Pharmacokinetics and burn eschar penetration of intravenous ciprofloxacin in patients with major thermal injuries

J. Esteban Varela, Stephen M. Cohn*, Margaret Brown, C. Gillon Ward, Nicholas Namias and Paul B. Spalding

Department of Surgery, Divisions of Trauma, Burns and Surgical Critical Care, University of Miami School of Medicine, PO Box 016960 (D-40) Miami, FL 33101, USA


    Abstract
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Adequate penetration of antibiotics into burn tissue and maintenance of effective serum levels are essential for the treatment of patients sustaining major thermal injuries. The pharmacokinetics and burn eschar penetration of intravenous ciprofloxacin were determined in 12 critically ill patients with burn injuries. Mean age for the 12 patients was 45 ± 17 (range 25–82 years), total body surface area burned (TBSAB) = 38 ± 15% and Acute Physiology and Chronic Health Evaluation (APACHE) II score = 8 ± 6. Patients received recommended doses of ciprofloxacin, 400 mg q12h iv, for three doses beginning 72 h post-burn. Serum concentrations were measured at t = 0, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 2.0, 4.0 and 12.0 h after the first and third doses. Burn eschar biopsies were obtained after the third ciprofloxacin dose. Three of these 12 patients (25%) manifested later signs of clinical sepsis (TBSAB = 61 ± 6% and APACHE II score = 11 ± 3) and underwent a second infusion of three doses of intravenous ciprofloxacin, blood sampling and eschar biopsy. Serum and eschar concentrations were determined by high performance liquid chromatography. Serum ciprofloxacin concentrations were comparable to those of normal volunteers (Cmax = 4.0 ± 1 mg/L and AUC = 11.4 ± 2 mg.h/L) during the immediate post-burn period after dose 1 (Cmax1 = 4.8 ± 3 mg/L and AUC0–12 = 12.5 ± 7 mg.h/L) and dose 3 (Cmax3 = 4.9 ± 2 mg/L and AUC24–36 = 17.5 ± 11 mg.h/L). Mean burn eschar concentration during the 72 h post-burn was significantly lower than that found during clinical sepsis (18 ± 17 compared with 41.3 ± 54 µg/g; P < 0.05 by t test). Similar serum concentrations were achieved in patients with clinical sepsis (Cmax1 = 4.2 ± 0.2 mg/L and AUC0–12 = 15.0 ± 3 mg.h/L; Cmax3 = 5.0 ± 1 mg/L and AUC24–36 = 22.8 ± 9 mg.h/L). A positive correlation between burn eschar concentrations and Cmax (r = 0.71, r2 = 0.51, P = 0.01) was found by linear regression analysis. A Cmax/MIC ratio > 10 (MIC = 0.5 mg/L) and an AUC/MIC ratio > 100 SIT–1.h (serum inhibitory titre) (MIC = 0.125 mg/L) were achieved. High burn eschar concentrations and serum levels, similar to those found in normal volunteers, can be achieved after intravenous ciprofloxacin infusion in critically ill burns patients.


    Introduction
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Sepsis remains one of the most serious complications of burn injury and a leading cause of death among patients with major thermal injuries. The most frequent sources of infection are the burn wound (80.8%) followed by air-borne infections (6.4%).1 More than 30 years ago it was demonstrated that the pathogenesis of burn wound sepsis is characterized by eschar colonization followed by bacterial invasion of underlying tissue and blood vessels, with or without distant haematogenous dissemination.2 Adequate penetration of antibiotics into the burn tissue and maintenance of effective serum levels are essential for treatment of burn wound infection. It has been described previously that the presence of burn injuries may induce many different pathological changes that alter pharmacokinetic parameters such as bioavailability, protein binding, volume of distribution and clearance.3

The bacterial kill produced by the quinolones is considered to be concentration dependent, and both Cmax (maximum concentration)/MIC (minimum inhibitory concentration) and AUC (area under the curve)/MIC ratios have been identified as predictors of clinical and microbiological outcome.4 High concentrations of ciprofloxacin, well above the MIC for most Gram-negative and Gram-positive aerobic bacteria, are reached in the skin and skin structures, suggesting that ciprofloxacin can be useful in the treatment of soft tissue infections.5 The ciprofloxacin concentrations obtained in inflammatory blisters, which are well above serum values6 and high penetration into skin blister fluid7 suggest that ciprofloxacin might penetrate into burned tissue.

It was decided to investigate the hypothesis that intravenously administered ciprofloxacin could reach adequate concentrations in serum and burn eschar in critically ill patients with burns. The pharmacokinetics of intravenous ciprofloxacin in patients sustaining major thermal injuries was studied, and the relationship between ciprofloxacin serum levels attained and concentration of the drug reaching the burn eschar was determined.


    Materials and methods
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Antibacterial agent

Ciprofloxacin (Bayer Corp., Pharmaceutical Division, West Haven, CT, USA) 400 mg was administered intravenously during the immediate post-burn period (within 72 h post-burn), and then every 12 h for a total of three doses. A 200 mL dilution (5% dextrose in water) was prepared and administered through a rate control device over 1 h.

Subjects

Prior approval for this protocol was obtained from the University of Miami School of Medicine Investigational Review Board and written informed consent was obtained for 12 patients. Subjects were included in the study on their first admission if they were at least 18 years of age, and had sustained second or third degree burns of more than 20% of their body surface area. Subjects were excluded from the study for any of the following reasons: (i) a history of hypersensitivity to quinolones, carbapenems or multivitamins; (ii) pregnant or lactating women; (iii) receipt of ciprofloxacin within 1 week of this study; (iv) receipt of another investigational drug within 30 days before drug administration; (v) renal impairment indicated by creatinine greater than 3.0 mg/dL or creatinine clearance less than 40 mL/min; (vi) significant liver dysfunction defined as total bilirubin greater than 3 mg%; (vii) granulocytopenia with granulocytes less than 1 x 109 cells/mL; (viii) history of a seizure disorder. Data regarding the subject's age, weight, pre-existing medical condition, total body surface area burn, infectious complications, multiple organ dysfunction syndrome (MODS) and acute physiology and chronic health evaluation (APACHE II) scores were recorded.

Patients developing clinical sepsis or SIRS (systemic inflammatory response syndrome) following their initial pharmacokinetic study underwent a second infusion of three doses of intravenous ciprofloxacin, blood sampling and burn eschar biopsies. SIRS was defined as the clinical picture of sepsis, with two or more of the following: temperature >38°C or <36°C; pulse >90 beats/min; respiratory rate >20 breaths/min or PaO2 <32 torr; WBC >12 x 109/L or <4 x 109/L or >10% immature (band) forms.8

Serum sampling

A 2 mL sample of blood was collected for drug assay from an existing arterial catheter before administration of the drug (baseline) and at 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 2.0, 4.0 and 12.0 h after doses one and three. Within 2 h of phlebotomy, samples were centrifuged (30 min at 3000 rpm) and the supernatant placed in cryogenic vials and stored in liquid nitrogen.

Tissue sampling

Biopsies (1 cm3) of the burn eschar were obtained at the time of surgery with a scalpel from two different burned sites, within 12 h of administration of the third dose of ciprofloxacin. These concentrations were averaged. For the purpose of determining the amount of ciprofloxacin reaching the burn eschar, these were placed in cryogenic vials and stored in liquid nitrogen. Serum and tissue samples were shipped on dry ice to Bayer Corporation for drug assay.

Assay

Ciprofloxacin assay was performed (Bayer Corporation, Pharmaceutical Division, Clinical Pharmacology Laboratory, West Haven, CT, USA). Serum and eschar concentrations were determined by high-performance liquid chromatography (HPLC).9 Each 0.5 mL aliquot of the serum or tissue samples was diluted with 0.1 mL of a 0.02 mg/mL solution of internal standard in 0.1 M phosphoric acid and 0.3 mL of 5.0 M trichloroacetic acid–acetonitrile (1:1, v:v) solution. The mixture was vortexed and centrifuged for 15 min at 2800 rpm (1500g). The supernatant was transferred with a Pasteur pipette into a glass autosampler vial for HPLC analysis. Quantifications of ciprofloxacin and ciprofloxacin metabolite concentrations were based on the relative peak height response ratios of each compound and the internal standard.

Pharmacokinetic analysis

Pharmacokinetic variables were determined using non-compartmental models. Maximum serum concentrations and time to maximum serum concentration were determined directly from the serum concentration–time curve derived from the data observed following the first and last dose (steady state). The area under the curve value for each dose interval was determined by the log-linear trapezoidal method.

Statistical analysis

Values are mean ± standard error of the mean (s.e.m.). Between-group statistical analysis was performed by analysis of variance (Anova), using a statistical software package (Statistica, Statsoft Inc., Tulsa, OK, USA). Least square linear regression analysis was used to assess correlation between burn eschar and serum concentrations. The strength of the linear relationship between variables is given by r2 values. Comparisons between straight-line regressions were performed by two-sided Student's t test and statistical significance was determined by P < 0.05.


    Results
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Twelve burn patients (five females, seven males) were included in this study. Mean age was 45 ± 17 (range 25–82 years) and the mean total body weight was 78 ± 13 kg. Mean total body surface area burned (TBSAB) was 38 ± 15% (range 22–65%). Mean APACHE II score on admission was 8 ± 6 (range 2–27). Third degree burns were present in eight patients. Renal function was universally normal on study entry with a mean serum creatinine of 0.9 ± 0.3 mg/dL. Mean intravenous fluid resuscitation requirement was 29 ± 12 L for the first 72 h. Three patients manifested signs of clinical sepsis (respiratory tract infection, MODS and cellulitis) 13 ± 6 days after the first ciprofloxacin dose was administered and presented with a mean TBSAB of 61 ± 6% (range 55–65%) and a mean APACHE II score of 11 ± 3 (range 7–14). Three patients died during the study period (MODS, acute mesenteric ischaemia and acute respiratory failure) but these deaths were unrelated to ciprofloxacin administration.

Mean maximum serum concentration (Cmax) (mg/L) for dose 1 (Cmax1) and dose 3 (Cmax3), area under the serum concentration versus time curve (AUC) (mg.h/L) from t = 0 to 12 h (AUC0–12), t = 24–36 h (AUC24–36) and eschar concentrations (µg/g) during 72 h post-burn and clinical sepsis are listed in Table IGo. A moderate variability in pharmacokinetic parameters was observed for Cmax (range 2.7–11.4 mg/L) and AUC (range 7.2–32.1 mg.h/L) during the post-burn period and during clinical sepsis. Ciprofloxacin serum concentrations during 72 h post-burn after dose 1 (Cmax1 = 4.8 ± 3 mg/L and AUC0–12 = 12.5 ± 7 mg.h/L) and dose 3 (Cmax3 = 4.9 ± 2 mg/L and AUC24–36 = 17.5 ± 11 mg.h/L) were comparable to those of normal volunteers.10 Similar serum concentrations were obtained during clinical sepsis after dose 1 (Cmax1 = 4.2 ± 0.2 mg/L and AUC0–12 = 15.1 ± 3 mg.h/L) and dose 3 (Cmax3 = 5.0 ± 1 mg/L and AUC24–36 = 22.8 ± 9 mg.h/L; 41.3 ± 54 µg/g) (see Figure 1Go). Rarely however, were Cmax or AUC values less than those found in normal volunteers. Variability in eschar concentrations was also noted (range 3.8–103.5 µg/g) in both groups. Mean burn eschar concentration during clinical sepsis was significantly higher than that found at 72 h post-burn (41.3 ± 54 compared with 18 ± 17 µg/g; P < 0.05 by t test). A positive correlation between burn eschar concentrations and Cmax (r = 0.71, r2 = 0.51, P = 0.01) was found by linear regression analysis. Straight-line regressions are shown in Figure 3Go. A Cmax/MIC ratio > 10 for an assumed MIC = 0.5 mg/L and an AUC/MIC ratio > 100 SIT–1.h (serum inhibitory titre) for an assumed MIC = 0.125 mg/L were achieved (Tables II and IIIGoGo).


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Table I. Mean pharmacokinetic values ± S.D. within 72 h post-burn (n = 12) and clinical sepsis (n = 3)
 


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Figure 1. Mean ciprofloxacin serum concentration (mg/L) ± S.E.M. versus time (h) within 72 h post-burn for doses 1 (circle) and 3 (triangle).

 


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Figure 3. Straight-line regression for burn eschar concentration and Cmax3 (mg/L) (eschar = –15.0 + 6.7 x Cmax).

 

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Table II. Cmax/MIC ratios ± S.D. for representative MICs (mg/L) within 72 h post-burn (n = 12) and clinical sepsis (n = 3)
 

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Table III. AUC/MIC ratios (SIT–1.h) ± S.D. for representative MICs (mg/L) within 72 h post-burn (n = 12) and clinical sepsis (n = 3)
 

    Discussion
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The principal findings of this study were: (i) intravenous administration of ciprofloxacin 400 mg q12h, resulted in serum concentrations comparable to those found in normal volunteers, in patients with major thermal injuries, in both the immediate post-burn period and during clinical sepsis; (ii) burn eschar concentrations attained after intravenous ciprofloxacin infusion were significantly higher than Cmax values; (iii) burn eschar levels were positively correlated with serum concentrations.

It is known that major thermal injury can result in increased clearance of antibiotics that are primarily excreted by the kidney and decreased clearance of antibiotics undergoing significant hepatic oxidation.3 Therefore, antibiotic dosing adjustments are usually required after major burns because of the pharmacokinetic alteration that occurs in this setting. Clinical trials for ceftazidime, ticarcillin, piperacillin and aztreonam have demonstrated increases in volumes of distribution and decreases in maximum concentrations of antibiotics achieved.11

A study in normal volunteers demonstrated ciprofloxacin Cmax and AUC values, after a 400 mg iv dose, similar to the corresponding values observed in our study: Cmax = 4.0 ± 0.6 mg/L and AUC = 11.4 ± 1.6 mg.h/L.10 Garrelts et al. evaluated prospectively the pharmacokinetics of ciprofloxacin in eight burn patients with active infections. Each patient received a 400 mg iv dose of ciprofloxacin every 8 h.12 They observed a highly variable and increased clearance of the drug. Although this study suggested a more frequent dosage regimen and was performed after the resuscitative phase (mean 8 days) following burn injury, pharmacokinetic parameters (Cmax = 4.2 ± 1 mg/L and AUC = 20.7 ± 17 mg.h/L) were similar to those found in the present investigation.

Evaluations of penetration of burned tissue have been described only for gentamicin13 and tobramycin.14 These studies suggested that a concentration of aminoglycoside sufficient to prevent proliferation of organisms cultured from the eschar was obtained and that eradication of organisms was due to concentrations achievable at this site. Ristuccia et al. found a positive correlation between gentamicin burn tissue concentrations and AUC.14 Burn eschar concentrations and Cmax3 and AUC24–36 values correlated in this study despite some variability in eschar and serum concentrations.

High ciprofloxacin concentrations were reached in the burn eschar in this study, which were higher than those measured in the serum (Cmax). This finding may be attributable to the large volume of distribution of ciprofloxacin after intravenous dosing and the two-compartment model, which reflects penetration of the drug into most tissues including the burn eschar.15 Variability in eschar concentrations may reflect viability of tissue sampled as well as biopsy depth. Although there are few previous data, our findings are comparable with studies by Bergan, where the total ciprofloxacin concentration for inflammatory blisters was 120% of the serum values6 and with studies demonstrating that penetration of ciprofloxacin into skin blister fluid can be as high as 96%.7

Pharmacokinetic and burn eschar values in septic patients were similar to those in non-septic patients. The low number of patients and inter-subject variation mean that no definitive statements about this subgroup can be made. Quinolones have been shown to exhibit concentration-dependent killing for Gram-negative organisms. Studies have demonstrated that Cmax/MIC and AUC/MIC ratios are important predictors of bacterial killing for these antimicrobial agents. Area under the inhibitory concentration–time curve (AUIC24) (i.e. AUC24/MIC) is a useful parameter for describing efficacy of these agents, while an adequate peak concentration/MIC ratio seems necessary to prevent selection of resistant organisms.4 Investigators have suggested that those AUC24/MIC ratios of >=100–125 SIT–1.h and Cmax/MIC ratios of >=10:1 predict clinical and microbiological success.16 In this study, a Cmax/MIC ratio >=10 for an assumed MIC = 0.5 and an AUC/MIC ratio >=100 SIT–1h for an assumed MIC = 0.125 mg/L were achieved. MICs were chosen as representative values for organisms encountered when treating infections in critically ill burn patients. These data, in addition to the fact that excellent eschar penetration was found, suggest that therapeutic ciprofloxacin serum concentrations can be achieved in critically ill burned patients.

There were some limitations in our study: first, MIC susceptibility testing for pathogens isolated from burn eschar was not performed. Instead representative MICs were considered. Secondly, there was some potential variation in the amount of viable tissue included in each biopsy, as well as the time interval between dose three and biopsy, and lastly, there was heterogeneity in age, total body surface, weight, burn size and intravenous fluids required for resuscitation in this group, which may have contributed to some variability in serum and burn eschar values.

In summary, after recommended doses of intravenous ciprofloxacin, high burn eschar concentrations and similar serum concentrations to those achieved by normal volunteers, are reached in patients sustaining major thermal injuries, in the immediate post-burn period and during clinical sepsis.



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Figure 2. Mean ciprofloxacin serum concentration (mg/L) ± S.E.M. versus time (h) in clinical sepsis for doses 1 (circle) and 3 (triangle).

 

    Acknowledgments
 
We would like to thank Drs D. Dunn, S. Kowalsky, J. Lettieri, B. Pruitt and J. Rotschafer for their thoughtful reviews of this manuscript. This study was presented at The Society of University Surgeons, Forty-First Annual University Surgical Residents Conference, New Orleans, LA, February 11–12, 1999. Bayer Corporation, Pharmaceutical Division, Clinical Pharmacology Laboratory, West Haven, CT provided funding for this study.


    Notes
 
* Corresponding author. Tel: +1-305-585-1185; Fax: +1-305-326-7065; E-mail: stephen.cohn{at}miami.edu Back


    References
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
1 . Herndon, D. N. (1996). The burn problem: a pathologist's perspective. In Total Burn Care, (Herndon, D. N., Ed.), pp. 370–81. W. B. Saunders Company Ltd, London.

2 . Teplitz, C. (1965). Pathogenesis of Pseudomonas vasculitis and septic lesions. Archives of Pathology 80, 297–307.[ISI][Medline]

3 . Jaehde, U. & Sorgel, F. (1995). Clinical pharmacokinetics in patients with burns. Clinical Pharmacokinetics 29, 15–28.[ISI][Medline]

4 . Hyatt, J. M., McKinnon, P. S., Zimmer, G. S. & Schentag, J. J. (1995). The importance of pharmacokinetic/pharmacodynamic surrogate markers to outcome. Focus on antibacterial agents. Clinical Pharmacokinetics 28, 143–60.[ISI][Medline]

5 . Andriole, V. T. (1988). Clinical overview of the newer quinolone antibacterial agents. In The Quinolones, (Andriole, V. T., ed.), pp. 155–200. Academic Press Limited, San Diego, CA.

6 . Bergan, T. (1990). Extravascular penetration of ciprofloxacin: a review. Diagnostic Microbiology and Infectious Disease 13, 103–14.[ISI][Medline]

7 . Lubowski, T. J., Nightingale, C., Sweeney, K., Quintiliani, R. & Zhi, J. (1992). Penetration of fleroxacin and ciprofloxacin into skin blister fluid: a comparative study. Antimicrobial Agents and Chemotherapy 36, 651–5.[Abstract]

8 . American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference: (1992). Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Critical Care Medicine 20, 864–74.[ISI][Medline]

9 . Krol, G. J., Noe, A. J. & Beerman, D. (1986). Liquid chromatographic analysis of ciprofloxacin metabolites in body fluids. Journal of Liquid Chromatography 9, 2897–19.[ISI]

10 . Lettieri, J. T., Rogge, M. C., Kaiser, L., Echols, R. M. & Heller, A. H. (1992). Pharmacokinetic profiles of ciprofloxacin after single intravenous and oral doses. Antimicrobial Agents and Chemotherapy 36, 993–6.[Abstract]

11 . Boucher, B. A., Kuhl, D. A. & Hickerson, W. L. (1992). Pharmacokinetics of systemically administered antibiotics in patients with thermal injury. Clinical Infectious Diseases 14, 458–63.[ISI][Medline]

12 . Garrelts, J. C., Jost, G., Kowalsky, S. F., Krol, G. J. & Lettieri, J. T. (1996). Ciprofloxacin pharmacokinetics in burn patients. Antimicrobial Agents and Chemotherapy 40, 1153–6.[Abstract]

13 . Ristuccia, A. M., Gayle, W. E., Wasserman, A. J. & Cunha, B. A. (1982). Penetration of gentamicin in burn wounds. Journal of Trauma 22, 944–9.[ISI][Medline]

14 . Polk, R. E., Mayhall, C. G., Smith, J., Hall, G., Kline, B. J., Swensson, E. et al. (1983). Gentamicin and tobramycin penetration into burn eschar. Archives of Surgery 118, 295–301.[Abstract]

15 . Vance-Bryan, K., Guay, D. R. & Rotschafer, J. C. (1990). Clinical pharmacokinetics of ciprofloxacin. Clinical Pharmacokinetics 19, 434–61.[ISI][Medline]

16 . Drusano, G. L., Johnson, D. E., Rosen, M. & Standiford, H. C. (1993). Pharmacodynamics of a fluoroquinolone antimicrobial agent in a neutropenic rat model of Pseudomonas sepsis. Antimicrobial Agents and Chemotherapy 37, 483–90.[Abstract]

Received 28 April 1999; returned 9 August 1999; revised 6 September 1999; accepted 26 October 1999