Course of murine tuberculosis and response to first-line therapy depends on route of infection and inoculum size.

BACKGROUND: In the search for new anti-tuberculosis drugs, numerous potential drugs are being screened in vitro. In animal models, promising new anti-tuberculosis drugs are assessed in terms of toxic side effects and comparative therapeutic efficacy. Mice are frequently used and experimental infections are established in different ways. OBJECTIVE: To investigate to what extent the route of Mycobacterium tuberculosis inoculation is a determinant in the pathogenesis of tuberculosis (TB) and the therapeutic outcome. Results will contribute to insight into the translational value of TB models used for preclinical studies. DESIGN: TB in mice was established through intratracheal or intravenous mycobacterial inoculation. The efficacy of a 26-week treatment regimen was evaluated, including assessment of relapse of infection 13 weeks post-treatment. RESULTS: It was shown that the course of TB and the therapeutic response, in terms of histopathological characteristics and mycobacterial load, in lungs and extra- pulmonary organs is substantially different and dependent on the route of infection applied and the inoculum size used. CONCLUSION: When evaluating the comparative therapeutic potential of novel anti-tuberculosis drugs or drug treatment schedules investigated in different studies, it should be noted that the route of infection applied and the inoculum size used influence the course of murine TB and the therapeutic response to the standard first- line anti-tuberculosis drug regimen.

Improved efficacy of ciprofloxacin administered in polyethylene glycol-coated liposomes for treatment of Klebsiella pneumoniae pneumonia in rats.

Animal and clinical data show that high ratios of the area under the concentration-time curve and the peak concentration in blood to the MIC of fluoroquinolones for a given pathogen are associated with a favorable outcome. The present study investigated whether improvement of the therapeutic potential of ciprofloxacin could be achieved by encapsulation in polyethylene glycol (PEG)-coated long-circulating sustained-release liposomes. In a rat model of unilateral Klebsiella pneumoniae pneumonia (MIC = 0.1 microg/ml), antibiotic was administered at 12- or 24-h intervals at twofold-increasing doses. A treatment period of 3 days was started 24 h after inoculation of the left lung, when the bacterial count had increased 1,000-fold and some rats had positive blood cultures. The infection was fatal within 5 days in untreated rats. Administration of ciprofloxacin in the liposomal form resulted in delayed ciprofloxacin clearance and increased and prolonged ciprofloxacin concentrations in blood and tissues. The ED(50) (dosage that results in 50% survival) of liposomal ciprofloxacin was 3.3 mg/kg of body weight/day given once daily, and that of free ciprofloxacin was 18.9 mg/kg/day once daily or 5.1 mg/kg/day twice daily. The ED(90) of liposomal ciprofloxacin was 15.0 mg/kg/day once daily compared with 36.0 mg/kg/day twice daily for free ciprofloxacin; 90% survival could not be achieved with free ciprofloxacin given once daily. In summary, the therapeutic efficacy of liposomal ciprofloxacin was superior to that of ciprofloxacin in the free form. PEG-coated liposomal ciprofloxacin was well tolerated in relatively high doses, permitting once daily administration with relatively low ciprofloxacin clearance and without compromising therapeutic efficacy.

Efficacies of amphotericin B-desoxycholate (Fungizone), liposomal amphotericin B (AmBisome) and fluconazole in the treatment of systemic candidosis in immunocompetent and leucopenic mice.

The in-vitro activities of amphotericin B-desoxycholate (AmB-DOC), liposomal amphotericin B (L-AmB) and fluconazole were determined against a single strain of Candida albicans. In addition, the efficacies of these agents in the treatment of systematic candidosis in both immunocompetent and leucopenic mice were compared. The minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) of AmB-DOC and L-AmB were similar, but on the basis of time-kill studies, the fungicidal activity of L-AmB was significantly less than that of AmB-DOC. In immunocompetent mice, the dosage of AmB-DOC was limited by toxicity, resulting in a maximum tolerated dosage (MTD) of 0.4 mg/kg/day during treatment for 5 days; L-AMB was less toxic, the MTD being 7 mg/kg/day following a treatment period of the same duration. Both AmB-DOC and L-AmB led to significant reductions in the numbers of C. albicans in the kidneys of these mice and prevented relapse of infection after completion of treatment. Fluconazole in dosages of 0.4 and 64 mg/kg/day resulted in initial reductions in the numbers of cfu but failed to prevent relapse. In leucopenic mice, treatment for 5 days with AmB-DOC in a dosage of 0.3 mg/kg/day resulted in survival of the animals and a significant reduction in the numbers of cfu in the liver, spleen and lungs. However, there was no reduction in the number of cfu in the kidneys and this led to relapse of infection once therapy was terminated. Fluconazole in a dosage of 64 mg/kg/day produced effects which were similar to those of AmB-DOC; prolonged treatment with fluconazole for 18 days did not improve the efficacy of this agent. Only treatment with high-dosage (7 mg/kg/day) L-AmB was effective in significantly reducing the numbers of cfu of C. albicans in the kidneys and other organs of leucopenic mice, as well as preventing relapse, even in severely infected animals.

Impact of the duration of infection on the activity of ceftazidime, gentamicin and ciprofloxacin in Klebsiella pneumoniae pneumonia and septicemia in leukopenic rats.

An experimental Klebsiella pneumoniae pneumonia and septicemia in leukopenic rats was used to study the impact of the duration of infection on the bactericidal activity of ceftazidime, gentamicin and ciprofloxacin. It appeared that the number of bacteria persisting after a single intravenous injection progressively increased with delay of antibiotic administration up to 3 h after bacterial inoculation with each of the drugs tested. This effect was most pronounced for ciprofloxacin. An inoculum effect could not explain this decrease in bacterial killing. It was also observed that a single injection with a particular dose of each of the respective drugs did not kill all the Klebsiella pneumoniae organisms in the lung. Persisting bacteria did not represent a preexisting less susceptible subpopulation selected after antibiotic administration. In further experiments the impact of delay of the start of treatment on the efficacy of ceftazidime or ciprofloxacin after administration for a period of four days with intramuscular injections at 6 h intervals was investigated. Treatment was started at 5, 12 or 24 h after bacterial inoculation. The therapeutic efficacy of both drugs decreased with the increase of duration of infection, which may be at least in part due to the progressive number of bacteria persisting after antibiotic administration. These data underline the need to start antimicrobial treatment as soon as possible.

Influence of dose frequency on the therapeutic efficacies of ciprofloxacin and ceftazidime in experimental Klebsiella pneumoniae pneumonia and septicemia in relation to their bactericidal activities in vitro.

The antibacterial activities of ciprofloxacin versus ceftazidime against Klebsiella pneumoniae in vitro and in vivo were compared. Although there was only a minor difference in MBC values between both drugs ciprofloxacin demonstrated a high and dose-dependent bacterial killing rate in vitro and in lungs of leukopenic rats in contrast to the more time-dependent bactericidal activity of ceftazidime. After treatment of a K.pneumoniae pneumonia and septicemia the efficacy of ciprofloxacin was only slightly influenced by the mode of administration, either at 6-h intervals or continuously, whereas ceftazidime was far more effective after continuous administration. This resulted in a superior efficacy of ciprofloxacin after intermittent treatment as compared to ceftazidime, whereas ceftazidime was more effective after continuous administration as compared to ciprofloxacin. Also ciprofloxacin proved to be bactericidal against bacteria that were not actively growing, both in vitro and in vivo, whereas ceftazidime was not.

Continuous versus intermittent administration of ceftazidime in experimental Klebsiella pneumoniae pneumonia in normal and leukopenic rats.

Experimental Klebsiella pneumoniae pneumonia was used to study the influence of cyclophosphamide-induced leukopenia on the relative therapeutic efficacy of continuous and intermittent (6-h intervals) administration of ceftazidime. The antimicrobial response was evaluated with respect to the calculated daily dose that protected 50% of the animals from death (PD50) until 16 days after the termination of a 4-day treatment. When ceftazidime was administered intermittently to leukopenic rats, the PD50 was 24.37 mg/kg per day, 70 times (P less than 0.001) the PD50 of 0.35 mg/kg per day for normal rats. Continuous administration of ceftazidime to leukopenic rats resulted in a PD50 of 1.52 mg/kg per day, four times (P less than 0.001) the PD50 of 0.36 mg/kg per day for normal rats. Continuous administration of ceftazidime in daily doses that protected 100% of normal and leukopenic rats from death resulted in serum levels of 0.06 and 0.38 micrograms/ml, respectively, whereas the MIC for the infecting K. pneumoniae strain was 0.2 micrograms of ceftazidime per ml. The effect of the duration of ceftazidime treatment by continuous infusion on the therapeutic efficacy in relation to the persistence of leukopenia was then investigated in leukopenic rats. The administration of 3.75 mg of ceftazidime/kg per day for 4 days protected all leukopenic rats from death, provided the circulating leukocytes returned at the end of antibiotic treatment. When leukopenia persisted for 8 days this ceftazidime treatment schedule resulted in the mortality of rats (P less than 0.05). However, when ceftazidime treatment was continued for 8 days, until the return of the leukocytes, there was no significant mortality (P greater than 0.05).

Relevance of serum protein binding of cefoxitin and cefazolin to their activities against Klebsiella pneumoniae pneumonia in rats.

An experimental Klebsiella pneumoniae pneumonia in rats was used to study the effect of protein binding of cefoxitin and cefazolin on their therapeutic activity. Both cephalosporins were similar with respect to their antimicrobial activity against the K. pneumoniae in vitro, but they differed in their degree of protein binding, being 34% for cefoxitin and 89 to 93% for cefazolin in uninfected rats and 24 and 71 to 83%, respectively, in infected rats. Various doses of these agents were administered by continuous infusion, which started 5 h after bacterial inoculation and continued for 65 h. Antimicrobial response was evaluated with respect to the numbers of bacteria recovered from lung and blood at the end of treatment. An inhibitory effect of protein binding on the in vivo antimicrobial activity was demonstrated. Cefoxitin was therapeutically effective at a constant plasma level that reached the MIC. To obtain a similar effect with cefazolin the plasma level of that drug had to be increased to a concentration more than three times the MIC.

Therapeutic activities of cefazolin, cefotaxime, and ceftazidime against experimentally induced Klebsiella pneumoniae pneumonia in rats.

The efficacies of several dosage schedules of cefazolin, cefotaxime, and ceftazidime, started 12 or 36 h after infection, were examined in experimental pneumonia caused by Klebsiella pneumoniae in rats. The therapeutic activities of the cephalosporins were compared with the antibacterial activities in vitro and the serum concentration curves. The course of experimental pneumonia was rapid and characterized by tissue necrosis. Response to antimicrobial treatment was evaluated with respect to mortality and numbers of bacteria in lung (left lobe), blood, and pleural fluid. When antibiotic treatment was started early, i.e., 12 h after bacterial inoculation, cefotaxime and ceftazidime were equally effective and superior to cefazolin. Eleven doses of 10 mg of cefotaxime or ceftazidime per kg or 11 doses of 60 mg of cefazolin per kg were required to improve the survival rate. With a delay in administration to 36 h after inoculation, the efficacy of the cephalosporins decreased markedly. In the three dosages tested, cefazolin was ineffective. Survival improved with the administration of nine doses of 60 mg of cefotaxime per kg or nine doses of 10 mg of ceftazidime per kg. These results are not in accordance with the ratio of in vitro activities of cefotaxime and ceftazidime or the serum concentration curves.