Once daily high-dose gentamicin to prevent infection in open fractures of the tibia shaft: A preliminary investigation. (*).
Background. Cephalosporin and aminoglycoside antibiotics are currently recommended for infection prophylaxis in high-energy open tibial shaft fractures. We evaluated cephalosporin in conjunction with once daily high-dose gentamicin as prophylaxis against infection in Gustilo types II and III open tibial shaft fractures.
Methods. Sixteen patients were identified in whom once daily gentamicin dosing was used as part of an antibiotic prophylaxis regimen in patients with types II and III open tibial shaft fractures. Cefazolin (1 g) and gentamicin (5 mg/kg) were given before operation. Antibiotic therapy was continued for 48 hours after definitive wound closure. Monitoring for gentamicin toxicity consisted of blood urea nitrogen (BUN) and creatinine levels, gentamicin trough levels, and a daily query for signs of prodromal ototoxicity.
Results. Average time to fracture union was 8 months. One superficial and two deep infections were observed. No patient showed signs of nephrotoxicity or ototoxicity.
Conclusions. Our investigation suggests that this dosing regimen might be safe as prophylaxis against infection in open tibial shaft fractures and that it warrants further study.
THE TIBIA is the most commonly fractured long bone, and many of these fractures are open. (1) The incidence of infection is noted to be 10 to 20 times higher in open tibial fractures than other open fractures. (2) Open tibial fractures are susceptible to infection due to several factors, including the high energy imparted to the leg, the poor blood supply of the tibia, and contamination of the fracture site at injury. (3) Several studies have shown that antibiotics significantly decrease the infection rate associated with open tibial shaft fractures. (2,4-6) It is generally agreed that a cephalosporin should be given in all open tibial shaft fractures. The addition of an aminoglycoside has been advocated for Gustilo types II and III open fractures (4,7) because of the higher incidence of gram-negative organisms contaminating these more severe open fractures. (2,4,8) Gentamicin is an aminoglycoside commonly used in prophylaxis against gram-negative colonization of open tibial fractures; however, institutional differences exist regarding the dose and dosing interval. A recent study has shown good results using a large daily dose of gentamicin in open fracture prophylaxis. (9) The purpose of this review was to investigate the efficacy of a 5 mg/kg daily dose of gentamicin in conjunction with a cephalosporin to prevent infection in operatively stabilized Gustilo types II and III open tibial shaft fractures.
MATERIALS AND METHODS
Between May 1, 1995, and May 31, 1999, 52 patients between the ages of 18 and 65 with an operatively treated Gustilo type II or III open tibial shaft fracture were identified using a prospectively gathered trauma registry. Three patients who had primary amputation and 2 who had delayed amputation were excluded from the study. Fifteen patients who received cefazolin only, 4 who received broad spectrum antibiotics, 2 who received twice daily gentamicin, and 2 others with incomplete antibiotic records were also excluded from the study. The remaining 24 patients received a cephalosporin and a once daily gentamicin dose of 5 mg/kg. Of these 24 patients, four were lost to follow-up, and four had follow-up for less than 3 months and were excluded from the study, leaving 16 patients for review (Table). There were 3 type II, 6 type IIIA, 5 type IIIB, and 2 type IIIC open fractures. There were 15 men and 1 woman, with an average age of 35 years (range, 28 to 65 years). The average Injury Severity Score (10 was 16 (rang e, 9 to 34). Fractures resulted from crushing injury in 2 patients, gunshot wound in 2, motorcycle accident in 3, pedestrian-car accident in 6, and motor vehicle accident in 3. Follow-up averaged 15 months (range, 3 to 42 months).
Patients were initially assessed and stabilized in the emergency room by the trauma surgery service, which then consulted orthopaedic surgery. A Betadine dampened sponge was placed over the open wound, and the lower extremity was splinted to minimize soft tissue damage. Attempts were made to obtain radiographs before splint application. Intravenous cefazolin (1 g) was administered on arrival to the emergency room. Gentamicin (5 mg/kg) was given if the patient had normal BUN and creatine levels, no history of either renal disease or granulocytopenia, and was not pregnant. After clearance by the trauma surgery service, patients were taken to the operating room for irrigation, debridement, and fracture stabilization.
Wound debridement was done in a meticulous fashion. The open wound was extended proximally and distally approximately 5 cm to facilitate visualization and wound debridement. After initial debridement, the wound was irrigated with 9,000 mL of pulsed lavage (Stryker, Kalamazoo, Mich). Inspection of the open wound was repeated after the irrigation, and debridement was continued as indicated by wound contamination. At completion of debridement, fractures were stabilized using a 4.5 mm plate, 2 reamed nails, 4 external fixators, and 9 unreamed nails. All but one patient, who had a primary wound closure, were returned to the operating room every 48 hours for repeat irrigation and debridement until the wound was clean, at which time the wound was closed. Additional wound closure techniques consisted of 9 delayed primary closures, 4 rotational tissue transfers, and 2 free tissue transfers. Intravenous administration of antibiotics was continued for 48 hours after the definitive wound closure, except in rotational an d free tissue transfers, for which antibiotics were continued until drains were removed.
Monitoring for gentamicin serum levels consisted of gentamicin trough determination 30 minutes before the third dose. For patients with an elevated gentamicin trough level, the dosage was decreased, and the trough measurement was repeated before the subsequent third dose. Gentamicin-associated nephrotoxicity was assessed by serologic monitoring of renal function consisting of BUN and creatinine levels examined every 2 days. Each patient who was responsive was queried about prodromal signs of ototoxicity (hearing loss, tinnitus, and dizziness). Audiograms were not obtained.
After discharge from the hospital, patients were examined 2 weeks postoperatively and every 4 to 6 weeks thereafter until fracture union. Further follow-up was arranged on an independent basis. Signs and symptoms of infection were carefully sought. Superficial infections were defined as infections superficial to bone not requiring surgical intervention. (3) Deep infections were defined as those that communicated with the site of the fracture, necessitating operative irrigation and debridement. (3) Serologic examinations of renal function were not done. Audiograms were not done, but patients were asked about possible prodromal signs of ototoxicity during return clinic examinations.
Fracture union was achieved in all patients an average of 8 months from the index procedure (range, 3 to 28 months). Seven patients required 9 subsequent procedures to obtain bony union, including 1 external fixator adjustment, 3 iliac crest bone grafting procedures, 2 nail dynamizations (removal of locking screws from the nail on one side of the fracture, thereby allowing francture compression), and 3 nail exchanges. Seven other procedures in 3 patients were required for soft tissue management or to control infections after initial wound closure. One patient who had a free tissue muscle transfer required an operative debridement for removal of the flap after it necrosed. The wound ultimately healed with dressing changes. Our 2 patients who had deep infections required 6 subsequent debridements and a nail removal to control the infections. No patient had either nephrotoxicity or ototoxicity (Table).
One patient treated with external fixator had a superficial pin tract infection. This infection was treated on an outpatient basis with oral antibiotics and vigilant pin care. Two patients had deep infections. One of these patients (No. 5, Table) sustained a type IIIA open fracture from multiple low-velocity gunshot wounds (Fig 1). This fracture was stabilized on the night of admission with a reamed intramedullary nail after irrigation and debridement (Fig 2). After 48 hours, irrigation and debridement were repeated, accompanied by delayed primary wound closure. Four months postoperatively, after one previous follow-up examination, fluctuation occurred at the most proximal gunshot wound. Local irrigation and debridement were done, and the patient was given oral antibiotics for a Staphylococcus aureus infection. At 6 months postoperatively, the patient returned with drainage from the abscess location with evidence of a nonunion. A reamed exchange nailing was done, and the patient was treated with intravenous cefazolin and oral ofloxacin for combined S aureus and Serratia marcescens infections. Three months after the exchange nail, the patient returned with a questionable fracture union and drainage from the proximal locking screw wounds, for which local irrigation and debridement were done in the office. Four months after exchange nailing, drainage occurred from the proximal locking screw sites. The patient had nail removal with reaming of the intramedullary canal and was again given oral ofloxacin. The patient was last seen in our hospital for an unrelated admission 17 months after injury. At that time, the patient's leg was healed, without evidence of further infection (Fig 3).
The other patient with a deep infection (No. 1, Table) sustained a type IIIC open fracture resulting from a crush injury. The patient was treated with immediate revascularization, irrigation and debridement, and bony stabilization with an external fixator. The patient required four additional debridements before a local gastrocnemius muscle transfer. Six weeks after wound closure, a deep infection due to S marcescens and Staphylococcus epidermidis developed. The patient required four subsequent debridements and a modification of antibiotic therapy to intravenous ceftriaxone and vancomycin to eradicate the infection. The fracture healed 12 months after injury.
Infection after open tibial shaft fractures has been reported in up to 50% of patients. (3-5,8,11) On the basis of several studies showing high levels of staphylococcal species as well as gram-negative species, treatment of high-energy open fractures has evolved to include cephalosporin and aminoglycoside antimicrobial prophylaxis. (6,8) Most institutions use 1 or 2 g of cefazolin as prophylaxis against gram-positive organisms; however, many institutional differences exist regarding the type, the dose, and dosing interval of aminoglycosides. (3,6,8,11)
Unlike [beta]-lactam antibiotics, aminoglycoside antibiotics have concentration-dependent bactericidal activity. As the ratio of peak concentration to minimum inhibitory concentration increases, bactericidal activity of aminoglycosides increases. (12,13) Aminoglycosides also show persistent suppression of bacterial growth after antimicrobial exposure, commonly termed the postantibiotic effect. The precise mechanism is unknown; however, it has been postulated that aminoglycosides bind irreversibly to bacterial ribosomal subunits, inducing damage to bacteria. (13,14) Furthermore, evidence suggests that the postantibiotic effect is potentiated by increased antibiotic concentrations up to 10 times the minimum inhibitory concentration. (14,15)
Elevated serum trough levels are responsible for the nephrotoxic effects of aminoglycosides. Nephrotoxicity, the most common adverse effect seen with aminoglycoside usage, results from accumulation of drug in the renal cortex, causing proximal tubular necrosis. (15) It has been shown that short-term infusions of aminoglycosides (once daily dosing) result in significantly decreased levels of renal cortical accumulation. (16,17) Ototoxicity is another commonly cited complication associated with aminoglycoside use. In animal studies, uptake of aminoglycosides in inner ear tissues was greater with continuous infusion than with single injection. (18) However, the clearance rate of aminoglycosides is slow, and it is possible that the prolonged exposure time of the sensory hair cells makes the dosage less important in the etiology of ototoxicity as compared with nephrotoxicity. (18) These findings have been corroborated in clinical studies in which the incidence of ototoxicity was equivalent between once daily dosin g versus multiple dosing of aminoglycosides. (19,20)
Clinical studies using large daily doses of aminoglycosides to treat established infections have shown good clinical responses without an increased complication profile. Koo et al, (21) in a randomized study evaluating elderly patients with various infections treated with once daily doses (4 mg/kg) of gentamicin or tobramycin compared with twice daily doses (2 mg/kg) of the same antibiotics, found no statistically significant difference in the clinical effectiveness between the two doses. Also, there was no difference in the incidence of nephrotoxicity between the two groups; however, in patients treated with once daily dosing, there was an increased incidence of nephrotoxicity in those patients whose initial peak serum concentration was greater than 12 mg/L. (21) Prins et al (19) compared once daily dosing of gentamicin (4 mg/kg) with thrice daily dosing (1.33 mg/kg) for various infections. The once daily regimen proved significantly less nephrotoxic (59% vs 24%), while preserving bacteriologic efficacy. Als o, high-tone audiometry showed no significant differences in hearing between the two groups. (19)
While the use of once daily gentamicin has proven effective in the treatment of established infections, its use as a prophylactic agent in open fractures has been described infrequently. Sorger et al (9) used 6 mg/kg of gentamicin given either once daily or twice daily, combined with cefazolin, for upper and lower extremity Gustilo types II and III open fractures. They found a decreased incidence of infections in patients who received the once daily dose of gentamicin; however, this finding did not reach statistical significance. Two patients who received twice daily gentamicin had transient elevation of serum creatinine, which returned to normal after discontinuance of antibiotics. No patient showed signs of ototoxicity.
The use of high, once daily dosing of gentamicin has been shown effective in our series of type II and type III open tibial shaft fractures in the prophylaxis against infection. The one superficial pin tract infection in a patient with a type II open fracture responded rapidly to oral antibiotics and improved pin care. Deep infections were seen in two patients (12.5%), one in a type IIIA fracture and one in a type IIIC fracture. There were no deep infections in patients with type II open fractures.
Many factors contribute to infections after open tibial shaft fractures, but higher infection rates are more commonly associated with higher energy injuries. (1,3,11,22-26) Both of our patients who had deep infections sustained high-energy injuries. One patient with a type IIIC open fracture stabilized with an external fixator had a deep wound infection necessitating multiple surgical debridements and intravenous antibiotics. The infection was not unexpected, and the postoperative course was not unusual. Several authors have reported series of open tibial fractures treated with external fixators. Court-Brown et al (22) reported infection in 6 of 37 patients with type IIIA open fractures treated with an external fixator. Other studies of high-energy tibial shaft fractures stabilized with external fixators reported infection rates of 7% to 15%. (23,25)
Our other patient with a deep wound infection sustained a type IIIA open fracture resulting from a gunshot wound and stabilized with a reamed intramedullary nail. The role of reamed intramedullary nails in the treatment of open tibial shaft fractures is controversial; however, several recent studies have shown acceptable infection rates using reamed intramedullary nails for open fractures. Court-Brown et al (22) reported infection in 2 of 27 patients with type III open tibial shaft fractures treated with reamed intramedullary nails. Keating et al, (24) in a randomized study comparing reamed nailing with unreamed nailing, found a slightly higher infection rate in the reamed nail group (4%) than in the unreamed group (2%), though the difference did not reach statistical significance.
Our study has several limitations. It is a retrospective review of patients given prophylaxis with once daily high-dose gentamicin without a well-established enrollment protocol. During the period under review, patients were given once daily, twice daily, or thrice daily gentamicin as ordered by the different physicians who treated these patients. While this series consists of a fairly homogeneous patient population, multiple surgeons and multiple implants were used. Patient follow-up was also problematic but merely reflects our transient trauma patient population.
Antimicrobial prophylaxis using once daily high-dose gentamicin in conjunction with cefazolin was found to be efficacious in our patients with high-energy open tibial shaft fractures. Once daily dosing of gentamicin permits higher serum peak concentrations and increased bactericidal action due to its concentration-dependent killing and the associated postantibiotic effect. (12-15) Once daily dosing of gentamicin leads to decreased renal accumulation of the drug, potentially decreasing the risk of nephrotoxicity. (16,17) No patient in this review had nephrotoxicity according to serologic monitoring of BUN and creatinine during hospitalization, and no patient showed any prodromal signs of ototoxicity.
We believe that in cases of open tibial shaft fractures, once daily high-dose gentamicin as prophylaxis against infection may be safely administered in patients who have a normal renal panel, are not pregnant, and have no renal disease, hearing loss, or granulocytopenia, without increased risk of nephrotoxicity or ototoxicity. On the basis of these results, we plan to initiate a prospective, multicenter study to further evaluate the role of once daily gentamicin for antimicrobial prophylaxis in open tibial shaft fractures.
(*.) Presented in part at the 17th Annual Meeting of the Southern Orthopaedic Association, Southampton, Bermuda, July 20, 2000.
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TABLE Patient Data in 16 Cases of Open Fractures of the Tibial Shaft Gustilo Fracture Wound Fracture Patient Type Injury Closure Treatment 1 IIIC Crush Rotation External flap fixator 2 IIIA Gunshot Delayed primary Unreamed closure nailing 3 IIIA Pedestrian- Delayed primary Unreamed auto closure nailing 4 II Motorcycle Rotation Unreamed accident flap nailing 5 IIIA Gunshot Delayed primary Reamed closure nailing 6 IIIB Pedestrian- Delayed primary Unreamed auto closure nailing 7 IIIA Motorcycle Delayed primary Unreamed accident closure nailing 8 II Motor vehicle Delayed primary Unreamed accident closure nailing 9 IIIC Pedestrian- Delayed primary External auto closure fixator 10 IIIA Motorcycle Primary Unreamed accident closure nailing 11 IIIB Crush Free flap Reamed nailing 12 II Motor vehicle Delayed primary Unreamed accident closure nailing 13 IIIB Motor vehicle Rotation 4.5 mm accident flap plate 14 IIIB Pedestrian- Free flap External auto fixator 15 IIIB Pedestrian- Rotation Unreamed auto flap nailing 16 IIIA Pedestrian- Delayed primary External auto closure fixator Union Injury Wound Follow-up Time Severity Patient Infection (no) (mo) Score 1 Staphylococcus 42 12 9 epidermidis, Serratia marcescens 2 None 40 2 22 3 None 34 28 13 4 None 17 12 9 5 Staphylococcus 17 9 13 aureus, Serratia marcescens 6 None 15 15 10 7 None 12 4 27 8 None 12 4 13 9 None 11 4 9 10 None 9 8 22 11 None 8 7 9 12 None 7 3.5 34 13 None 5 4 13 14 Pin tract 4 4 9 infection 15 None 3.5 3.5 22 16 None 3 3 22 Subsequent Patient Procedures 1 Irrigation and debridement x 4 2 None 3 Iliac crest bone grafting Exchanged nail Posterolateral iliac crest bone grafting 4 Dynamization Exchanged nail 5 Irrigation and debridement x 2 Exchanged nail Removed nail 6 Dynamization 7 None 8 None 9 None 10 Iliac crest bone grafting 11 Failed free flap with debridement 12 None 13 None 14 Adjusted external fixator 15 None 16 None
RELATED ARTICLE: KEY POINTS
* Once daily high-dose gentamicin in combination with Cefazolin was found to be an effective infection prophylaxis in high-energy open tibial shaft fractures.
* No patient sustained either ototoxicity or nephrotoxicity from once-daily high-dose gentamicin.
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|Author:||Pearsall, Albert W.|
|Publication:||Southern Medical Journal|
|Article Type:||Statistical Data Included|
|Date:||Dec 1, 2001|
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