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Antimicrobial Agents and Chemotherapy, November 2002, p. 3580-3584, Vol. 46, No. 11
0066-4804/02/$04.00+0 DOI: 10.1128/AAC.46.11.3580-3584.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Departments of Medicine,1 Medical Research, Chi Mei Medical Center,6 Departments of Biochemistry,2 Medicine, National Cheng Kung University Medical College, Tainan,3 Division of Clinical Research, National Health Research Institutes,4 Center for Disease Control, Taipei, Taiwan5
Received 14 March 2002/ Returned for modification 4 June 2002/ Accepted 28 July 2002
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Most of the V. vulnificus isolates are susceptible in vitro to a variety of antibiotics (1, 3, 11, 13, 14; P. R. Hsueh, J. C. Chang, S. C. Chang, S. W. Ho, and W. C. Hsieh, Letter, Eur. J. Clin. Microbiol. Infect. Dis. 14:151-153, 1995). Tetracycline has been recommended as the antimicrobial agent of choice for the treatment of V. vulnificus infection because of the effectiveness of tetracycline for V. cholerae infections. More recently, our in vitro study showed that a combination of cefotaxime and minocycline had a synergistic effect against V. vulnificus (6). A further in vivo study showed that therapy with a combination of cefotaxime and minocycline is more advantageous than single-drug regimens with these agents for the treatment of severe experimental murine V. vulnificus infection (9). Ciprofloxacin has also been used successfully for the treatment of V. vulnificus wound infections (M. C. Meadors and G. A. Pankey, Letter, J. Infect. 20:88-89, 1990). In general, the newer fluoroquinolones developed over the past few years have greater potency, a broader spectrum of antimicrobial activity, greater in vitro efficacy against resistant organisms, and a better safety profile than other antimicrobial agents. Moreover, step-down therapy, a cost-saving alternative, has been claimed to be advantageous. For this reason, the activities of the new fluoroquinolones against V. vulnificus were evaluated in the present study both in vitro and in vivo in comparison with that of cefotaxime-minocycline.
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Determination by time-kill studies of the inhibitory effect of the cefotaxime-minocycline combination and six newer fluoroquinolones on V. vulnificus. Bacterial concentrations were diluted in 125-ml conical glass flasks to around 5.0 x 105 CFU/ml in 25 ml of fresh Mueller-Hinton broth. Cefotaxime, minocycline, and the six newer fluoroquinolones were prepared and placed in flasks at the following concentrations: cefotaxime and minocycline, 0.03 µg/ml each; moxifloxacin, 0.015, 0.03, 0.06, 0.075, 0.09, and 0.12 µg/ml; gatifloxacin, 0.015, 0.03, 0.06, 0.075, 0.09, and 0.12 µg/ml; sparfloxacin, 0.015, 0.03, 0.06, 0.075, 0.09, and 0.12 µg/ml; levofloxacin, 0.075, 0.015, 0.03, 0.06, 0.075, and 0.09 µg/ml; ciprofloxacin, 0.015, 0.03, 0.045, 0.06, 0.075, and 0.09 µg/ml; and lomefloxacin, 0.06, 0.09, 0.12, 0.18, 0.25, and 0.36 µg/ml. Each flask was incubated under the aforementioned conditions. Duplicate samples were removed for determination of CFU at specified time intervals as described previously (6), except that Luria-Bertani agar plates were used and incubated at 37°C overnight. All the experiments were performed at least twice for confirmation of the results.
In vivo efficacies of combined cefotaxime-minocycline treatment and of six newer fluoroquinolones against experimental V. vulnificus infection in mice. The marketed parenteral forms of cefotaxime, minocycline, and ciprofloxacin used in in vivo experiments were provided by Hoechst Taiwan Co., Ltd., Lederle Parenterals, Inc. (Carolina, Puerto Rico), and Bayer AG, respectively. Parenteral forms of moxifloxacin, levofloxacin, gatifloxacin, sparfloxacin, and lomefloxacin were not available in Taiwan, so their standard powders were diluted to the desired concentration for the experiments. Antibiotics were freshly diluted in sterile 0.85% saline on the morning of the day the experiment was conducted and delivered in sterile disposable plastic syringes.
The clinical isolate V. vulnificus VV5823 was used throughout the study. The bacterial inocula were prepared as previously described (9). Five- to six-week-old female inbred BALB/c mice (Animal Center, National Science Council, Taipei, Taiwan) weighing 20 g on average were used throughout the study. An inoculum size of 107 CFU was chosen for the animal experiments because large inoculum size was proven in our previous report to be more discriminatory for evaluation of the efficacy of the treatment regimens (9). In experiment 1, 1.5 x 107 CFU of V. vulnificus was injected subcutaneously at a point over the right thigh of each mouse. There were three groups, including the control, the cefotaxime-minocycline-treated, and the moxifloxacin-treated groups, with 32 mice in each group. Cefotaxime, minocycline, or moxifloxacin was given intraperitoneally in a 0.1-ml volume, beginning 2 h after the animal was infected. The doses of antibiotics were determined according to the recommendations of the pharmaceutical companies. A 30-mg dose of cefotaxime/kg of body weight was given every 6 h, and a loading dose of 4 mg of minocycline/kg followed by a maintenance dose of 2 mg of minocycline/kg was given every 12 h. The dose of moxifloxacin was as follows: a loading dose of 16 mg/kg, followed by a maintenance dose of 8 mg/kg every 24 h. Control animals received 0.1 ml of sterile 0.85% saline every 6 h. Antibiotics were given for a total of 42 h. The numbers of surviving mice were recorded at 6-h intervals beginning after the initial treatment and ending 120 h after treatment began. For humanitarian reasons, animals were euthanized when they were moribund even though they were still breathing. The experimental design of experiment 2 was identical to that of experiment 1 except that inocula of 3.5 x 107 CFU of V. vulnificus VV5853 were used and animals were treated for a total of 36 h. There were seven groups of 15 mice each, including six groups treated with fluoroquinolones and a saline-treated control group. The doses of the newer fluoroquinolones were as follows: for moxifloxacin, levofloxacin, and gatifloxacin, a loading dose of 16 mg/kg of body weight followed by a maintenance dose of 8 mg/kg every 24 h; for sparfloxacin, ciprofloxacin, and lomefloxacin, loading doses of 10, 16, and 8 mg/kg, respectively, followed by maintenance doses of 5, 8, and 4 mg/kg, respectively, every 12 h. The antibiotics were given for a total of 36 h. The animal experiments have complied with all relevant national guidelines of the Republic of China and with the Chi Mei Foundation Medical Center Animal Use Policy.
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Determination of the inhibitory effect of combined cefotaxime-minocycline treatment and of six newer fluoroquinolones on V. vulnificus in time-kill kinetics. When approximately 5 x 105 CFU of V. vulnificus/ml was incubated with gatifloxacin, moxifloxacin, ciprofloxacin, sparfloxacin, and levofloxacin at MICs, the bacterial growth was inhibited during the initial 6, 8, 8, 12, and 36 h, respectively, and thereafter, V. vulnificus regrew (Fig. 1a). When subinhibitory concentrations of cefotaxime (0.03 µg/ml, one-half the MIC) and minocycline (0.03 µg/ml, one-half the MIC) were combined in the same culture, the inhibitory effect on V. vulnificus persisted for more than 48 h with no regrowth noted (Fig. 1b). The same result was observed when the following drugs were used at the concentrations indicated: moxifloxacin, 0.075 µg/ml (five-fourths the MIC) (Fig. 1b); gatifloxacin, 0.06 µg/ml (two times the MIC) (data not shown); sparfloxacin, 0.09 µg/ml (five-fourths the MIC); levofloxacin, 0.045 µg/ml (one and a half times the MIC); ciprofloxacin, 0.06 µg/ml (two times the MIC); and lomefloxacin, 0.12 µg/ml (MIC) (Fig. 1a). The MICs of sparfloxacin, levofloxacin, and lomefloxacin were equivalent to the minimal bactericidal concentrations of these drugs (Fig. 1a).
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FIG. 1. (a) Inhibition of growth curves of V. vulnificus VV5823 (inoculum size, 5 x 105 CFU/ml) after incubation with different fluoroquinolones at MICs. The lower limit of detection was set at 10 colonies (100 CFU/ml). (b) Inhibition of growth curves of V. vulnificus VV5823 (inoculum, 5 x 105 CFU/ml) after incubation with minocycline, cefotaxime alone, a combination of cefotaxime and minocycline, or different concentrations of moxifloxacin. MICs of cefotaxime, minocycline, and moxifloxacin were 0.06 µg/ml.
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FIG. 2. (a) Survival rates of mice (n = 15) subcutaneously injected with 1.5 x 107 CFU of V. vulnificus following treatment with a cefotaxime-minocycline combination, moxifloxacin, or saline. The differences between moxifloxacin- and saline-treated groups and between cefotaxime-minocycline-treated and saline-treated groups were significant (P < 0.001) by log rank test, while that between cefotaxime-minocycline-treated and moxifloxacin-treated groups was not significant. (b) With an inoculum of 3.5 x 10 7 CFU and antibiotic treatment for 36 rather than 42 h, survival rates among mice (n = 15) treated with the fluoroquinolones were significantly higher than that of the saline-treated control group (P < 0.01, log rank test) but not significantly different from one another.
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Because of the sporadic occurrence of V. vulnificus infections, there are virtually no randomized clinical trials to determine which antibiotic is most effective for treatment. Morris and Tenney (20; J. G. Morris, Jr., and J. Tenney, Letter, JAMA 253:1121-1122, 1985) stressed the superiority of tetracycline over cefotaxime based on the study of a mouse model conducted by Bowdre et al. (3). Fang (F. C. Fang, Letter, Clin. Infect. Dis. 15:1071-1072, 1992) advocated the use of tetracycline to treat V. vulnificus infections because an antibiotic which inhibits protein synthesis was thought to be preferable to one which damages the cell wall and may cause the release of an increased level of toxic microbial proteins. On the other hand, other reports of clinical experiences suggest that the expanded-spectrum cephalosporins may be superior to tetracycline for treating V. vulnificus infections (5; Chuang, letter). A previous in vitro study showed the synergistic effect of cefotaxime and minocycline against V. vulnificus (6). A further in vivo study showed that therapy with a combination of cefotaxime and minocycline was more efficacious than single-drug therapy with these antibiotics for the treatment of severe experimental murine V. vulnificus infection (9).
The mouse model of V. vulnificus infection used in the present study was previously shown to cause necrotizing fasciitis, bacteremia, and death within 24 h, mimicking V. vulnificus bacteremia in humans (7). V. vulnificus can produce mutiple extracellular cytolytic or cytotoxic toxins and enzymes that are associated with extensive tissue damage and may play a major role in the development of sepsis (7, 8, 12, 17, 19, 23). More than 50% of cases of V. vulnificus infections lead to either primary or secondary severe soft tissue involvement manifesting as hemorrhagic bullae or necrotizing fasciitis (5, 16). The clinical course of V. vulnificus infection in a septicemic patient is fulminant, and over 50% of such patients die within 48 h of hospitalization (5, 16). The skin manifestations usually develop at the time of admission or within 24 h of hospitalization. This condition can worsen rapidly, within hours (5). In the case of severe wound infection, especially in necrotizing fasciitis, widespread obliterative vasculitis and vascular necrosis are the major features of the skin lesion and can seriously compromise the blood supply. An antibiotic with good tissue penetration ability is urgently needed in these clinical situations. Müller et al. showed that moxifloxacin was promising in the treatment of skin and soft tissue infections (21). This is because the drug concentrations attained in the fluid in the interstitial spaces in humans and in skin blisters following a single dose of 400 mg exceeded the MIC90s for most clinical isolates (22). The unique site of action and the good tissue penetration abilities of the newer fluoroquinolones may be related to their efficacy in clinical use. In view of the difference in pharmacokinetic parameters between mice and humans, the question of whether or not all the results of animal model studies can be extrapolated in clinical situations has yet to be answered.
Taken together and in comparison to a combination of cefotaxime and minocycline, the newer fluoroquinolones, such as levofloxacin, are potentially useful as monotherapy for severe V. vulnificus soft tissue infections. Further clinical trials with these agents in treating human V. vulnificus infections are warranted.
This work was partly supported by grants (DOH-91-DC-1015, CMFHR 9116) from the Center for Disease Control, the Department of Health, and Chi Mei Medical Center, Tainan, Taiwan, Republic of China.
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