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Influence of experimental rat model of multiple organ dysfunction on cefepime and amikacin pharmacokinetics

  • Centre Hospitalo-universitaire de la Martinique


We adapted an experimental model of multiple organ dysfunction to study the alterations it induces in the pharmacology of cefepime and amikacin. The half-lives of both antibiotics were significantly prolonged because of nonsignificant enhancement of the volume of distribution and reduced renal elimination. In the presence of multiple organ dysfunction, the concentration of each antibiotic in the lungs, compared with that in the lungs of healthy controls, was significantly decreased, despite similar concentrations in plasma, indicating that the application of a standard antibiotic concentration in plasma could lead to underdosage in tissues during the initial days of therapy.
ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Mar. 1996, p. 819–821 Vol. 40, No. 3
Copyright q 1996, American Society for Microbiology
Influence of Experimental Rat Model of Multiple Organ Dysfunction
on Cefepime and Amikacin Pharmacokinetics
Service d’Anesthe´sie-Re´animation Chirurgicale,
and Service d’Anatomo-Pathologie,
Hoˆpital Biceˆtre,
94270 Le Kremlin-Biceˆtre, and Cre´pit 93, Centre de Recherche en Pathologie Infectieuse
et Tropicale,
and De´partement de Pharmacologie-Toxicologie Hospitalie`re,
Hoˆpital Avicenne, 93009 Bobigny, France
Received 8 August 1995/Returned for modification 28 September 1995/Accepted 6 December 1995
We adapted an experimental model of multiple organ dysfunction to study the alterations it induces in the
pharmacology of cefepime and amikacin. The half-lives of both antibiotics were significantly prolonged because
of nonsignificant enhancement of the volume of distribution and reduced renal elimination. In the presence of
multiple organ dysfunction, the concentration of each antibiotic in the lungs, compared with that in the lungs
of healthy controls, was significantly decreased, despite similar concentrations in plasma, indicating that the
application of a standard antibiotic concentration in plasma could lead to underdosage in tissues during the
initial days of therapy.
Previous studies have shown that the pharmacokinetic pa-
rameters of aminoglycosides are profoundly modified in inten-
sive care unit patients, but little is known about other classes of
antibiotics, such as b-lactams (16). In this study, we adapted an
experimental model described by Goris et al. (5) by injecting
smaller doses of zymosan to evaluate the multiple organ dys-
function-induced pharmacokinetic modifications of a new b-
lactam, cefepime, in plasma and lungs. Amikacin was also
studied to compare the pharmacokinetic modifications in-
duced by our model with those observed in humans and thus to
determine whether it could constitute a valuable model.
Experimental multiple organ dysfunction. Twenty Wistar
rats were randomly assigned to a zymosan group or a healthy
group (10 per cohort). Each rat in the former group received
an intraperitoneal (i.p.) injection of 0.5 mg of zymosan (Sigma)
per g suspended in liquid paraffin to induce a chronic release of
inflammatory mediators, which resulted in maximal multiple
organ dysfunction 12 days later. Previous studies showed that
all of the surviving animals 12 days after zymosan challenge
improved until complete recovery. Because zymosan induced
acute peritonitis during the first 3 days after its administration,
0.1 mg of imipenem-cilastatin (Merck Sharp and Dohme-Chi-
bret) per g was administered simultaneously to diminish the
initial mortality due to overwhelming infection. No i.p. injec-
tion was given to rats in the healthy group which served as a
control. To simulate further the human situation, all rats re-
ceived i.p. injections of 0.9 M saline equal to 0.025 ml/g on days
0, 1, 2, 9, 10, and 11 following randomization. Clinical condi-
tions were recorded daily, and on day 12, all surviving rats were
anesthetized and bled by aortic puncture to determine biolog-
ical parameters, and the lungs, kidneys, spleen, liver, and a part
of the digestive tract were removed and weighted. Relative
organ weights were calculated by using the formula (organ
weight/body weight) 3 100. After fixation with 4% formalde-
hyde, microscopic sections of these organs were prepared for
staining with hematoxylin-eosin-saffron and examined (n 5 six
per group). Studies of cefepime and amikacin (Bristol-Myers
Squibb) pharmacokinetics were performed when multiple or-
gan dysfunction was well established, i.e., 12 days after i.p.
injection of zymosan, and the results were compared with those
of similar studies with healthy rats.
Pharmacokinetic parameters. Each rat (five or six per
group) received a single 1-ml i.p. injection of either 50 mg of
cefepime per kg or 18 mg of amikacin per kg. Multiple blood
samples (300 ml) were collected 30, 60, 90, 120, 150, 180, 240,
300, and 360 min after antibiotic injection. Saline (600 ml) was
injected intraarterially after collection of each blood sample to
restore blood volume. Individual cefepime and amikacin phar-
macokinetic parameters were determined. The peak concen-
tration in plasma and the time it took to reach that peak were
the experimental values. A noncompartmental model was used
to fit the data by weighted least squares with the weighting
factor 1/y
to determine half-life, volume of distribution in
the b phase total body clearance, and the area under plasma
concentration-time curve extrapolated to infinity for cefepime
and amikacin in healthy rats and rats with multiple organ
dysfunction, taking the fraction of the cefepime or amikacin
dose absorbed to be equal to 1 (Siphar).
Antibiotic concentrations in lung tissue. Six to 10 other rats
per group were sacrificed 1, 2, and 3 h after being given a single
1-ml i.p. injection of 50 mg of cefepime per kg and 18 mg of
amikacin per kg. Blood was collected to determine the antibi-
otic concentration in plasma. The lungs were homogenized in
1 ml of saline, and the resulting suspension was centrifuged for
10 min at approximately 1,000 3 g and 38C. The supernatant
was collected, and antibiotic levels were assayed. Antibiotic
measurements were not corrected for blood contamination
because blood represents less than 6% of lung weight and
neither antibiotic accumulated in erythrocytes; therefore, the
presence of blood does not lead to substantial errors in the
evaluation of amikacin or cefepime levels (11).
Measurement of antibiotic concentrations. The cefepime
concentration was determined by using a modified version of
the high-performance liquid chromatography assay described
by Barbhaiya et al. (2). The quantification limit of the assay was
1 mg/liter, and the between-days coefficient of variation ranged
from 7% at 1 mg/liter to 6% at 50 mg/liter. The amikacin
concentration was determined by using an immunoenzyme as-
* Corresponding author. Phone: (33) 1 45213441. Fax: (33) 1
say (EMIT assay). The limit of quantification was 1 mg/liter,
and the coefficients of variation were below 8% over the entire
range of measurement. The biological matrices used for high-
performance liquid chromatography and EMIT standards were
bovine plasma for plasma samples and water for tissue sam-
Statistical analysis. Results are expressed as medians with
ranges. Data from healthy rats and rats with multiple organ
dysfunction were compared by using the Mann-Whitney U
test. A P value below 0.05 was considered to be significant.
From days 1 to 4, all rats in the zymosan group showed
symptoms of illness. They became lethargic and anorexic, hy-
perventilated, and had ruffled fur and diarrhea. Epistaxis and
bleeding conjunctivae were also observed. From days 4 to 8,
the rats improved, becoming very active, gaining weight, and
no longer hemorrhaging or having diarrhea. Between days 9
and 12, their general condition deteriorated again, with in-
creasing hyperventilation, tachycardia, and loss of weight. All
control rats remained healthy throughout the experimental
period and progressively gained weight. One zymosan group
rat died on day 10. The remaining 19 rats were sacrificed on
day 12 for biological and histological studies. Premortem ex-
amination showed that healthy rats gained significantly more
weight during the study period than did rats with multiple
organ dysfunction (7.8 versus 1.5%; P , 0.002). Postmortem
examination of rats with multiple organ dysfunction showed
signs of extensive acute peritonitis, edematous lungs, pale liver,
and large spleen, whereas postmortem examination results of
healthy rats were normal. As shown in Table 1, in the presence
of multiple organ dysfunction, the relative weights of each
organ was significantly increased, indicating increased water
content. The results of blood analyses are summarized in Table
2. Experimentally induced multiple organ dysfunction gener-
ated several microscopic modifications in different organs.
Lung specimens showed thickening of alveolar walls, edema,
and infiltrates of mononuclear cells. Kidney specimens exhib-
ited focal necrosis of proximal tubules and edema. Spleens
were depleted of lymphoid tissue, while the numbers of mega-
karyocytes and erythroblasts were increased. Liver specimens
showed engorged veins, inflammatory lymphocyte infiltrates,
and hyperplasia of Kupffer cells. The wall of the small intestine
specimen was infiltrated by mononuclear cells.
Cefepime and amikacin pharmacokinetic parameters in
healthy animals were similar to those previously reported (Ta-
ble 3). For both antibiotics, the presence of multiple organ
dysfunction significantly increased the antibiotic elimination
half-lives because of nonsignificant enhancement of the vol-
ume of distribution and reduced renal elimination (Table 3).
Despite similar concentrations of the two antibiotics in plasma
in both study groups, their concentrations in the lungs were
significantly lower in rats with multiple organ dysfunction 1 and
2 h after administration (Table 4). No antibiotic was detected
in the lungs 3 h after injection.
Experimental models of multiple organ dysfunction in small
laboratory animals generally utilize a bacterial or endotoxin
challenge (7, 12, 17). The mortality induced by these models is
high. Recently, Goris et al. (5) developed an experimental
animal model of multiple organ dysfunction that we adapted by
using a lower dose of zymosan to stimulate the human clinical
syndrome by its prolonged activation of the alternative com-
plement pathway and macrophages induced by an i.p. injection
of zymosan into the rats (5). Twelve days after zymosan injec-
tion, the clinical, biochemical, and microscopic alterations in
our model closely resembled those reported in critically ill
septic patients and in other animal models of bacterium or
endotoxin-induced multiple organ dysfunction (5). Impor-
tantly, mortality in our model was relatively low in comparison
with that observed in previously reported models. Modifica-
TABLE 1. Comparison of relative organ weights between healthy
rats and those with multiple organ dysfunction
Median relative organ wt (range)
P value
Healthy rats
(n 5 10)
Rats with multiple
organ dysfunction
(n 5 9)
Lung 0.4 (0.3–0.4) 0.7 (0.4–0.9) 0.002
Liver 3.3 (2.8–3.7) 4.0 (3.6–4.7) 0.002
Kidney 0.6 (0.5–0.6) 0.7 (0.6–0.8) 0.009
Spleen 0.2 (0.2–0.4) 0.7 (0.5–1.1) 0.001
TABLE 2. Comparison of blood analysis results of healthy
rats and rats with multiple organ dysfunction
Biological parameter
Median (range)
P value
Healthy rats
(n 5 10)
Rats with multiple
organ dysfunction
(n 5 9)
(mm Hg) 92 (82–103) 77 (65–90) 0.01
Glycemia (mmol/liter) 9.1 (7.2–11.3) 7.0 (4.3–9.1) 0.003
Creatinine (mmol/liter) 54 (38–58) 51 (43–55) 0.5
Alkaline phosphatase
92 (69–114) 127 (85–150) 0.003
Bilirubin (U/liter) 7 (4–19) 12 (4–14) 0.2
Leukocytes (10
/liter) 3.0 (1.6–8.2) 5.4 (3.7–8.2) 0.02
Polymorphonuclear leuko-
cytes (%)
37 (16–61) 60 (55–72) 0.004
Lymphocytes (%) 59 (36–78) 35 (22–42) 0.003
Hematocrit (%) 41 (39–46) 37 (35–38) 0.001
Thrombocytes (10
/liter) 710 (532–852) 1,263 (1,086–1,486) 0.001
TABLE 3. Pharmacokinetic parameters measured in plasma after
i.p. injection of 50 mg of cefepime per kg or 18 mg of amikacin per
kg into healthy rats or rats with multiple organ dysfunction
Drug and
Median (range)
P value
Healthy rats
Rats with multiple
organ dysfunction
(mg/liter) 54 (39–83) 78 (60–94) 0.17
(min) 30 (30–60) 30 (30–30) 0.21
(liters/kg) 0.4 (0.4–0.5) 0.5 (0.4–0.8) 0.27
(ml/min z kg) 7.2 (6.3–7.3) 6.7 (4.3–9.6) 0.29
(h) 0.7 (0.6–0.8) 0.9 (0.7–1.0) 0.05
AUC (h z mg/liter) 116 (113–131) 123 (96–195) 0.37
(mg/liter) 18 (15–41) 24 (22–27) 0.34
(min) 30 (30–30) 30 (30–30) 1
(liters/kg) 0.6 (0.3–0.8) 0.7 (0.5–0.9) 0.37
(ml/min z kg) 8.7 (4.3–9.8) 5.3 (3.5–7.2) 0.15
(h) 0.9 (0.9–1) 1.2 (1–2.4) 0.01
AUC (h z mg/liter) 35 (31–70) 57 (42–86) 0.15
, peak concentration in plasma; T
, time to peak concentration in
plasma; V
, volume of distribution in the b phase; CL
, total body clearance;
; half-life during the b phase; AUC, area under the plasma concentration-
time curve.
There were seven healthy rats in the cefepime group and six in the amikacin
There were six rats each with multiple organ dysfunction in the cefepime and
amikacin groups.
tions of cefepime and amikacin pharmacokinetics induced by
our experimental multiple organ dysfunction were comparable,
with significantly increased half-lives and nonsignificant en-
hancement of the volume of distribution. Expanded volumes of
distribution and prolonged half-lives of aminoglycosides and
some b-lactams (including cefepime) have already been re-
ported for critically ill subjects (1, 3, 6, 9, 10, 15, 16). The
increase in the volume of distribution is largely explained by
the enhancement of extracellular fluid following endothelial
damage and tissue edema (4, 13). The slight increase in the
volume of distribution in our model compared with that ob-
served in humans could be explained by the lack of various
factors affecting pharmacokinetic parameters, i.e., massive vol-
ume expansion, mechanical ventilation, positive end-expiratory
pressure, fever, old age, etc., which could not be reproduced in
our model (8, 14). The addition of an experimental infection,
which could modify per se the pharmacokinetic parameters of
both antibiotics and emphasize the modifications observed (es-
pecially enhancement of the volume of distribution could be
expected), needs to be addressed. The variability of the phar-
macokinetic parameters observed in animals with multiple or-
gan dysfunction was not greater than in healthy rats, which is
different from reported findings on humans. However, inten-
sive care unit patients do not form a homogeneous population
and the gravity of the illness varies from one patient to an-
other. By contrast, with the same dose of zymosan the intensity
of inflammatory system stimulation was similar among all of
the animals, and this can explain the lack of great variability
among pharmacokinetic parameters in rats with multiple organ
Concentrations of both antibiotics in the lungs were signif-
icantly lower in rats with multiple organ dysfunction than
in healthy rats, despite similar concentrations measured in
plasma. Even if we were unable to confirm that antibiotic
concentrations in the extracellular fluid proportionally de-
crease with regard to antibiotic concentrations in whole tissue,
in light of our results we can assume it. Multiple organ dys-
function induces an increase in the water content of organs
(Table 1) that is located primarily in the extracellular space (4,
13). Since b-lactams and aminoglycosides are distributed in the
total extracellular water, the proportion of fluid containing
antibiotics was increased and the apparent antibiotic level in
the whole tissue should have increased, but the opposite was
observed, suggesting that antibiotic concentrations in the ex-
tracellular space were decreased in animals with multiple or-
gan dysfunction. Decreased blood flow to the tissues, as ob-
served in humans and other experimental models (12, 17),
could explain, at least in part, the results observed.
Our finding that in the presence of multiple organ dysfunc-
tion, concentrations of both antibiotics in the lungs were sig-
nificantly decreased, despite their similar concentrations in
plasma, suggests that the recommendation of a standard anti-
biotic concentration in plasma could lead to suboptimal con-
centrations in tissues during the initial days of therapy. These
pharmacokinetic alterations need to be confirmed, and their
effects in an experimental model of infection must be evalu-
We thank R. J. A. Goris and Monique Jansen for help with the
adaptation of the zymosan model and P. Norwood for rereading the
We thank Bristol-Myers Squibb (France) for supporting this work.
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TABLE 4. Concentrations of cefepime or amikacin in plasma and
lungs measured 1, 2, and 3 h after antibiotic administration in
healthy rats and rats with multiple organ dysfunction
Time after
drug ad-
tion (h)
and site
No. of rats, median cefepime
No. of rats, median amikacin
Rats with mul-
tiple organ
Rats with mul-
tiple organ
Plasma 10, 57 (21–82) 9, 76 (40–97) 10, 26 (20–39) 9, 22 (16–36)
Lungs 10, 23 (8–28) 9, 13 (7–15)
10, 4 (3–6) 9, 2 (2–2)
Plasma 10, 35 (26–38) 8, 29 (20–38) 10, 9 (7–16) 8, 13 (10–16)
Lungs 10, 9 (3–13) 8, 3 (2–6)
10, ,18,,1
Plasma 6, 19 (9–28) 6, 13 (9–18) 6, 5 (3–7) 6, 7 (5–9)
Lungs 6, ,16,,16,,16,,1
Concentrations in plasma are in milligrams per liter. Concentrations in lung
tissue are in micrograms per gram.
P , 0.05 for rats with multiple organ dysfunction versus healthy rats for the
antibiotic given.
VOL. 40, 1996 NOTES 821
... Even in the absence of overt renal or liver dysfunction, the pharmacokinetics may be altered in trauma, burn or septic patients. Moreover, organic impairment may be unstable, reanimation and support procedures may further affect metabolism, and profound individual variability has been described [1,2,3]. Most of these specific patient subpopulations are studied after marketing, usually with financial support from the manufacturer, by a few experts and on very small numbers of patients, partly because of cost constraints. ...
... Serum levels are generally better predictors of extracellular interstitial fluid concentrations than tissue homogenates and are clinically relevant because most bacterial pathogens are extracellular but serum levels will have a tendency to overestimate the peak/MIC ratio and underestimate the T >MIC . In an experimental rat model of multiple organ dysfunction, Mimoz showed lower lung concentration in ill animals compared to controls despite similar plasma levels [2]. ...
... My conclusions would be that [1] pharmacodynamic studies are necessary better to understand the interactions between the infected or colonised host and antibiotics, but that additional refinements of the pharmacodynamic parameters are still needed [2]. One must be very careful when interpreting the results and the conclusions of available data [3] because data are scarce. ...
... Our results showed that EMB had very strong lung penetration (107%), however, AMK was very weak (0.1%). The C max of AMK in lung detected in this work was similar to that previously reported [29,30]. Our results indicate that the developed method was available to detect the concentration of EMB and AMK in the lung tissues from MDR-TB patients. ...
... 2. Sur le plan pharmacologique, la dose unique journalière pallie les risques de sous-dosage majorés par les conséquences des syndromes inflammatoires. Cette dose compense en effet l'augmentation du volume de distribution des médicaments et favorise la diffusion tissulaire contre le gradient électrochimique[4]. 3. Sur le plan toxicologique, la disproportion entre la quantité d'aminoside et les possibilités de captation par les organes cibles expliquent une faible pénétration après dose unique journalière car les hautes concentrations sont brèves alors que des concentrations adaptés aux possibilités de captation persistent longtemps après injections multiples. ...
... 17,18 Reduction of the bactericidal activities of both antibiotics due to this inoculum effect at higher bacterial titre could be favoured by the low antibiotic concentration measured in the lungs (Table I); such low cefepime and amikacin concentrations have previously been observed in the lungs of critically ill animals. 19 Both the inoculum effect and low antibiotic concentration could explain the weak in-vivo reduction of the lung bacterial titre, even when both antibiotics were used in combination, and could be predicted by our time-kill curves ( Figure 2). These two phenomena could be important factors in the management of infections involving high bacterial concentrations, suggesting that increasing the antibiotic dose and using antibiotic combinations could be advantageous when treating such infections. ...
Full-text available
The activities of cefepime and amikacin alone or in combination against an isogenic pair of Enterobacter cloacae strains (wild type and stably derepressed, ceftazidime-resistant mutant) were compared using an experimental model of pneumonia in non-leucopenic rats. Animals were infected by administering 8.4 log10 cfu of E. cloacae intratracheally, and therapy was initiated 12 h later. At that time, the animals' lungs showed bilateral pneumonia and contained more than 7 log10 E. cloacae cfu/g tissue. Because rats eliminate amikacin and cefepime much more rapidly than humans, renal impairment was induced in all animals to simulate the pharmacokinetic parameters of humans. In-vitro susceptibilities showed an inoculum effect with cefepime proportional to the bacterial titre against the two strains, but more pronounced with the stably derepressed mutant strain, whereas with bacterial concentrations of up to 7 log10 cfu/mL, no inoculum effect was observed with amikacin. In-vitro killing indicated that antibiotic combinations were synergic only at intermediate concentrations. At peak concentrations, the combination was merely as effective as amikacin alone. At trough concentrations, a non-significant trend towards the superiority of the combination over each antibiotic alone was noted. Moreover, cefepime was either bacteriostatic or permitted regrowth of the organisms in the range of antibiotic concentrations tested. Although each antibiotic alone failed to decrease bacterial counts in the lungs, regardless of the susceptibility of the strain used, the combination of both antibiotics was synergic and induced a significant decrease in the lung bacterial count 24 h after starting therapy when compared with tissue bacterial numbers in untreated animals or animals treated with either antibiotic alone. No resistant clones emerged during treatment with any of the antibiotic regimens studied.
... An experimental model [10] was used to determine the pharmacokinetics of cefepime in the rat during multiple organ function failure. The pulmonary concentrations were significantly reduced by comparison with the healthy control animals, despite similar plasma concentrations. ...
This review is the fruit of multidisciplinary discussions concerning the continuous administration of beta-lactams, with a special focus on cefepime. Pooling of the analyses and viewpoints of all members of the group, based on a review of the literature on this subject, has made it possible to test the hypothesis concerning the applicability of this method of administering cefepime. Cefepime is a cephalosporin for injection which exhibits a broader spectrum of activity than that of older, third-generation cephalosporins for injection (cefotaxime, ceftriaxone, ceftazidime). The specific activity of cefepime is based on its more rapid penetration (probably due to its zwitterionic structure, this molecule being both positively and negatively charged) through the outer membrane of Gram-negative bacteria, its greater affinity for penicillin-binding proteins, its weak affinity for beta-lactamases, and its stability versus certain beta-lactamases, particularly derepressed cephalosporinases. The stability of cefepime in various solutions intended for parenteral administration has been studied, and the results obtained demonstrated the good compatibility of cefepime with these different solutions. These results thus permit the administration of cefepime in a continuous infusion over a 24-h period, using two consecutive syringes.
... Although these results were obtained by identical means to the measurement of ELF penetration by method A in the present study, they are y25% higher than the present estimates in injured lung using urea, although direct comparison is difficult due to differences in lavage technique, experimental model and timing. Equilibration of CELF,cefepime with plasma cefepime concentrations is compatible with the limited cefepime serum protein-binding of 17% in rat [15] and 12.5-14.5% in dog [16]. In the present study, CELF,cefepime/ plasma cefepime concentration ratios were not different in normal versus injured lung, despite different plasma concentrations. ...
Full-text available
The efficacy of antimicrobial agents against pulmonary infections depends on their local concentrations in the lung. The aims of the present study were to: 1) compare technetium-99m diethylenetriaminepenta-acetic acid (99mTc-DTPA) and urea as markers of epithelial lining fluid (ELF) dilution for measuring ELF concentrations of pharmaceuticals; 2) quantify ELF cefepime concentrations in normal and injured lung; and 3) measure the increase in permeability to cefepime following oleic acid-induced acute lung injury. A modified bronchoalveolar lavage technique, based on equilibration of infused 99mTc-DTPA, was used to measure ELF volume. Cefepime was administered intravenously at steady plasma levels. Six serial bronchoalveolar lavages were performed 5 h after the beginning of infusion. ELF to plasma cefepime concentration ratios were 95 +/- 17 and 100 +/- 14.5% in normal and injured lung respectively. When urea was used as marker, cefepime concentration ratios were underestimated at 16.4 +/- 2.7 and 73.9 +/- 8.4% respectively. Cefepime blood/ airspace clearance increased from 3.8 +/- 0.7 micro x min(-1) in controls to 39.8 +/- 4.9 microL x min(-1) in acute lung injury. It was concluded that: 1) cefepime concentrations in epithelial lining fluid were in equilibrium with those in plasma in both normal and injured lung after 5 h at steady plasma concentrations; 2) epithelial lining fluid cefepime concentration by the urea method was much less underestimated in injured versus normal lung; and 3) acute lung injury induces a 10-fold elevation of cefepime blood/airspace clearance.
Animal models in the PK/PD evaluation of antimicrobial therapy have proven to be a critical element in drug development and dosing refinement for numerous infectious diseases. There are several variables that are taken into consideration when animal models are utilized. These can include host-specific variables such as the animal species, route of infection, infection site, immune status, end organ/tissue sampling and optimal endpoint measure. Pathogen-specific variables include the genus/species, inoculum size, virulence, and drug susceptibility. Finally, therapeutic variables include route of drug administration, timing of therapy, dose level and frequency, metabolism and elimination, and duration of therapy. This list of variables may seem challenging; however, carefully controlled animal model studies are the cornerstone of PK/PD therapeutic evaluations that lead to dosing regimen optimization, limiting drug-related toxicity, guiding therapeutic drug monitoring, and setting of drug susceptibility breakpoints.
To determine the pharmacokinetic parameters of cefpirome, a new so-called fourth-generation cephalosporin, in previously healthy trauma patients with posttraumatic systemic inflammatory response syndrome (SIRS) and to compare them to parameters obtained in matched, healthy volunteers. A prospective study. 12-bed surgical intensive care unit in a university hospital. 9 severe [Injury Severity Score, median (range) 29 (16-50)] trauma patients on mechanical ventilation with proven or suspected cefpirome-susceptible nosocomial infection, with no renal or hepatic failure, and healthy volunteers matched for age (+/- 5 years), sex, and body surface area (+/- 10%) were enrolled. All were men. Cefpirome (2 g twice daily) was continuously infused over a 0.5 h period alone or concomitantly with ciprofloxacin (400 mg over 1 h, twice daily). Antibiotic concentrations in plasma were measured by high-performance liquid chromatography; their pharmacokinetic parameters were evaluated at 12 time points after the first drug administration using a noncompartmental model. Cefpirome pharmacokinetic parameters for the two groups were similar despite a wider variation for trauma patients. Specifically, the median (range) time during which the cefpirome concentration in plasma remained over 4 mg/l (corresponding to the French lower cutoff determining cefpirome susceptibility) was 9.5 (7- > 12) and 9 (8-12) h for trauma patients and healthy volunteers, respectively. In the group of five patients receiving combined antibiotic therapy, the interindividual variability of pharmacokinetics was wider for ciprofloxacin than for cefpirome. No major pharmacokinetic modification was noted when cefpirome was given to trauma patients with posttraumatic SIRS without significant organ failure, indicating that no dosage adjustment seems required in this population. However, larger studies including determination of antibiotic levels in tissues are warranted to confirm these results.
Despite the high rate of therapeutic failures in ventilator-associated pneumonia, up to now there has been no animal model specifically designed for antimicrobial evaluation. A rabbit model of ventilator-associated pneumonia is described for the first time in this study. DESIGN Prospective, randomized experimental study. An animal research laboratory. Male New Zealand healthy rabbits (n = 44). After oral intubation and an hour of mechanical ventilation, animals in the ventilator-associated pneumonia group (n = 22) were infected intrabronchially with a calibrated inoculum of. The nonventilated pneumonia group (n = 22) was composed of animals that received the same inoculum in the absence of mechanical ventilation. Rabbits from both groups were randomly killed 3, 6, 12, 24, or 48 hrs after inoculation. Pneumonia evaluation was based on histologic (macroscopic and microscopic score) and bacteriologic (bacterial count) findings. Infected animals undergoing mechanical ventilation rapidly developed a progressive bilateral and multifocal pneumonia. Lung bacterial mean (sd) concentration was 6.48 (0.71) log10 colony-forming units (cfu) per gram of tissue at the 48th hour, whereas bacteremia occurred in most cases. In the nonventilated pneumonia group, pneumonia was less severe in terms of bacterial count (3.18 [1.86] log10 cfu/g; p <.05), and spleen cultures remained negative. In addition, microscopic examination revealed noninfectious lung injury in the ventilator-associated pneumonia group, especially hyaline membrane filling alveolar spaces. Of note, these features were never observed in the nonventilated pneumonia group. An animal model of ventilator-associated pneumonia was obtained in immunocompetent rabbits. Histopathologic and bacteriologic features were similar to those found in humans. Obviously, pneumonia was more severe when animals underwent mechanical ventilation, especially in terms of systemic spread. Noninfectious lung injury corresponding to ventilation-induced lung injury may explain the difference. This model emphasizes the strong impact of both mechanical ventilation and infection on lung because they seem to act synergistically when causing alveolar damage. Moreover, it seems well suited to testing antimicrobial effectiveness.
Streptococcus pneumoniae is a leading cause of community-acquired pneumonia and is responsible for early-onset ventilator-associated pneumonia as well. In intensive care units, community-acquired pneumonia is still associated with a mortality rate of up to 30%, especially when mechanical ventilation is required. Our objective was to study to what extent MV could influence the efficacy of moxifloxacin in a rabbit model of pneumonia. Prospective experimental study. University hospital laboratory. Male New Zealand White rabbits (n = 75). S. pneumoniae (16089 strain; minimal inhibitory concentration for moxifloxacin = 0.125 mg/L) was instilled intrabronchially. Four hours later, a human-like moxifloxacin treatment was initiated in spontaneously breathing (SB) and mechanically ventilated (MV) animals. Untreated rabbits were used as controls. Survivors were killed 48 hrs later. Pneumonia was assessed and moxifloxacin pharmacokinetics were analyzed. Moxifloxacin treatment was associated with an improvement in survival in the SB animals (13 of 13 [100%] vs. eight of 37 [21.6%] controls). The survival rate was less influenced by treatment in MV rabbits (seven of 15 [46.1%] vs. one of eight [12.5%] controls). The lung bacterial burden was greater in MV compared with SB rabbits (5.1 +/- 2.4 vs. 1.6 +/- 1.4 log10 colony-forming units/g, respectively). Nearly all the untreated animals presented bacteremia as reflected by a positive spleen culture. No bacteremia was found in SB animals treated with moxifloxacin. In contrast, three of 13 (23.1%) moxifloxacin-treated and MV animals had positive spleen cultures. The apparent volume of distribution of moxifloxacin was lower in MV compared with SB rabbits. In our model of moxifloxacin-treated S. pneumoniae pneumonia, mechanical ventilation was associated with a higher mortality rate and seemed to promote bacterial growth as well as systemic spread of the infection. In addition, the volume of distribution of moxifloxacin was reduced in the presence of mechanical ventilation. Although the roles of factors such as anesthesia, paralysis, and endotracheal tube insertion could not be established, these results suggest that mechanical ventilation may impair host lung defense, rendering antibiotic therapy less effective.
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Gentamicin intrapatient pharmacokinetics variations were studied in 40 critically ill medical patients, suffering gram-negative sepsis. These patients were studied in two phases throughout gentamicin treatment: firstly, on the second day of treatment, when aggressive fluid therapy was required, and secondly, five days later, when patients had achieved a more stable clinical condition. Pharmacokinetic parameters were determined using least squares linear regression analysis assuming a one-compartment model using the Sawchuk-Zaske method. The apparent volume of distribution (Vd) in the first phase of the study was 0.43 +/- 0.12 L/kg, while on the seventh day of treatment it was 0.29 +/- 0.17 L/kg (p less than 0.001). Statistically significant differences were also observed for peak serum concentration (p less than 0.001), total dosage recommended (p less than 0.001) and half-life (p less than 0.05), whilst differences were not found for trough levels. From the analysis of the results obtained, we recommend increasing the initial dosage and monitoring plasma levels within the first days of therapy in critically ill patients treated with gentamicin, since important variations in aminoglycoside Vd related to disease, fluid balance and renal function, commonly occur in these patients.
Les aminosides et les β-lactamines sont fréquemment utilisés dans le traitement des infections nosocomiales des malades en ventilation mécanique. La pharmacocinétique de 3 antibiotiques (un aminoside : la tobramycine, et 2 β-lactamines : l'azlocilline et la cefmenoxime) a été étudiée chez ce type de patient. Les résultats mettent en évidence une augmentation importante dans tous les cas du volume de distribution (VD), et sa grande variabilité entre les différents patients. Les modifications du VD, impliquent soit un risque de sous-dosage par “dilution” du médicament dans un VD augmenté lorsque sont utilisées des posologies standard, soit un risque de surdosage, surtout pour les aminosides si les posologies sont trop augmentées afin d'obtenir des taux sériques satisfaisants.
The influence of controlled mechanical ventilation (CMV) on the pharmacokinetic profile of gentamicin has been examined in 23 patients after elective open heart surgery. A parallel design was adopted in two groups of patients; 13 patients requiring CMV for at least 32 h after surgery, all of whom were able to breath spontaneously (SB) after 72 h (study group), and 10 patients who required CMV for only a brief period and who showed SB at 32 h postsurgery. Haemodynamic parameters remained stable throughout the study. Apparent volume of distribution (VZ), half-life (t1/2), total clearance (CL), peak (Cmax") and trough (Cmin") plasma levels at steady-state for target levels (6-8 microgram/ml), were measured. In the study group significant differences between CMV and SB conditions were found in VZ (mean 0.36 and 0.25 l/kg). t1/2 (mean 3.63 and 2.90 h) and Cmax" (mean 4.30 and 5.53 microgram/ml) while Cmin" (mean 1.06 and 0.92 did not change significantly. In contrast, the pharmacokinetics in the control group showed no differences. It appears that CMV leads to an increase in gentamicin Vz which accounts for the fall in Cmax" below the therapeutic dose range (less than 5 microgram/ml) recommended for gentamicin. It seems advisable to use a large dose of gentamicin in patients receiving CMV, even before the level is assessed.
Differences in pharmacokinetic data of aminoglycosides, ceftazidime and ceftriaxone between intensive care patients and volunteers or patients who are less severely ill, are described. Similar differences are observed for midazolam. In severely ill patients with normal renal function a wide interpatient variability of aminoglycoside half-life (t1/2) and increased distribution volume (Vd) are observed. This results in inadequate serum levels. A pharmacokinetic approach of drug dosing, based on serum concentrations in individual patients, is advised. For ceftazidime and ceftriaxone similar changes of t1/2 and Vd are observed. Since protein binding is frequently reduced in severely ill patients, the influence of altered binding of highly bound drugs on Vd and drug clearance is discussed. As both may be increased by reduced protein binding, the change of t1/2 to be expected is unpredictable. Dosing regimens should be based on pharmacokinetic data derived from patients whose severity of disease is comparable to that of the patients to be treated.
We studied prospectively 49 patients being treated in an intensive care unit with aminoglycosides for gram-negative sepsis. Pharmacokinetic data were calculated from three post-dose serum levels using a one-compartment model. Doses required to achieve peak levels between 5 and 10 mg/l with trough levels approximately 1.0 mg/l ranged between 2 and 12 mg/kg per day (mean dose 7 mg/kg per day). During therapy 60% of the patients had a change in their apparent volume of distribution (Vd) of greater than 20%. These patients were likely to have confirmed infection and to be febrile at the start of treatment. Two to three weeks after discharge ten patients were restudied after a single dose of aminoglycoside. There was a reduction in mean Vd from 0.24 to 0.18 l/kg (P less than 0.02). Critically ill patients have significantly larger volumes of distribution and may require larger doses per kilogram of body weight of aminoglycoside to achieve therapeutic concentrations. Due to considerable variation in kinetic parameters, the use of standard doses or dosing nomograms is not recommended.
A high-pressure liquid chromatographic assay was developed for the quantitative analysis of a new cephalosporin, BMY-28142, in plasma and urine. The plasma method involved protein precipitation with acetonitrile and trichloroacetic acid followed by extraction of the acetonitrile into dichloromethane. After centrifugation, the organic phase was discarded, the aqueous solution was injected into a reverse-phase column, and peaks were detected at 280 nm. The urine method involved dilution of a urine sample with sodium acetate buffer (pH 4.25) and direct injection into the high-pressure liquid chromatography system. The assay validation data indicate that the assays for BMY-28142 in plasma and urine were specific, accurate, and reproducible. The analytical methods were applied to the determination of protein binding in human serum and to a pharmacokinetic study in rats. The results of the protein-binding study indicated that BMY-28142 was 16.3% bound to human serum proteins. In the pharmacokinetic study in rats, the maximum level in plasma of 38.7 micrograms/ml was achieved at 2.33 h after administration of a subcutaneous dose of 100 mg/kg. The levels in the plasma then declined with an elimination half-life of about 0.56 h. The mean values for the steady-state volume of distribution and total body clearance were 0.46 liters/kg and 11.9 ml/min per kg, respectively. The 0- to 24-h excretion of intact BMY-28142 in urine accounted for 88.6% of the dose.
The pharmacokinetic disposition of aminoglycosides in critically ill patients with sepsis was studied. In an open-label study of the disposition of gentamicin and tobramycin, individualized pharmacokinetic values of 100 critically ill patients in the surgical intensive-care unit were compared with those of a concurrently monitored group of 100 surgery patients who were not critically ill. The a priori computer-predicted dosage requirements of the critically ill patients were also compared with the dosages derived from their individualized pharmacokinetic values, and intrapatient variation in the critically ill patients was studied. Serum concentration-time data were analyzed using a one-compartment model and the DataMed Clinical Support Services system to provide individualized dosage requirements. Initial dosing guidelines were also generated for the critically ill patients using the a priori model of the DataMed Clinical Support Services program and patient demographic information. The critically ill patients were significantly older, had higher serum creatinine concentrations (SCr), and had lower elimination rate constants (k) and total body clearances (CL) than the surgery patients who were not critically ill. The volume of distribution (V) was not significantly different. The a priori computer predictions for the critically ill patients were significantly lower than the individualized values for V, CL, dose, and amount of drug per 24 hours. The dosing regimen from the a priori model was the same as the individualized regimen in only 2/100 patients. In the 76 critically ill patients who had a second pharmacokinetic analysis performed, there was a significant decrease in k and CL from the first analysis.(ABSTRACT TRUNCATED AT 250 WORDS)