Intentional isoniazid overdosage among southwestern American Indians.

A 30-month study explored the degree to which self-destructive behavior compromised tuberculosis therapy and prophylaxis among southwestern American Indians. The frequency of isoniazid (INH) overdosage paralleled the extent of INH usage in each tribe and the entent to which INH was perscribed for each tuberculosis category. The authors recommend the careful selection of patients for INH prophylaxis, the dispensing of small amounts at short intervals, the close monitoring of patient compliance with the prescribed drug regimen, and, possiblly, the dispensing of individually wrapped tablets to inhibit the impulsive ingestion of massive amounts of the drug.

Quantitative structure-activity relationships for the in vitro antimycobacterial activity of pyrazinoic acid esters.

Substituted pyrazinoic acid esters have previously been reported to have in vitro activity against Mycobacterium avium and Mycobacterium kansasii as well as Mycobacterium tuberculosis. Modification of both the pyrazine nucleus and the ester functionality was successful in expanding the antimycobacterial activity associated with pyrazinamide to include M. avium and M. kansasii, organisms usually not susceptible to pyrazinamide. In an attempt to understand the relationship between the activity of the esters with the needed biostability, a quantitative structure-activity relationship has been developed. This derived relationship is consistent with the observation that tert-butyl 5-chloropyrazinoate (13) and 2'-(2'-methyldecyl) 5-chloropyrazinoate (25), compounds which are both 100-fold more active than pyrazinamide against M. tuberculosis and possess a serum stability 900-1000 times greater than the lead compounds in the series.

Antimycobacterial activity of a series of pyrazinoic acid esters.

A series of pyrazinoic acid esters has been prepared and evaluated for in vitro antimycobacterial activity. Several of the pyrazinoate esters have substantially better activity than the first-line antituberculous agent pyrazinamide against susceptible isolates of Mycobacterium turberculosis as well as activity against pyrazinamide-resistant isolates. The minimal inhibitory concentrations (MICs) were lower for each organism and at each pH than the MICs for pyrazinamide. The esters have activity against Mycobacterium bovis and Mycobacterium kansasii, two species resistant to pyrazinamide, but not against Mycobacterium avium complex.

Pyrazinoic acid esters with broad spectrum in vitro antimycobacterial activity.

A series of substituted pyrazinoic acid esters has been prepared and examined for their in vitro activity against Mycobacterium avium and Mycobacterium kansasii as well as Mycobacterium tuberculosis. Modification of both the pyrazine nucleus and the ester functionality have been very successful in expanding the activity of pyrazinamide to include M. avium and M. kansasii, organisms normally not susceptible to pyrazinamide. Several of these compounds have activities 100-1000-fold greater than that of pyrazinamide against M. tuberculosis.

Identification of a novel oxazolidinone (U-100480) with potent antimycobacterial activity.

During the course of our investigations in the oxazolidinone antibacterial agent area, we have identified a subclass with especially potent in vitro activity against mycobacteria. The salient structural feature of these oxazolidinone analogues, 6 (U-100480), 7 (U-101603), and 8 (U-101244), is their appended thiomorpholine moiety. The rational design, synthesis, and evaluation of the in vitro antimycobacterial activity of these analogues is described. Potent activity against a screening strain of Mycobacterium tuberculosis was demonstrated by 6 and 7 (minimum inhibitory concentrations or MIC's < or = 0.125 micrograms/mL). Oxazolidinones 6 and 8 exhibit MIC90 values of 0.50 micrograms/mL or less against a panel of organisms consisting of five drug-sensitive and five multidrug-resistant strains of M. tuberculosis, with 6 being the most active congener. Potent in vitro activity against other mycobacterial species was also demonstrated by 6. For example, 6 exhibited excellent in vitro activity against multiple clinical isolates of Mycobacterium avium complex (MIC's = 0.5-4 micrograms/mL). Orally administered 6 displays in vivo efficacy against M. tuberculosis and M. avium similar to that of clinical comparators isoniazid and azithromycin, respectively. Consideration of these factors, along with a favorable pharmaco-kinetic and chronic toxicity profile in rats, suggests that 6 (U-100480) is a promising antimycobacterial agent.

Comparative in vitro activities of ampicillin, BMY 28142, and imipenem against Mycobacterium avium complex.

The in vitro activity of ampicillin, BMY 28142, and imipenem was evaluated against 21 clinical isolates of Mycobacterium avium complex by both a broth and an agar dilution method. The MIC90 by broth dilution for ampicillin, BMY 28142, and imipenem was 16 micrograms/ml, 8 micrograms/ml, and greater than 32 micrograms/ml, respectively. The MIC90 by agar dilution for ampicillin and BMY 28142 was 16 micrograms/ml.

Genome and MIC stability in Mycobacterium tuberculosis and indications for continuation of use of isoniazid in multidrug-resistant tuberculosis.

Mycobacterium tuberculosis strains resistant to two or more of the first line antituberculosis drugs (MDR) are a serious threat to successful tuberculosis control programmes. For this retrospective study, 85 follow-up drug resistant isolates from 23 patients residing in a community with a high incidence of tuberculosis were collected and the level of in-vitro resistance to antibiotics determined quantitatively. PCR-SSCP and sequencing techniques were used to screen for gene mutations associated with resistance in 31 follow-up samples from a smaller group of eight patients. DNA fingerprint analysis was done on sequential isolates to confirm identity. Although treatment had a profound effect on changes in drug resistance patterns, the MIC for a particular agent remained constant in follow-up isolates. DNA fingerprinting and mutational analysis (14 different loci) showed that the genome of MDR strains of M. tuberculosis is relatively stable during the course of therapy. The rpoB gene was the most frequently mutated structural gene involved in drug resistance and a novel C to T mutation upstream of open reading frame (ORF)1 of the inhA operon was detected. No evidence was found of the presence of strain W (New York) in this group of MDR strains. The results stress the importance of confirming individuality of strains for the accurate calculation of frequencies of particular mutations associated with drug resistance, particularly in a high incidence area. Approximately one-half (47.8%) of the patients had isolates resistant to concentrations just above the critical concentration for isoniazid (MICs of 0.2-5 mg/L). Therefore, these patients and their contacts who develop primary drug-resistant tuberculosis may respond to higher dosages of treatment which could have a considerable impact on the cost and the ease of management of resistant tuberculosis.

New antimycobacterial agents.

Development of new antimycobacterial agents has gained impetus from the frequent occurrence of disseminated M. avium complex infections associated with the AIDS epidemic and the resurgence of tuberculosis. Promising new agents are being developed by modification of existing antimycobacterial agents (for example, aminoglycosides, macrolides, beta-lactams, and rifamycins) and by development of new therapeutic classes of drugs (for example, 4-quinolones). In addition, new drug delivery systems (liposome encapsulation) and immunomodulators may prove to be clinically useful in the treatment of some mycobacterial infections. New antimycobacterial agents will likely have their greatest impact on nontuberculous mycobacterial diseases because this is the area in which improved therapy is most needed. The specific role for new agents will be established only after more extensive study in animal models of mycobacterial infection is followed by controlled, randomized clinical trials.

Mycobacterium gordonae as a human hepato-peritoneal pathogen, with a review of the literature.

Mycobacterium gordonae was cultured from the liver of a 39-year-old woman who presented with ascites, weight loss, and fever. Laparoscopic examination revealed white nodules studding the peritoneum and liver surface, and histopathology revealed caseating granulomas. She was successfully treated with rifampin, ethambutol, and isoniazid. A review of the literature on M. gordonae as a human pathogen in presented. Our patient represents the third reported case of disseminated disease due to this organism and the first to be successfully treated by medical therapy alone.

Comparative in vitro activities of MDL 473, rifampin, and ansamycin against Mycobacterium intracellulare.

The susceptibilities of 20 clinical isolates of Mycobacterium intracellulare to rifampin, MDL 473, and ansamycin were determined by broth and agar dilution methods. Ansamycin was more active than MDL 473, which in turn was usually more active than rifampin by either method. The MICs for 90% of the strains tested by agar dilution were 1, 2, and 4 micrograms of ansamycin, MDL 473, and rifampin per ml, respectively.

Comparative in vitro activities of ciprofloxacin and other 4-quinolones against Mycobacterium tuberculosis and Mycobacterium intracellulare.

The in vitro activity of ciprofloxacin, ofloxacin, amifloxacin, and norfloxacin against 22 clinical isolates of Mycobacterium tuberculosis was evaluated by agar dilution. The MICs for 90% of the isolates of ciprofloxacin and ofloxacin were 0.5 and 1 microgram/ml, respectively. Amifloxacin and norfloxacin were less active. The MICs for 90% of the isolates of ciprofloxacin and ofloxacin against 20 clinical isolates of Mycobacterium intracellulare were determined by agar dilution to be 2 and 8 micrograms/ml, respectively.

In vitro evaluation of nicotinamide riboside analogs against Haemophilus influenzae.

Exogenous NAD, nicotinamide mononucleotide, or nicotinamide riboside is required for the growth of Haemophilus influenzae. These compounds have been defined as the V-factor growth requirement. We have previously shown that the internalization of nicotinamide riboside is energy dependent and carrier mediated with saturation kinetics. Thionicotinamide riboside, 3-pyridinealdehyde riboside, 3-acetylpyridine riboside, and 3-aminopyridine riboside were prepared from their corresponding NAD analogs. These compounds and several other nicotinamide riboside analogs were evaluated for their ability to support the growth of H. influenzae and for their ability to block the uptake of [carbonyl-14C]nicotinamide riboside by H. influenzae. 3-Aminopyridine riboside blocked the uptake of [carbonyl-14C]nicotinamide riboside and inhibited the growth of H. influenzae when NAD, nicotinamide mononucleotide, or nicotinamide riboside served as the V factor. The antibacterial activity of 3-aminopyridine riboside was found to be specific for H. influenzae but had no effect on the growth of Staphylococcus aureus or Escherichia coli. In additional experiments by reversed-phase high-performance liquid chromatography, it was determined that whole cells of H. influenzae degrade 3-aminopyridine adenine dinucleotide to 3-aminopyridine riboside, which is then internalized. Inside the cell, 3-aminopyridine riboside has the ability to interfere with the growth of H. influenzae by an undetermined mechanism.

In vitro susceptibility of Mycobacterium fortuitum to amoxicillin or cephalothin in combination with clavulanic acid.

The comparative in vitro activity of cefoxitin, cephalothin, amoxicillin, and clavulanic acid in combination with the latter two agents against 13 isolates of Mycobacterium fortuitum was evaluated by agar dilution susceptibility testing. Amoxicillin was more active than cephalothin but less active than cefoxitin against the strains tested. Clavulanic acid in combination with these beta-lactams usually improved the activity by one or two dilutions compared with the beta-lactams alone.

Activity of azithromycin against Mycobacterium avium infection in beige mice.

The comparative activities of azithromycin and clarithromycin and the activities of azithromycin alone and in combination with other antimycobacterial agents were evaluated in the beige mouse model of disseminated Mycobacterium avium complex infection. Azithromycin was similar in activity to clarithromycin. Azithromycin plus clofazimine plus ethambutol reduced the number of splenic organisms more than azithromycin alone, while the combination was less active than azithromycin alone for bacteria in lungs. Rifabutin had activity similar to that of azithromycin for organisms in spleens and lungs. Rifabutin plus azithromycin was more active than either agent alone for organisms in spleens, but the combination's activity was not significantly different from that of rifabutin for organisms in lungs. The activity of azithromycin against several M. avium complex isolates was evaluated. The reduction of viable cell counts in spleens ranged from 1.7 to 0.8 log units. For the three isolates studied, there was little correlation between the in vitro MIC and the in vivo activity.

In vivo activities of newer rifamycin analogs against Mycobacterium avium infection.

The comparative activities of newer rifamycin analogs and the activity of rifabutin or rifapentine in combination with other antimycobacterial agents was evaluated in the beige (C57BL/6J; bgj/bgj) mouse model of disseminated Mycobacterium avium infection. Rifabutin and rifapentine at 20 mg/kg of body weight had comparable activities. P/DEA and CGP 7040 at 20 mg/kg were less active. The combination of ethambutol at 125 mg/kg and rifabutin at 20 mg/kg resulted in a slight increase in activity beyond that seen with rifabutin alone against organisms in the spleens. The combination of ethambutol and rifapentine at 20 mg/kg resulted in a modest increase in activity beyond that seen with rifapentine alone against organisms in the lungs. The combination of ethionamide at 125 mg/kg and rifapentine resulted in a decrease in activity compared with that for rifapentine alone. The combination of clofazimine at 20 mg/kg and rifapentine resulted in increased activity in the mouse model. The combination of clofazimine and rifapentine (or rifabutin) appears to be an attractive regimen that should be evaluated for the treatment of human infections due to M. avium complex.

Activity of KRM-1648 in combination with isoniazid against Mycobacterium tuberculosis in a murine model.

The activity of KRM-1648, alone and in combination with isoniazid, was compared with those of isoniazid, rifampin, and the combination of rifampin plus isoniazid in a murine model of tuberculosis. Four-week-old female CD-1 mice were infected intravenously with approximately 10(7) viable Mycobacterium tuberculosis ATCC 35801 organisms. Treatment was started 1 week postinfection and was given by gavage 5 days per week. The duration of the treatment phase was 12 weeks, with groups of mice sacrificed at 2, 4, 6, 8, and 12 weeks. For the observation phase, additional groups of treated mice were sacrificed at 4, 8, 16, and 24 weeks after the cessation of treatment. Viable cell counts were determined from homogenates of the spleens and the right lungs. KRM-1648 was the most active single agent evaluated and resulted in no detectable CFUs in the spleens and lungs by the end of 6 weeks of treatment. Neither rifampin nor isoniazid reduced cell counts to undetectable levels, even after 12 weeks of treatment. The combination of KRM-1648 plus isoniazid was much more active than rifampin plus isoniazid. KRM-1648 plus isoniazid resulted in the apparent sterilization of organs at 6 months following the cessation of treatment. The promising activity of KRM-1648 may allow for ultrashort-course therapy of tuberculosis, i.e., treatment regimens of 4 months or less.

Activities of azithromycin and clarithromycin against nontuberculous mycobacteria in beige mice.

The comparative activities of azithromycin (AZI) and clarithromycin (CLA) were evaluated against nontuberculous mycobacteria in a murine model of disseminated infection. Four-week-old beige mice (C57BL/6J bgj/bgj) were infected intravenously with approximately 10(7) viable Mycobacterium kansasii, M. xenopi, M. simiae, or M. malmoense. Treatment with AZI at 200 mg/kg, CLA at 200 mg/kg, ethambutol at 125 mg/kg, rifampin at 20 mg/kg, or clofazimine at 20 mg/kg of body weight was started 7 days postinfection, and the treatments were administered 5 days per week for 4 weeks. Control groups were sacrificed at the start and end of the treatments. Spleens and lungs were homogenized, and viable cell counts were determined by serial dilution and plating onto 7H10 agar. AZI and CLA had activities comparable to or better than that of rifampin, ethamutol, or clofazimine against these nontuberculous mycobacteria in the beige mouse test system. AZI at 200 mg/kg was more active than CLA at 200 mg/kg against organisms in the spleens for M. xenopi and M. malmoense. The activities of AZI and CLA were comparable against organisms in the spleens for M. kansasii and M. simiae. The activities of these two agents were comparable against organisms in the lungs for all four nontuberculous mycobacterial species. AZI or CLA in combination with other agents may be useful for the therapy of nontuberculous mycobacterial infections in humans.

Intermittent azithromycin for treatment of Mycobacterium avium infection in beige mice.

The activity of azithromycin (AZI) was evaluated in the beige mouse model of disseminated Mycobacterium avium infection. Mice were infected intravenously with approximately 10(7) viable avium ATCC 49601. AZI at 50, 100, or 200 mg/kg of body weight or clarithromycin (CLA) at 200 mg/kg was given by gavage 5 days per week for 4 weeks. Groups of treated mice were compared with untreated control animals. A dose-related reduction in cell counts in organs was observed with AZI treatment. AZI at 200 mg/kg was more active than CLA at 200 mg/kg against organisms in spleens. The activities of these two agents at 200 mg/kg were comparable against organisms in lungs. In a second study, AZI at 200 mg/kg was given daily for 5 days; this was followed by intermittent AZI treatment for the next 3 weeks. The activities of AZI given on a three-times- and five-times-per-week basis in the continuation phase were comparable. AZI given on a once-weekly basis was less active. The regimen of AZI given in combination with rifapentine on a once-weekly basis for 8 weeks showed promising activity. Clinical evaluation of AZI and rifapentine will help to define the roles of these agents in the treatment of disseminated M. avium complex infection.

Activity of rifapentine against Mycobacterium avium infection in beige mice.

The activity of rifapentine (MDL 473) was evaluated in the beige (C57BL/6J-bgj/bgj) mouse model of disseminated Mycobacterium avium infection. Approximately 10(7) cfu of M. avium, serotype 1, were given iv. Seven days later treatment was started with intraperitoneal rifapentine at 20 mg/kg of body weight. Treatment was given daily for five days followed by twice weekly for three weeks. The mice were killed two days after the last dose. Spleens, livers and lungs were homogenized and cfu/organ determined. Analysis of variance and Tukey honestly significant difference tests indicated that rifapentine reduced cfu in each of the organs compared with untreated controls. A dose-response experiment was performed with a daily rifapentine dose of 10, 20 or 40 mg/kg administered intraperitoneally. Dose-related reductions in cfu counts were observed in each of the organs. The activity of oral rifapentine at 20 mg/kg was demonstrated in a comparative experiment with rifampicin at 20, 40 or 60 mg/kg. Rifapentine significantly reduced cfu counts in organs compared with rifampicin. Rifapentine should be considered for further evaluation in the treatment of M. avium complex infection in humans.