1 School of Pharmacy, University of Connecticut, Storrs, CT 06269; 2 Center for Anti-Infective Research and Development, and 3 Division of Infectious Diseases, Hartford Hospital, Hartford, CT 06102; 4 School of Medicine, Creighton University, Omaha, NE 68178, USA
Received 8 July 2003; returned 15 September 2003; revised 21 October 2003; accepted 5 November 2003
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Abstract |
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Methods: Two sterilized golf Wiffle balls were surgically implanted in the rabbit dorsal cervical area. After 4 weeks, Wiffle balls had filled with tissue cage fluid (TCF), in which 2 mL of 106 cfu/mL of the test isolate were inoculated. To achieve the same T > MIC as in humans, 400 mg/kg of the ß-lactams alone and in combination was administered twice a day via subcutaneous injection. The dosing regimens were as follows: piperacillin alone, 4 g piperacillin/0.5 g tazobactam; ticarcillin alone, 3 g ticarcillin/0.1 g clavulanate; and 3 g ticarcillin/ 0.3 g clavulanate.
Results: The changes in bacterial counts (log cfu/mL) after the 3 day treatments were as follows: 1.03 ± 0.97 (control), 1.31 ± 0.61 (piperacillin), 2.81 ± 0.53 (4 g piperacillin/0.5 g tazobactam), 1.61 ± 0.68 (ticarcillin), 3.42 ± 0.75 (3 g ticarcillin/0.1 g clavulanate) and 1.65 ± 1.47 log cfu/mL (3 g ticarcillin/0.3 g clavulanate). AmpC induction by high-dose clavulanate was observed in rabbit TCF, and was confirmed by the in vitro induction study.
Conclusions: The study indicated that tazobactam significantly enhanced the antibacterial activity of piperacillin against iAmpC P. aeruginosa; clavulanate had synergy with the antibacterial activity of ticarcillin at low concentration, but had no effect on ticarcillin at high concentration due to AmpC induction by clavulanate.
Keywords: piperacillin, tazobactam, ticarcillin, clavulanate, ß-lactamase inhibitor, tissue cage model, ß-lactamase induction
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Introduction |
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Interestingly, clavulanate, a ß-lactamase inhibitor, can induce AmpC ß-lactamase in vitro in clinical isolates of Pseudomonas aeruginosa, Enterobacter cloacae, Serratia marcescens and Citrobacter freundii.13 Clavulanate has synergy with the antibacterial activity of ß-lactams by competing for ß-lactamase and hence protecting ß-lactams from attack. Clavulanate also antagonizes the antibacterial activity of ß-lactams by inducing ß-lactamase production. The enzyme-inducing capacity of clavulanate is concentration dependent.4 In one in vitro study, clavulanate at 2 or 4 mg/L had neither an antagonistic nor a synergic antimicrobial effect in combination with ticarcillin against P. aeruginosa possessing an inducible ß-lactamase.5 Antagonism of ticarcillin by clavulanate was observed when MICs of ticarcillin increased in the presence of 132 mg/L clavulanate.6 In an in vitro pharmacokinetic model, antagonisms of ticarcillin against P. aeruginosa with inducible ß-lactamase were observed in some tests with regimens simulating the clinically relevant concentrations achieved with a 3.1 g dose of ticarcillin/clavulanate (3 g ticarcillin plus 0.1 g clavulanate), and in all tests with regimens simulating clinically relevant concentrations achieved by a 3.2 g dose of ticarcillin/clavulanate (3 g ticarcillin plus 0.2 g clavulanate). No enzyme induction by tazobactam was observed. Moreover, tazobactam enhanced the activity of piperacillin against all tested strains of P. aeruginosa, despite ß-lactamase inducibility of the organism in this in vitro model.7
Although ß-lactamase induction by clavulanate and the resultant antagonism of ticarcillin and other ß-lactams have been extensively studied in vitro, there are insufficient in vivo data available on enzyme induction by clavulanate. It remains unclear whether ß-lactamases could be induced by clavulanate in vivo, with the consequential antagonism of ticarcillin activity. One study in mice showed that clavulanate did not antagonize the efficacy of ticarcillin against ß-lactamase-inducible stains of P. aeruginosa, E. cloacae, C. freundii or S. marcescens,8 but no drug concentration data were presented in this study. As stated above, the ß-lactamase induction level depends on the clavulanate level.
The current study was designed to investigate over a 3 day treatment period the in vivo antimicrobial activities of ß-lactams alone and in combination with ß-lactamase inhibitors against P. aeruginosa possessing an inducible AmpC (iAmpC) ß-lactamase. To understand the impact of ß-lactamase inhibitors on the antimicrobial activities of ß-lactams against this organism, AmpC ß-lactamase induction was studied in vitro and in vivo.
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Materials and methods |
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One clinical bacterial strain of P. aeruginosa, PSA246, which has been shown to possess iAmpC expression in vitro after exposure to clavulanate,7 was used in this study. The stock strain was frozen at 80°C in skimmed milk. Before each experiment the stock bacteria were subcultured twice onto a trypticase soy agar plate with 5% sheeps blood (Becton Dickinson Microbiology Systems, Cockeysville, MD, USA) and incubated at 35°C overnight to ensure bacterium purity. Piperacillin/tazobactam and ticarcillin/clavulanate analytical grade standards for the in vitro test and HPLC assay were obtained from Wyeth Laboratories (Pearl River, NY, USA) and GlaxoSmithKline, respectively. For all in vivo studies, commercially available intravenous preparations of 4 g piperacillin (Pipracil; Lederle Piperacillin, Carolina, Puerto Rico), 4 g piperacillin/0.5 g tazobactam (Zosyn; Lederle Piperacillin), 3 g ticarcillin (Ticar; SmithKline Beecham Pharmaceuticals, Philadelphia, PA, USA) and 3 g ticarcillin/0.1 g clavulanate (Timentin; SmithKline Beecham Pharmaceuticals) were purchased from their respective manufacturers. In addition to the commercial products, the combination of 3 g ticarcillin and 0.3 g clavulanate was used for this study, which was made by adding 0.2 g clavulanate analytical standard to one vial of 3 g ticarcillin/0.1 g clavulanate.
In vitro susceptibility testing
MICs of piperacillin, piperacillin/tazobactam, ticarcillin and ticarcillin/clavulanate for P. aeruginosa PSA246 and a reference strain of P. aeruginosa (ATCC 27853) were determined in duplicate using the broth microdilution method with cation-supplemented MuellerHinton broth and a bacterial inoculum of 5 x 105 cfu/mL, according to NCCLS guidelines.9
Rabbit tissue cage model
This study was approved by the Institutional Animal Care and Use Committee (IACUC) of Hartford Hospital, Hartford, CT, USA. Female New Zealand white rabbits, weighing 4 kg, were used in the present study. All animals received water and food ad libitum. The animal vendor (Covance Research Products, Denver, PA, USA) implanted the golf Wiffle balls in the animals. Wiffle balls are 2 mm thick, 4 cm diameter hollow plastic balls with an even distribution of 26 0.5 cm diameter holes. The procedure for placing the Wiffle balls into the animals was as follows: rabbits were anaesthetized, and two sterilized Wiffle balls were implanted subcutaneously on the rabbit dorsal cervical surface and tacked down on the dorsal musculature with a loosely tied suture of 3-0 Nylon. The skin incision was closed in two layers with absorbable sutures. During the 4 week surgical recovery period, including a 1 week quarantine at the Hartford Hospital Animal Laboratory, the Wiffle balls filled with fluid, the so-called tissue cage fluid (TCF). This fluid served as a bacterial growth medium.10
Antibiotic assay
HPLC methods were developed and validated to determine simultaneously the piperacillin/tazobactam (C. Li, D. Xuan, M. Ye, D. P. Nicolau and C. H. Nightingale, unpublished results) and ticarcillin/clavulanate concentrations,11 respectively, in rabbit serum and TCF. The concentration ranges of the standard curves were 1100 mg/L for piperacillin, tazobactam and ticarcillin, and 0.22 mg/L for clavulanate in rabbit serum and TCF. The relative standard deviations and relative errors of the inter- and intra-assay of these four HPLC methods were <7.3%. Samples containing concentrations above the quantification limits were diluted with tested drug-free rabbit serum or TCF.
Pharmacokinetic/pharmacodynamic study
ß-Lactams are time-dependent antibiotics, i.e. their bacterial killing efficacies are associated with the time for which drug concentrations exceed the MIC. To achieve a similar time above the MIC (T > MIC) in rabbits as in humans for piperacillin (Pipracil, 4 g every 6 h), piperacillin/tazobactam (Zosyn, 4.5 g every 6 h), ticarcillin (Ticar, 3 g every 6 h) and ticarcillin/clavulanate (Timentin, 3.1 g every 6 h), the dose regimens were as follows: 400 mg/kg piperacillin alone or in combination with tazobactam (4 g piperacillin/0.5 g tazobactam), and 400 mg/kg ticarcillin alone or in combination with clavulanate (3 g ticarcillin/0.1 g clavulanate). In addition, to achieve a similar peak concentration of clavulanate in rabbit TCF as in human serum for another clinically used combination of 3 g ticarcillin/0.2 g clavulanate (Timentin, 3.2 g, every 6 h), the dose regimen of 400 mg/kg ticarcillin in the combination of 3 g ticarcillin/ 0.3 g clavulanate was also applied in this study. After sample size analysis, six rabbits for each dose regimen were used, creating a total of six groups, including one control group that did not receive any treatment. Before infection, the rabbit TCF in each Wiffle ball was sampled to test whether it was sterile, then rabbits that had been implanted with Wiffle balls for 4 weeks were infected by percutaneous injection of 2 mL of PSA246 (106 cfu/mL) into each Wiffle ball. After 24 h of organism incubation in the Wiffle balls, the rabbits received antibiotic treatment for 3 days by subcutaneous injection twice a day.
Blood (1 mL) was collected using the marginal ear vein bleeding technique. The sampling time points were as follows: 0 h (prior to dose), and 0.25, 0.5, 1, 2, 4, 6, 8 and 12 h after the first dose. Blood samples were centrifuged, separated and frozen at 80°C until analysis. The bacterial density within the two Wiffle balls of each rabbit was monitored over the 72 h treatment period by aspirating TCF (400 µL) from each Wiffle ball. The sampling time points were as follows: 0 h (prior to the initiation of antimicrobial therapy), and 2, 4, 6, 8, 12, 24, 36, 48, 60 and 72 h after the initiation of therapy. A 10-fold dilution series in saline was made using 100 µL TCF from each Wiffle ball, and a 10 µL sample of each dilution was placed on blood agar plates, followed by incubation for 24 h. To determine the concentration profiles of the antibiotics in TCF during the first dosing interval, TCF samples from one Wiffle ball were stored at 80°C until analysis.
Induction of ß-lactamase
It is important to elucidate the mechanism of the impact of clavulanate on the antimicrobial activity of ticarcillin in vivo, and to confirm that the antagonism in vivo and in vitro arise for the same reason: AmpC ß-lactamase induction. For comparative purposes, tazobactam was also used to test ß-lactamase-induction capacity. An HPLC method was developed (see below) to measure AmpC ß-lactamase activity, and applied to monitor changes in AmpC ß-lactamase activity in the rabbit TCF during the first dosing interval.
In vitro induction
PSA246 was subcultured onto a blood agar plate and incubated at 35°C overnight; five colonies were inoculated into 5 mL of cation-adjusted MuellerHinton broth at 35°C. After a 2 h incubation, tazobactam or clavulanate was added. The final concentrations were as follows: tazobactam 15 mg/L, clavulanate 5 and 15 mg/L. The bacterial density in the broth was assessed over a 12 h induction period. At the same time, 200 µL of the broth was sampled, centrifuged at 5000g for 20 min at 4°C, and the supernatant discarded. The sample was washed once with phosphate buffer (0.1 M, pH 7) and frozen at 80°C. The sampling time points were as follows: 0 h (prior to the induction), and 2, 4, 6, 8 and 12 h after addition of ß-lactamase inhibitors. All experiments were carried out in triplicate.
Sample preparation for enzyme induction tests in vivo
After sampling TCF during the first dose interval as described above, crude ß-lactamase extracts were prepared as follows: a 200 µL TCF sample from one Wiffle ball was centrifuged at 5000g for 20 min at 4°C, and the supernatant discarded. The sample was washed once with phosphate buffer (0.1 M, pH 7) and frozen at 80°C.
Analysis of ß-lactamase activity
After thawing at room temperature, the sample was resuspended in 100 µL phosphate buffer (0.1 M, pH 7), and lysed by 15 cycles of 15 s sonication (Bransonic Ultrasonic, Model 3210; Bransonic, Danbury, CT) at 15 s intervals. During the sonication, samples were maintained in an ice-water bath to protect the enzyme activity from damage by heat. The sonicates were mixed with 100 µL of a 500 mg/L solution of cefalothin, which serves as the hydrolysis substrate. After 530 min incubation at 37°C, the enzyme reaction was terminated by heating in a boiling water bath for 30 s. The precipitated proteins were removed by centrifugation at 10 000g for 20 min. The supernatant was injected directly onto an HPLC system to analyse the residual substrate. The assay was carried out with a Phenomenex Prodigy ODS (3) column (10 µm, 240 x 4.6 mm) (Phenomenex, Torrance, CA, USA), coupled with µBondapak C18 Guard-Pak pre-column (Waters, Milford, MA, USA). The column was maintained at room temperature; the mobile phase consisted of 40:60 (v/v) acetonitrile/phosphate buffer (0.014 M, pH 2.4). The flow rate of the mobile phase was 1 mL/min, and the eluate was monitored at 254 nm. This external standard method was validated before running unknown samples. ß-Lactamase activity in PSA246 after induction in vitro and in vivo was evaluated by assessing the enzymatic reaction rate constant, which is the reaction rate constant of cefalothin at the initial concentration of 250 mg/L degraded by ß-lactamase at 37°C.
Data analysis
Non-compartmental analysis (WinNonlin, version 3.3; Pharsight Corporation, Mountain View, CA, USA) was used to evaluate the concentration profiles of antibiotics in rabbit serum and TCF during the first dose interval. The following parameters were estimated: the maximum concentration (Cmax), the time to reach the maximum concentration (Tmax), the area under the concentrationtime curve (AUC0) and the mean residence time (MRT). Bacterial density changetime curves were plotted for each dosing regimen.
In the ß-lactamase induction study, enzymatic activity was estimated as the enzyme reaction rate constant. The substrate degradation at enzyme reaction follows first-order kinetics. When the natural logarithm of the residual substrate concentration is plotted against time, the slopes of these lines are equal to the rate constant of the enzyme reaction (units: mg/L/min), designated the apparent ß-lactamase activity. Owing to different bacterial densities at different time points, the ß-lactamase activity ratio was used to estimate the enzyme activity change, which was calculated by Equation 1:
Equation 1
Students t-test was used to determine whether there was a statistical difference in the pharmacokinetic parameters between piperacillin in combination with tazobactam, and piperacillin alone. A one-way ANOVA was employed to test for a statistical difference in the pharmacokinetic parameters of ticarcillin among the three different dose regimens. For the pharmacodynamic study, a one-way ANOVA was employed to determine whether there was a statistical difference in bacterial killing between the control group and the ß-lactam alone or in combination with ß-lactamase inhibitor groups. For the enzyme induction study, a one-way ANOVA was used to determine whether there was a statistical difference between these groups in vitro. P values <0.05 were considered statistically significant (S-Plus 2000; Mathsoft, Inc., Seattle, WA, USA).
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Results |
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MICs of piperacillin, piperacillin/tazobactam, ticarcillin and ticarcillin/clavulanate for PSA246 were 16, 8/4, 32 and 32/2 mg/L, respectively. The MICs of all antibiotics and their combinations were <64 mg/L, i.e. PSA246 was susceptible to these two ß-lactams and their combinations.
Antibiotic concentration profiles in rabbit serum and TCF
Figures 14 show the concentrationtime profiles of piperacillin alone, 4 g piperacillin/0.5 g tazobactam, ticarcillin alone, 3 g ticarcillin/0.1 g clavulanate and 3 g ticarcillin/0.3 g clavulanate in rabbit serum and TCF. The mean pharmacokinetic parameters are summarized in Table 1. There was no statistical difference in the pharmacokinetic parameters of piperacillin with or without tazobactam, or ticarcillin with and without clavulanate, in either serum or TCF. These data suggest that tazobactam and clavulanate do not alter the absorption and disposition of piperacillin and ticarcillin in rabbits.
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The antimicrobial activities of these five dose regimens were evaluated by assessing the bacterial density change within the Wiffle ball during the 3 day treatment period. After 24 h incubation in rabbit TCF, the recovery of PSA246 was 5 x 105 cfu/mL immediately prior to antibiotic treatment. All of the bacterial timekill curves are shown in Figures 5 and 6. For the untreated control group, log bacterial density in TCF increased 1.03 ± 0.97 cfu/mL (mean ± S.D., n = 12) after 72 h. For the treatment groups, log changes of the bacterial density in rabbit TCF after 3 days of therapy were as follows (mean ± S.D.): 1.31 ± 0.61 cfu/mL (n = 12) for piperacillin alone group; 2.81 ± 0.53 cfu/mL for the combination 4 g piperacillin/ 0.5 g tazobactam; 1.60 ± 0.63 cfu/mL for ticarcillin alone; 3.42 ± 0.75 cfu/mL for the combination 3 g ticarcillin/0.1 g clavulanate; and 1.65 ± 1.47 cfu/mL for the combination 3 g ticarcillin/ 0.3 g clavulanate.
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ß-Lactamase induction
The in vitro enzyme induction by ß-lactamase inhibitors was conducted in MuellerHinton broth at 37°C. Bacteria grew from 1.26 x 107 to 7.08 x 108 cfu/mL during the 12 h period, and there was no difference in bacterial growth between the four groups. Figure 7 shows the kinetics profiles of ß-lactamase activity versus time. ß-Lactamase in PSA246 remained at a low level in the blank MuellerHinton broth and piperacillin at 15 mg/L during the 12 h incubation, and there was no statistically significant difference between these two groups. However, compared with the enzyme level in the control group at 8 h, ß-lactamase activity increased 38- and 200-fold at clavulanate concentrations of 5 and 15 mg/L, respectively. The data indicate that the higher concentration of clavulanate resulted in increased enzyme induction.
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Discussion |
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The results of this pharmacodynamic study of ticarcillin and clavulanate in immunocompetent rabbits were complicated. Comparing bacterial killing by ticarcillin alone, 0.1 g clavulanate in combination with 3 g ticarcillin enhanced the antimicrobial activity of ticarcillin against this strain of iAmpC P. aeruginosa, but 0.3 g clavulanate in combination with 3 g ticarcillin had no effect on the antimicrobial activity of ticarcillin against the same bacterial strain. Based on the enzyme induction data, we postulated that at the dose of 0.3 g clavulanate, the effect of clavulanate as a ß-lactamase inhibitor balanced the AmpC induced by clavulanate, and that clavulanate mainly acted as a ß-lactamase inhibitor at 0.1 g dose. This may explain why there was no influence of high-dose clavulanate on the antimicrobial activity of ticarcillin, and why there was a synergy of low-dose clavulanate with ticarcillin. To some extent, the observed bacterial killing by ticarcillin in combination with clavulanate in the immunocompetent rabbit contradicts the antagonism of clavulanate to ticarcillin in vitro reported in the study by Lister et al.7 Such contradiction was probably due to the host defences of the immunocompetent animals tested in this study.
Overall, the antimicrobial efficacy data indicated that piperacillin/tazobactam had some advantages over ticarcillin/clavulanate against this strain of P. aeruginosa with its iAmpC. As a ß-lactamase inhibitor, tazobactam inactivated ß-lactamases and potentiated piperacillin against this bacterium. Since the concentration range of tazobactam in human skin, appendix and intestinal mucosa was 6.314.5 mg/L after a single dose of 4 g piperacillin/0.5 g tazobactam via intravenous infusion over 30 min,12 it may be clinically significant that the synergy of piperacillin by tazobactam was observed in rabbit TCF.
The most noteworthy observation of this study was that clavulanate could induce AmpC ß-lactamases in P. aeruginosa in animals, and that the AmpC induction level was related to clavulanate concentrations. As an enzyme inducer, clavulanate induced AmpC ß-lactamase production and failed to enhance the activity of ticarcillin against the tested strain of iAmpC P. aeruginosa. In clinical settings, the ß-lactamase-inducing capacity of clavulanate needs to be defined at clinically relevant concentrations. Clavulanate is well distributed in human tissues, and ticarcillin does not affect the distribution of clavulanate to body tissue or vice versa.13 Clavulanate concentrations reached 17.8 and 32.5 µg/mg in human spongiosa and corticalis bone, respectively, 4585 min after prophylactic administration of 5 g ticarcillin/0.2 g clavulanate.14 Another human study showed that the concentration of clavulanate in the thread fluid was similar to the corresponding serum values, and the concentrations of clavulanate in the blister fluid and lymph were higher than those in serum 1 h after dosing.15 Emergence of resistant P. aeruginosa isolates has been reported in several clinical trials during therapy with ticarcillin/clavulanate combinations, including cases of clinical treatment failure,1618 but no detailed information on AmpC ß-lactamase induction were presented. Further clinical research on combinations of ticarcillin/clavulanate is needed to fully answer this question. The pharmacodynamic results of the combinations of ticarcillin/clavulanate in this study suggest that there is some risk of clavulanate antagonizing ticarcillin when used against P. aeruginosa strains with an inducible ß-lactamase.
In conclusion, there is synergy between tazobactam and piperacillin, as tazobactam enhanced the antimicrobial activity of piperacillin against this strain of iAmpC P. aeruginosa. At low concentrations, clavulanate increased the antimicrobial activity of ticarcillin against this strain of iAmpC P. aeruginosa, but had no effect on the antimicrobial activity of ticarcillin at high concentrations. Moreover, an increase in ß-lactamase activity in this iAmpC strain of P. aeruginosa caused by clavulanate at high concentration was observed in rabbits. One should be cautious when treating serious P. aeruginosa infections with high-dose clavulanate-containing regimens.
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Acknowledgements |
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Footnotes |
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References |
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2 . Moosdeen, F., Keeble, J. & Williams, J. D. (1986). Induction/inhibition of chromosomal beta-lactamases by beta-lactamase inhibitors. Reviews of Infectious Diseases 8, Suppl. 5, S5628.[ISI][Medline]
3 . Weber, D. A. & Sanders, C. C. (1990). Diverse potential of beta-lactamase inhibitors to induce class I enzymes. Antimicrobial Agents and Chemotherapy 34, 1568.[ISI][Medline]
4 . Stobberingh, E. E. (1988). Induction of chromosomal ß-lactamases by different concentrations of clavulanic acid in combination with ticarcillin. Journal of Antimicrobial Chemotherapy 21, 916.[Abstract]
5 . Tausk, F. & Stratton, C. W. (1986). Effect of clavulanic acid on the activity of ticarcillin against Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 30, 5849.[ISI][Medline]
6 . Livermore, D. M., Akova, M., Wu, P. J. et al. (1989). Clavulanate and ß-lactamase induction. Journal of Antimicrobial Chemotherapy 24, Suppl. B, 2333.[Abstract]
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.
Lister, P. D., Gardner, V. M. & Sanders, C. C. (1999). Clavulanate induces expression of the Pseudomonas aeruginosa AmpC cephalosporinase at physiologically relevant concentrations and antagonizes the antibacterial activity of ticarcillin. Antimicrobial Agents and Chemotherapy 43, 8829.
8 . Cavalieri, S. J., Sanders, C. C. & New, C. (1991). Influence of beta-lactamase inhibitors on the potency of their companion drug with organisms possessing class I enzymes. Antimicrobial Agents and Chemotherapy 35, 13437.[ISI][Medline]
9 . National Committee for Clinical Laboratory Standards. (2000). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow AerobicallyFifth Edition: Approved Standard M7-A5. NCCLS, Villanova, PA, USA.
10
.
Xuan, D., Zhong, M., Mattoes, H. et al. (2001). Streptococcus pneumoniae response to repeated moxifloxacin or levofloxacin exposure in a rabbit tissue cage model. Antimicrobial Agents and Chemotherapy 45, 7949.
11 . Li, C., Geng, Q., Nicolau, D. P. et al. (2003). Simultaneous determination of ticarcillin and clavulanate in rabbit serum and tissue cage fluid (TCF) by HPLC. Journal of Chromatography B Analytical Technologies in the Biomedical and Life Sciences 792, 22736.
12 . Sorgel, F. & Kinzig, M. (1994). Pharmacokinetics and tissue penetration of piperacillin/tazobactam with particular reference to its potential in abdominal and soft tissue infections. European Journal of Surgery Supplement 573, 3944.[Medline]
13 . Bush, L. M. & Johnson, C. C. (2000). Ureidopenicillins and beta-lactam/beta-lactamase inhibitor combinations. Infectious Disease Clinics of North America 14, 40933, ix.
14 . Adam, D., Heilmann, H. D. & Weismeier, K. (1987). Concentrations of ticarcillin and clavulanic acid in human bone after prophylactic administration of 5.2 g of timentin. Antimicrobial Agents and Chemotherapy 31, 9359.[ISI][Medline]
15 . Walstad, R. A., Hellum, K. B., Thurmann-Nielsen, E. et al. (1986). Pharmacokinetics and tissue penetration of Timentin: a simultaneous study of serum, urine, lymph, suction blister and subcutaneous thread fluid. Journal of Antimicrobial Chemotherapy 17, Suppl. C, 7180.[ISI][Medline]
16 . File, T. M., Jr, Tan, J. S., Salstrom, S. J. et al. (1984). Timentin versus piperacillin or moxalactam in the therapy of acute bacterial infections. Antimicrobial Agents and Chemotherapy 26, 3103.[ISI][Medline]
17 . Johnson, C. C., Reinhardt, J. F., Wallace, S. L. et al. (1985). Safety and efficacy of ticarcillin plus clavulanic acid in the treatment of infections of soft tissue, bone, and joint. American Journal of Medicine 79, Suppl. 5B, 13640.[ISI][Medline]
18 . Williams, M. E., Harman, C., Scheld, M. et al. (1985). A controlled study of ticarcillin plus clavulanic acid versus piperacillin as empiric therapy for fever in the immunocompromised host. American Journal of Medicine 79, Suppl. 5B, 6772.
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