Abstract: Daily rifapentine plus isoniazid-pyrazinamide in mice infected with Mycobacterium tuberculosis produces cure in 3 months. Whether cure corresponds to latent infection contained by host immunity or true tissue sterilization is unknown.
Abstract: Mycobacterium ulcerans causes Buruli ulcer, a potentially disabling ulcerative skin disease. Only recently was antimicrobial therapy proven effective. Treatment for 2 months with rifampin plus streptomycin was first proposed after experiments in the mouse footpad model demonstrated bactericidal activity. This treatment is now considered the treatment of choice, although larger ulcers may require adjunctive surgery. Shorter, oral regimens are desired, but evaluating drug activity in mice is hampered by the very slow growth of M. ulcerans, which takes 3 months to produce countable colonies. We created a recombinant bioluminescent M. ulcerans strain expressing luxAB from Vibrio harveyi for real-time evaluation of antimicrobial effects in vivo. Mouse footpads were injected with wild-type M. ulcerans 1059 (WtMu) or the recombinant bioluminescent strain (rMu). Two weeks later, mice received rifampin plus streptomycin, kanamycin alone (to which rMu is resistant), or streptomycin alone for 4 weeks and were observed for footpad swelling (preventive model). Untreated controls and kanamycin-treated rMu-infected mice received rifampin plus streptomycin for 4 weeks after developing footpad swelling (curative model). Compared to WtMu, rMu exhibited similar growth and virulence in vivo and similar drug susceptibility. A good correlation was observed between luminescence (measured as relative light units) and number of viable bacteria (measured by CFU) in footpad homogenates. Proof of concept was also shown for serial real-time evaluation of drug activity in live mice. These results indicate the potential of bioluminescence as a real-time surrogate marker for viable bacteria in mouse footpads to accelerate the identification of new treatments for Buruli ulcer.
Abstract: treatment of Mycobacterium ulcerans disease, or Buruli ulcer (BU), has shifted from surgery to treatment with streptomycin(STR)+rifampin(RIF) since 2004 based on studies in a mouse model and clinical trials. We tested two entirely oral regimens for BU treatment, rifampin(RIF)+clarithromycin(CLR) and rifapentine(RPT)+clarithromycin(CLR) in the mouse model.
Abstract: In a randomized controlled trial in Ghana, treatment of Mycobacterium ulcerans infection with streptomycin (SM)-rifampin (RIF) for 8 weeks was compared with treatment with SM-RIF for 4 weeks followed by treatment with RIF-clarithromycin (CLA) for 4 weeks. The extent of the interaction of RIF and CLA combined on the pharmacokinetics of the two compounds is unknown in this population and was therefore studied in a subset of patients. Patients received CLA at a dose of 7.5 mg/kg of body weight once daily, rounded to the nearest 125 mg. RIF was administered at a dose of 10 mg/kg, rounded to the nearest 150 mg. SM was given at a dose of 15 mg/kg once daily as an intramuscular injection. Plasma samples were drawn at steady state and analyzed by liquid chromatography-tandem mass spectroscopy. Pharmacokinetic parameters were calculated with the MW/Pharm (version 3.60) program. Comedication with CLA resulted in a 60% statistically nonsignificant increase in the area under the plasma concentration-time curve (AUC) for RIF of 25.8 mg x h/liter (interquartile ratio [IQR], 21.7 to 31.5 mg x h/liter), whereas the AUC of RIF was 15.2 mg x h/liter (IQR, 15.0 to 17.5 mg x h/liter) in patients comedicated with SM (P = 0.09). The median AUCs of CLA and 14-hydroxyclarithromycin (14OH-CLA) were 2.9 mg x h/liter (IQR, 1.5 to 3.8 mg x h/liter) and 8.0 mg x h/liter (IQR, 6.7 to 8.6 mg x h/liter), respectively. The median concentration of CLA was above the MIC of M. ulcerans, but that of 14OH-CLA was not. In further clinical studies, a dose of CLA of 7.5 mg/kg twice daily should be used (or with an extended-release formulation, 15 mg/kg should be used) to ensure higher levels of exposure to CLA and an increase in the time above the MIC compared to those achieved with the currently used dose of 7.5 mg/kg once daily.
Abstract: To investigate the antagonism between isoniazid (INH) and rifampin (rifampicin) (RIF)-pyrazinamide (PZA) combination observed in Mycobacterium tuberculosis-infected mice, extensive pharmacokinetic studies of INH were performed and followed by experiments to assess the impact of increasing doses of INH on the antimicrobial activity of RIF-PZA combination. INH at 6.25 mg/kg of body weight produced a maximum concentration of drug in serum (Cmax) value of 4 microg/ml and an area under the concentration-time curve from 0 to 24 h (AUC(0-24)) value of 4.9 microg x h/ml, the former being close to the Cmax value observed after the standard 5-mg/kg dose in humans. INH at 25 mg/kg produced a Cmax value of 22 microg/ml and an AUC(0-24) value of 29 microg x h/ml, the latter being close to the AUC observed after a 5-mg/kg dose of INH in humans with the slow acetylation phenotype. Beginning 2 weeks after aerosol infection with M. tuberculosis, mice were treated for 8 weeks with INH at twofold-increasing doses, ranging from 1.56 to 50 mg/kg, either alone or in combination with RIF-PZA. Given alone, INH exhibited dose-dependent activity. Combined with RIF-PZA, INH exhibited dose-dependent antagonism of RIF-PZA activity. To determine the individual components of RIF-PZA combination with which INH was antagonistic, mice were treated for 8 weeks with RIF alone, PZA alone, RIF-PZA, and INH at 3.125, 12.5, or 50 mg/kg either alone or combined with RIF or PZA. Addition of INH to RIF had additive activity, whereas addition of INH to PZA resulted in a negative interaction. Finally, a 10-mg/kg dose of INH in mice may best represent the 5-mg/kg dose in humans and decrease the antagonism of INH with RIF-PZA.
Abstract: PA-824 is a nitroimidazo-oxazine in clinical testing for the treatment of tuberculosis. We report that the novel combination of PA-824, moxifloxacin, and pyrazinamide cured mice more rapidly than the first-line regimen of rifampin, isoniazid, and pyrazinamide. If applicable to humans, regimens containing this combination may radically shorten the treatment of multidrug-resistant tuberculosis.
Abstract: Combination therapy is the most effective strategy to prevent emergence of resistance during tuberculosis (TB) treatment. Another strategy, albeit theoretical, is to limit the time that drug concentrations fall in the "mutant selection window" (MSW) between the MIC and the mutant prevention concentration (MPC). Drug concentrations above the MPC prevent selective amplification of resistant mutants in vitro even with a single drug exposure. The MSW concept has been validated using fluoroquinolones against Mycobacterium tuberculosis in vitro but not in vivo. Using a mouse model in which serum moxifloxacin (MXF) concentrations were maintained above the MPC, we tested whether this strategy prevents selection of MXF-resistant mutants. Beginning 2 weeks after aerosol infection with M. tuberculosis, when the mean lung log(10) CFU count was 7.9 +/- 0.2, mice received either no treatment or MXF in the diet at 0.25% to approximate the conventional human dose or 1.5% to maintain serum concentrations above the MPC (8 microg/ml). After 56 days of treatment, lung CFU counts were 3.5 +/- 0.8 and 0.9 +/- 0.6 in 0.25% and 1.5% of the MXF-treated mice, respectively. In mice given 0.25% MXF, MXF-resistant mutants were selected by day 28 and detected in 16% (3/19) of mice tested on day 56. No selection of MXF-resistant mutants was detected in mice given 1.5% MXF. We conclude that maintaining serum concentrations of MXF above the MPC prevents selection of MXF-resistant mutants. Although this target cannot be achieved clinically with MXF, it might be possible with new fluoroquinolones with more potent activity and/or improved pharmacokinetics.
Abstract: Unrecognized cross-contamination has been known to occur in laboratories frequently, especially with sensitive recovery system like BACTEC 460 TB. In March 2001, we investigated a pseudo-outbreak of Mycobacterium tuberculosis isolates in three smear negative clinical specimens and would like to present our experience in this communication.
Abstract: The creation of new chemotherapeutic regimens that permit shortening the duration of treatment is a major priority for antituberculosis drug development. In this study, we used the murine model of experimental tuberculosis therapy to determine whether incorporation of the investigational new nitroimidazopyran PA-824 into the standard first-line regimen has the potential to shorten the 6-month duration of treatment. As demonstrated previously, PA-824 alone had significant bactericidal activity over the first 2 months of treatment. Moreover, the substitution of PA-824 for isoniazid led to significantly lower lung CFU counts after 2 months of treatment and to more rapid culture-negative conversion compared to the standard regimen of rifampin, isoniazid, and pyrazinamide. Despite this, there was no difference in the proportion of mice relapsing after completing 6 months of therapy (2 of 19 mice treated with PA-824 in place of isoniazid relapsed versus 0 of 46 mice treated with the standard regimen). Meanwhile, no other PA-824-containing regimen tested was superior to the standard regimen on any assessment. Thus, we were unable to establish a clear role for PA-824 in a treatment-shortening regimen that includes two or more of the current first-line drugs. Future preclinical studies should include the evaluation of novel combinations of PA-824 with new drug candidates in addition to existing antituberculosis drugs for their potential to substantially improve the treatment of both drug-susceptible and multidrug-resistant tuberculosis.
Abstract: We report a high frequency (35%) of the Beijing genotype among multidrug-resistant isolates recovered in and around Mumbai, India. Further restriction fragment-length polymorphism typing showed that these strains were closely related. We also report a high frequency of the Delhi genotype (31% of isolates). Our data indicate considerable ongoing transmission of multidrug-resistant Mycobacterium tuberculosis strains of the Beijing genotype in Mumbai.
Abstract: We compared the incidence of multidrug resistance in 150 consecutive Mycobacterium tuberculosis isolates obtained from a rural center (in Sakawar, India) and an urban tertiary care center (in Mumbai, India). The study highlights an alarmingly high percentage of multidrug-resistant M. tuberculosis isolates in Mumbai (51%) as compared with that at the rural center (2%).
