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Antimicrobial Agents and Chemotherapy, January 2002, p. 132-134, Vol. 46, No. 1
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.46.1.132-134.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Division of Infectious Diseases, Departments of Medicine,1 New York College of Osteopathic Medicine Microbiology and Immunodiagnostic Laboratory of the New York Institute of Technology, Old Westbury, New York 11578,2 Pharmacology, New York Medical College, Valhalla, New York 105953
Received 14 May 2001/ Returned for modification 13 August 2001/ Accepted 14 October 2001
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0.4 µg/ml and this agent is also effective clinically (2, 6). While most authoritative sources recommend treatment regimens for patients with Lyme disease similar to that employed for other spirochetal diseases, duration of therapy is nonetheless a topic of controversy (20, 21). The treatment durations recommended in the Infectious Diseases Society of America Practice Guidelines on the Treatment of Lyme Disease range from 14 to 28 days, which is considerably longer than those used successfully to treat patients with infection due to relapsing-fever borrelia (one dose to 10 days of therapy) (4, 19). Unlike most other spirochetal microorganisms, B. burgdorferi can be readily cultured in vitro and a variety of rodents and other laboratory animals are suitable for experimental studies. In animal experiments, 5 to 10 days of treatment of rodents (79) and 30 days of therapy of dogs (14) using the appropriate dosage and type of antibiotic cure the infection on the basis of the inability to recover B. burgdorferi by culture of postmortem tissue samples. Shorter courses of treatment, however, have not been systematically studied.
The purpose of this study was to determine if ceftriaxone therapy of mice could be shortened to a time period estimated to achieve a drug level in serum in excess of the MBC for B. burgdorferi for a time period shorter than that which would follow a single parenteral dose given to humans. The second objective was to determine if immunosuppressive doses of corticosteroids affect the activity of short-course therapy with ceftriaxone in vivo.
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Bacteria and bacterial cultures. A strain of B. burgdorferi designated BL206 was used for these experiments. BL206 was isolated from the blood of a patient who presented with erythema migrans. This organism was maintained by passaging in Barbour-Stoenner-Kelly (BSK) medium and used for the infectivity experiments (see below) after appropriate dilutions were made in BSK medium. The organism had been passaged between five and eight times.
The MIC and MBC of ceftriaxone for BL 206 were determined by a modified microplate dilution assay (13). Triplicate wells contained 5 x 105 B. burgdorferi bacteria in BSK medium with and without diluted ceftriaxone (Roche, Nutley, N.J.). After incubation for 48 h, wells were examined by dark-field microscopy and surviving Borrelia bacteria were enumerated as previously described (12).
Induction of immunosuppression. At intervals designated to coincide with antibiotic treatment (described below), one group of mice was given cortisone acetate (Sigma, St. Louis, Mo.) once daily at a dose of 100 mg/kg of body weight for 5 days. The cortisone acetate was suspended and diluted in sterile saline (Abbott Laboratories, North Chicago, Ill.) and injected subcutaneously in a volume of 0.1 ml. The dosage and treatment regimens used here were similar to those used previously by others (3, 22) to immunocompromise mice during experimental Chlamydia or Legionella infection.
Infectivity experiments. Mice infected with BL206 were treated with (i) ceftriaxone (Roche) over a 5-day period, (ii) ceftriaxone over a 24-h period, or (iii) both cortisone acetate and ceftriaxone for 5 days. Control animals included mice infected with BL 206 that were treated with only sterile saline or cortisone acetate.
Mice were infected by injection with a tuberculin syringe intradermally in the abdominal area with 100,000 B. burgdorferi bacteria in a volume of 0.1 ml of BSK medium. At 14 to 21 days later, the mice were given a single daily dose of either saline, ceftriaxone (50 mg/kg/dose), cortisone acetate (100 mg/kg/dose), or ceftriaxone (50 mg/kg/dose) plus cortisone acetate (100 mg/kg/dose) for 5 days. The saline and ceftriaxone injections were given in a volume of 0.1 ml by the intramuscular route. In a separate experiment, one group of infected mice received the five doses of ceftriaxone (50 mg/kg/dose) over a 24-h period, with each dose given once every 6 h (i.e., at 0, 6, 12, 18, and 24 h). Treatment was initiated at a time point at which infection with BL 206 is known to be widely disseminated in C3H mice on the basis of the results of our prior investigations (17).
Five to 7 days after completion of the saline, ceftriaxone, or cortisone acetate treatment, each mouse was humanely euthanatized and exsanguinated and urinary bladder and ear tissue samples (about 7 by 10 mm) were taken to ascertain the infection status of each of the infected and treated mice (13). Separate extracts of excised urinary bladders and ears (collected aseptically) were prepared by mincing the tissues finely with scissors and forceps and suspending them in a small volume (0.3 to 0.4 ml) of BSK medium. After the heavy tissue particles settled out, each of the extract suspensions was added to separate snap-cap tubes containing 4 ml of BSK medium. Tubes were incubated at 33°C, and the cultures were examined microscopically (by dark-field or phase-contrast microscopy) at 2- and 4-week intervals for the presence of live, motile spirochetes.
Ceftriaxone measurements in mouse plasma and pharmacokinetic analysis. Separate groups of age- and sex-matched C3H mice were evaluated for levels of ceftriaxone in plasma at various times after administration of the 24-h ceftriaxone treatment regimen. Whole blood was collected via the ventral tail vein or by cardiac puncture using a tuberculin syringe and placed into heparinized microcentrifuge tubes at 1, 2, 3, 4, 5, 6, and 7 h after administration of the last of the five intramuscular injections of ceftriaxone. About 0.5 to 0.7 ml of plasma per mouse was transferred to a screw-cap 2.0-ml Micro tube (Sarstedt, Newton, N.C.) after centrifugation of the whole blood at 8,000 x g for 5 min. The nonpooled plasma samples were frozen immediately at -70°C until tested. At least three plasma samples were collected at each time point. Ceftriaxone levels were determined by a high-performance liquid chromatographic procedure (1) done by a commercial laboratory (Department of Laboratories, Barnes-Jewish Hospital, St. Louis, Mo.). The lower limit of detection by the assay was 0.2 µg/ml, and the upper limit was 200 µg/ml. Plasma samples were shipped frozen to the testing laboratory by overnight delivery. The data were analyzed by using an open two-compartment pharmacokinetic model (PK Analyst; Micro Math Scientific Software, Salt Lake City, Utah).
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TABLE 1. Efficacy of ceftriaxone in B. burgdorferi-infected mice treated with and without cortisone acetate
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TABLE 2. Efficacy of five doses of ceftriaxone given over either 24 h or 5 days to C3H mice infected with B. burgdorferi
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) was 29 min. The terminal elimination half-time (t1/2ß) was 200 min.
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FIG. 1. Ceftriaxone levels in the plasma of C3H mice at various time points after administration of the fifth and last dose of ceftriaxone (50 mg/kg given intramuscularly every 6 h). The mean ceftriaxone level and the standard error are plotted for each time point.
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The lack of a detrimental effect of corticosteroid treatment on the success of a 5-day course of therapy was consistent with the findings reported by Kazragis et al. (7), who showed that a 9-day course of ceftriaxone reliably eradicated B. burgdorferi infection in mice with severe combined immunodeficiency (SCID mice).
The every-6-h dosage regimen was evaluated because the t1/2 of ceftriaxone in mice was believed to be
1 h on the basis of several reports (5, 11, 15, 16). Our data, however, suggest that the pharmacokinetics of ceftriaxone in C3H mice may be more complicated than previously believed and are consistent with a two-compartment model in which the t1/2 of the first phase is short (29 min) but in which there is a more prolonged terminal t1/2 of approximately 200 min. Some caution may be warranted in the interpretation of these results since, despite the relatively good fit of the data by least-squares analysis, certain of the individual-animal datum points are close to the sensitivity limit of the analytical method used. Supporting evidence for two-compartment kinetics exists for mice treated with other cephalosporins. In a study by van Ogtrop et al. (15) in which drug concentrations in plasma were measured for a 4-h period after dosing, cefoperazone, ceftazidime, and cefepime showed evidence of two-compartment elimination. Ceftriaxone, also evaluated in the Ogtrop study (15), did not show evidence of two-compartment elimination over the 4-h period, but our data demonstrate that the slower elimination phase could be missed unless datum points are extended beyond 4 h. On the basis of our analysis, administration of five doses of ceftriaxone over a 24-h period should result in levels of ceftriaxone in mouse plasma in excess of the MBC for the B. burgdorferi strain used in this study for just under 60 h, which is a shorter time period than would be expected for intramuscular administration of a single 125-mg dose of ceftriaxone to humans (data not shown). This is attributable to the approximately 7-h t1/2 of ceftriaxone in adult humans (11).
A limitation of this study is that only a single strain of B. burgdorferi was studied and therefore, before generalizing conclusions can be drawn, additional strains should be investigated. In addition, only a single class of antibiotic and only mice with recent B. burgdorferi infection were studied. In prior reports, however, a 5-day course of ceftriaxone eradicated B. burgdorferi infection in C3H mice independently of when the infection occurred and for as long as 90 days after the onset of infection (8).
Extrapolation from studies with laboratory animals to humans should be done with caution. However, it is interesting that Weber et al. (18) successfully treated a group of German patients with erythema migrans with single daily 1-g doses of ceftriaxone administered for just 5 days. Rigorous clinical trials are needed to determine more precisely the appropriate duration of antibiotic therapy for patients with early uncomplicated Lyme disease.
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