (duplicate)
20μg/ml = bactericidal
toxic leveltoxic level
Figure 5:Establishing an ID-80 using a variety of concentrations. 103CFU gave a reliable infection rate of ~80% without use of a spinal implant.
7392433Total
100099105
100077104
78279103
25314102
0404101
Percentageinfected
Not-infected
InfectedTotal sitesInoculum(CFU S.aureus)
0.004P-value:8.25Pearson Chi2
0.001P-value:11.5Likelihood ratio
5050111122Gent-Spheres
10010001111Control
Percentageinfected
Not-infected
InfectedTotal sitesTreatment Figure 6:Gentamicin micro-spheres significantly reduced incidence of postoperative S.aureus wound infection in the spine by 50%.
1.06.88Gent-Spheres0.003
0.737.59Control
Paired T-test
(P-value)
St.Dev (log10)
Average (log10)
Treatment Figure 7:Gentamicin microspheres significantly reduced also severity of postoperative S.aureus wound infection in the spine in sites that did get infected despite the local microsphere treatment.
TAKE HOMETAKE HOMEINFECTION1. Occurs at a high rate after posterior spine surgery; especially after trauma.2. Patient factors typically cannot be changed3. Local wound milieu is compromised:
- dead-space defect fills with hematoma, often harboring bacteria,- hypoxia due to lengthy supine positioning postoperatively and bracing
MANAGEMENT1. Meticulous surgical technique.2. Proper antibiotic prophylaxis and re-dosing during lengthy procedures.3. Local application of microspheres for controlled release of antibiotics could become significant to sterilize the hematoma…5. circumventing shelf-life complications with implant coatings while distributing local prophylaxis over much greater wound-surface area to…6. Reduce bacterial adhesion and surface colonization of hardware.
Figure 2:New Zealand White rabbit infection model with three non-contiguous infection sites per animal.
Two treatment sites and one control site can be created in a single animal, increasing significance of outcomes (via paired T-tests) and therewith reducing the number of animals needed for the study.
Reference:Poelstra KA, Barekzi NA, Gristina AG, Grainger DW, Schuler TC. A novel spinal implant infection model in rabbits. Spine 2000;25;406-410
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