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[Trends in tuberculosis treatment duration].

The two principal characteristics of tuberculosis treatment are its length (several months) and the need to use several antibiotics simultaneously (multiple drug therapy). Multiple drug therapy is intended to prevent the selection of resistant mutants at the beginning of treatment, when the bacilli population is largest. The length of treatment is due to dormant bacilli, which are much more difficult for antibiotics to kill than actively multiplying bacilli are. Rifampin and pyrazinamide are the most potent drugs against these dormant bacilli. The so-called sterilizing activity of rifampin has reduced the duration of treatment from 18 to 9 months, and the contribution of pyrazinamide reduced this time still further, to 6 months. When one of these drugs cannot be used because of resistance or toxicity, duration of treatment increases to the earlier levels. In the extreme case of multidrug-resistant tuberculosis where neither isoniazid nor rifampin can be used, and sometimes even not pyrazinamide, treatment is recommended for 18 to 24 months. New antituberculosis drugs under development allow us to envision further reduction in the duration of treatment of both drug-resistant and drug-sensitive tuberculosis.

Animals↗

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.

Anti-Bacterial Agents↗

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.

AIDS-Related Opportunistic Infections↗

A trial of three regimens to prevent tuberculosis in Ugandan adults infected with the human immunodeficiency virus. Uganda-Case Western Reserve University Research Collaboration.

BACKGROUND: Infection with the human immunodeficiency virus (HIV) greatly increases the risk of reactivation tuberculosis. We evaluated the safety and efficacy of three preventive-therapy regimens in a setting where exposure to tuberculosis is common. METHODS: We performed a randomized, placebo-controlled trial in 2736 HIV-infected adults recruited in Kampala, Uganda. Subjects with positive tuberculin skin tests (induration, > or =5 mm) with purified protein derivative (PPD) were randomly assigned to one of four regimens: placebo (464 subjects), isoniazid daily for six months (536), isoniazid and rifampin daily for three months (556), or isoniazid, rifampin, and pyrazinamide daily for three months (462). Subjects with anergy (0 mm induration in reaction to PPD and candida antigens) were randomly assigned to receive either placebo (323 subjects) or six months of isoniazid (395). The medications were dispensed monthly and were self-administered. RESULTS: Among the PPD-positive subjects, the incidence of tuberculosis in the three groups that received preventive therapy was lower than the rate in the placebo group (P=0.002 by the log-rank test). The relative risk of tuberculosis with isoniazid alone, as compared with placebo, was 0.33 (95 percent confidence interval, 0.14 to 0.77); with isoniazid and rifampin, 0.40 (0.18 to 0.86); and with isoniazid, rifampin, and pyrazinamide, 0.51 (0.24 to 1.08). Among the subjects with anergy, the relative risk of tuberculosis was 0.83 (95 percent confidence interval, 0.34 to 2.04) with isoniazid as compared with placebo. Side effects were more common with the multidrug regimens, and particularly with the regimen containing pyrazinamide. Survival did not differ among the groups, but the subjects with anergy had a higher mortality rate than the PPD-positive subjects. CONCLUSIONS: A six-month course of isoniazid confers short-term protection against tuberculosis among PPD-positive, HIV-infected adults. Multidrug regimens with isoniazid and rifampin taken for three months also reduce the risk of tuberculosis.

AIDS-Related Opportunistic Infections↗

Safety and completion rate of short-course therapy for treatment of latent tuberculosis infection.

BACKGROUND: Nine months of isoniazid therapy is the recommended regimen for treatment of latent tuberculosis infection, but low completion rates are a serious problem. The search for shorter regimens, compared with the standard isoniazid regimen, is of vital importance. We describe our experience using short-course regimens for the treatment of latent tuberculosis infection. METHODS: We conducted a nonrandomized, observational study of 459 patients in a county health department from June 2000 to January 2006. Short-course therapy was defined as pyrazinamide and rifampin taken daily or twice weekly for 2 months or rifampin taken daily for 4-6 months. Conventional therapy consisted of a 9-month regimen of isoniazid. Liver function testing was performed for both groups in accordance with clinical guidelines. Treatment completion and hepatotoxicity (according to the World Health Organization classification) were determined for the short-course and conventional therapy groups. RESULTS: Treatment was completed by 241 (77.7%) of 310 patients in the short-course group and by 98 (65.8%) of 149 patients in the isoniazid group (P = .009). Moderate to severe hepatotoxicity (grades 3 and 4) occurred in 6.1% of patients receiving short-course therapy and in 2.0% of patients receiving isoniazid (P=.09). The hepatotoxicity observed in the short-course group was confined to patients receiving pyrazinamide and rifampin daily and was self limited in all cases after the medications were discontinued. CONCLUSIONS: The rate of treatment completion was significantly higher with short-course regimens, compared with the isoniazid regimen. Although the overall risk of hepatotoxicity in patients receiving pyrazinamide and rifampin daily for the treatment of latent tuberculosis infection was higher, liver functions returned to normal after the medications were discontinued.

Adult↗

Pharmacokinetics of antimycobacterial drugs in patients with tuberculosis, AIDS, and diarrhea.

To test the hypothesis that antituberculous drug disposition is altered in patients with AIDS, we studied the steady-state pharmacokinetics of isoniazid (300 mg/d), rifampin (600 mg/d), and pyrazinamide (1,500 mg/d) in 29 adults (14 patients infected with human immunodeficiency virus [HIV] and 15 non-HIV-infected patients) with tuberculosis in Nairobi, Kenya. Intestinal integrity was assessed with xylose. Neither HIV infection nor diarrhea accounted for the interpatient variability in the area-under-the-plasma concentration vs. time curve (AUC), the maximum concentration, or the terminal half-life (t1/2) of isoniazid, rifampin, and pyrazinamide. No significant association between HIV infection or diarrhea and pharmacokinetics was seen for any of the compounds. In addition, neither the AUC nor the t1/2 of any of these drugs reflected interpatient differences in CD4 lymphocyte counts. Xylose absorption was uniformly low. We did not demonstrate that HIV infection, diarrhea, or CD4 lymphocyte counts contributed significantly to the variability in pharmacokinetics of isoniazid, rifampin, and pyrazinamide in TB patients in Nairobi.

AIDS-Related Opportunistic Infections↗

Poly (DL-lactide-co-glycolide) nanoparticle-based inhalable sustained drug delivery system for experimental tuberculosis.

OBJECTIVES: To improve the bioavailability of antitubercular drugs (ATDs) as well as to assess the feasibility of administering ATDs via the respiratory route, this study reports the formulation of three frontline ATDs, i.e. rifampicin, isoniazid and pyrazinamide encapsulated in poly (DL-lactide-co-glycolide) nanoparticles suitable for nebulization. METHODS: Drug-loaded nanoparticles were prepared by the multiple emulsion technique, vacuum-dried and nebulized to guinea pigs. The formulation was evaluated with respect to the pharmacokinetics of each drug and its chemotherapeutic potential in Mycobacterium tuberculosis infected guinea pigs. RESULTS: The aerosolized particles exhibited a mass median aerodynamic diameter of 1.88 +/- 0.11 microm, favourable for bronchoalveolar lung delivery. A single nebulization to guinea pigs resulted in sustained therapeutic drug levels in the plasma for 6-8 days and in the lungs for up to 11 days. The elimination half-life and mean residence time of the drugs were significantly prolonged compared to when the parent drugs were administered orally, resulting in an enhanced relative bioavailability (compared to oral administration) for encapsulated drugs (12.7-, 32.8- and 14.7-fold for rifampicin, isoniazid and pyrazinamide, respectively). The absolute bioavailability [compared to intravenous (i.v.) administration] was also increased by 6.5-, 19.1- and 13.4-fold for rifampicin, isoniazid and pyrazinamide, respectively. On nebulization of nanoparticles containing drugs to M. tuberculosis infected guinea pigs at every 10th day, no tubercle bacilli could be detected in the lung after five doses of treatment whereas 46 daily doses of orally administered drug were required to obtain an equivalent therapeutic benefit. CONCLUSIONS: Nebulization of nanoparticles-based ATDs forms a sound basis for improving drug bioavailability and reducing the dosing frequency for better management of pulmonary tuberculosis.

Administration, Inhalation↗

The influence of co-administered organic acids on the kinetics and dynamics of frusemide.

1. This study examines the effects of pretreatment with probenecid with and without pyrazinamide on the elimination kinetics and diuretic action of frusemide. 2. Six normal male volunteers received 40 mg frusemide i.v. on three occasions; i.e. once on its own and twice after pretreatment with 2 g probenecid with and without 3 g pyrazinamide. Both these latter drugs were administered orally 3 h before frusemide administration thereby attempting optimal suppression of proximal tubular secretion. Urinary losses were replaced i.v. with isovolumetric amounts of normal saline while insensible losses were compensated for by taking tap water orally. 3. The mean cumulative urinary frusemide excretion was significantly and similarly decreased by pretreatment with probenecid (34.9%) and probenecid plus pyrazinamide (33.6%), but the mean total volume of diuresis and the mean cumulative urinary sodium excretion did not differ significantly between treatments over the 5 h period. 4. The diuretic efficiency of frusemide was significantly increased with probenecid pretreatment during the first 90 min period after frusemide administration. Furthermore, in the first 30 min after administration the percent sodium fractional excretion was higher after pretreatment with probenecid even though the mean frusemide excretion rate was more than three times with frusemide alone than with probenecid-frusemide (374.4 micrograms min-1 vs 119.1 micrograms min-1). Pretreatment with probenecid results in a higher concentration on the peritubular or blood side of the tubules and these results lead us to question the unconditional acceptance of a luminal site of action for the loop diuretics. Alternatively, probenecid may act in some other way to increase the effects of frusemide.

Adult↗

Pyrazinoic acid and its n-propyl ester inhibit fatty acid synthase type I in replicating tubercle bacilli.

The activity of different analogs of pyrazinamide on Mycobacterium tuberculosis fatty acid synthase type I (FASI) in replicating bacilli was studied. Palmitic acid biosynthesis was diminished by 96% in bacilli treated with n-propyl pyrazinoate, 94% in bacilli treated with 5-chloro-pyrazinamide, and 97% in bacilli treated with pyrazinoic acid, the pharmacologically active agent of pyrazinamide. We conclude that the minimal structure of pyrazine ring with an acyl group is sufficient for FASI inhibition and antimycobacterial activity.

Bacterial Proteins↗

Activity and penetration of antituberculosis drugs in mouse peritoneal macrophages infected with Mycobacterium microti OV254.

The activities of some commonly used antituberculosis drugs were investigated within unstimulated peritoneal macrophages and in 7H-9 medium without Tween 80 using Mycobacterium microti OV254 as the target organism. In macrophage cultures, serial concentrations of isoniazid, rifampin, pyrazinamide, or streptomycin were added after a 2.5-h phagocytosis period. Viable counts were carried out at daily intervals for 5 or 6 days. The patterns of susceptibility to the four drugs were similar for M. microti and Mycobacterium tuberculosis. To ensure comparability with daily drug replacements in the macrophage experiments, the period of exposure to drugs in 7H-9 medium was kept to only 3 days. With in vitro culture at pH 6.4, drug penetration, measured as the ratio of MICs in macrophages to MICs in 7H-9 medium, was approximately 5 for isoniazid, 5 for rifampin, and 10 for streptomycin. With in vitro culture at pH 7.4, drug penetration was 100 for streptomycin, and at pH 5.6 it was 1 for pyrazinamide. Pyrazinamide was only bacteriostatic in macrophages but weakly bactericidal during the first day of exposure in vitro.

Animals↗

Activity of KRM-1648, a new benzoxazinorifamycin, against Mycobacterium tuberculosis in a murine model.

The activity of KRM-1648 was evaluated in a murine model of tuberculosis. Approximately 10(7) viable Mycobacterium tuberculosis ATCC 35801 organisms were given intravenously to 4-week-old female outbred mice. Treatment was started 1 week postinfection and given by gavage for 4 weeks. Viable-cell counts were determined from homogenates of spleen and lung tissues. The activity of KRM-1648 was compared with those of rifampin and rifabutin at 20 mg/kg of body weight. KRM-1648 was more active than either rifampin or rifabutin against organisms in spleens and lungs. KRM-1648 alone and in combination with either isoniazid, ethambutol, pyrazinamide, or levofloxacin was evaluated. Other treatment groups received isoniazid, ethambutol, pyrazinamide, or levofloxacin as single agents. KRM-1648 was the most active single agent evaluated. KRM-1648-pyrazinamide and KRM-1648-isoniazid were the most active combinations. These combinations were more active than KRM-1648 alone. The promising activity of KRM-1648 in M. tuberculosis-infected mice suggests that it is a good candidate for clinical development as a new antituberculosis agent.

Animals↗

Characterization of Mycobacterium smegmatis expressing the Mycobacterium tuberculosis fatty acid synthase I (fas1) gene.

Unlike most other bacteria, mycobacteria make fatty acids with the multidomain enzyme eukaryote-like fatty acid synthase I (FASI). Previous studies have demonstrated that the tuberculosis drug pyrazinamide and 5-chloro-pyrazinamide target FASI activity. Biochemical studies have revealed that in addition to C(16:0), Mycobacterium tuberculosis FASI synthesizes C(26:0) fatty acid, while the Mycobacterium smegmatis enzyme makes C(24:0) fatty acid. In order to express M. tuberculosis FASI in a rapidly growing Mycobacterium and to characterize the M. tuberculosis FASI in vivo, we constructed an M. smegmatis Deltafas1 strain which contained the M. tuberculosis fas1 homologue. The M. smegmatis Deltafas1 (attB::M. tuberculosis fas1) strain grew more slowly than the parental M. smegmatis strain and was more susceptible to 5-chloro-pyrazinamide. Surprisingly, while the M. smegmatis Deltafas1 (attB::M. tuberculosis fas1) strain produced C(26:0), it predominantly produced C(24:0). These results suggest that the fatty acid elongation that produces C(24:0) or C(26:0) in vivo is due to a complex interaction among FASI, FabH, and FASII and possibly other systems and is not solely due to FASI elongation, as previously suggested by in vitro studies.

Bacterial Proteins↗

Controlled clinical trial of four short-course regimens of chemotherapy for two durations in the treatment of pulmonary tuberculosis: first report: Third East African/British Medical Research Councils study.

A comparison was made between 4 regimens of chemotherapy given for 6 or 8 months, with a 6-month period of follow-up thus far. One regimen, which had a 2-month initial intensive phase of streptomycin, isoniazid, rifampin, and pyrazinamide followed by daily administration of thiacetazone and isoniazid, was very effective. Shortening the initial intensive 4-drug phase to 1 month produced a less successful regimen unless the continuation phase was twice-weekly administration of streptomycin, isoniazid, and pyrazinamide. A regimen in which pyrazinamide was omitted from the initial intensive 2-month phase was also less effective. All patients were inpatients for 6 months to ensure that every dose of drug was fully supervised during this period. Increasing the total duration of chemotherapy from 6 months to 8 months was associated with a significant decrease in the early relapse rate in all 4 regimens, although the above differences between the regimen remained. The applicability of the findings is discussed.

Adolescent↗

Incidence of serious side effects from first-line antituberculosis drugs among patients treated for active tuberculosis.

Major adverse reactions to antituberculosis drugs can cause significant morbidity, and compromise treatment regimens for tuberculosis (TB). Among patients treated for active TB we estimated the incidence, and risk factors, of major side effects from first-line anti-TB drugs. Side effects, resulting in modification or discontinuation of therapy, or hospitalization, were attributed on the basis of resolution after withdrawal, and/or recurrence with rechallenge. Among 430 patients treated between 1990 and 1999, the incidence of all major adverse effects was 1.48 per 100 person-months of exposure (95% confidence interval [95% CI], 1.31 to 1.61) for pyrazinamide, compared with 0.49 (95% CI, 0.42 to 0.55) for isoniazid, 0.43 (95% CI, 0.37 to 0.49) for rifampin, and 0.07 (95% CI, 0.04 to 0.10) for ethambutol. Occurrence of any major side effect was associated with female sex (adjusted hazard ratio, 2.5; 95% CI, 1.3 to 4.7), age over 60 years (adjusted hazard ratio, 2.9; 95% CI, 1.3 to 6.3), birthplace in Asia (adjusted hazard ratio, 2.5; 95% CI, 1.3 to 5.0), and human immunodeficiency virus-positive status (adjusted hazard ratio, 3.8; 95% CI, 1.05 to 13.4). Pyrazinamide-associated adverse events were associated with age over 60 years (adjusted hazard ratio, 2.6; 95% CI, 1.01 to 6.6) and birthplace in Asia (adjusted hazard ratio, 3.4; 95% CI, 1.4 to 8.3), whereas rifampin-associated adverse events were associated with age over 60 years (adjusted hazard ratio, 3.9; 95% CI, 1.02 to 14.9) and human immunodeficiency virus-positive status (adjusted hazard ratio, 8.0; 95% CI, 1.5 to 43). The incidence of pyrazinamide-induced hepatotoxicity and rash during treatment for active TB was substantially higher than with the other first-line anti-TB drugs, and higher than previously recognized.

Adolescent↗

Potent twice-weekly rifapentine-containing regimens in murine tuberculosis.

RATIONALE: Recent studies have demonstrated that intermittent administration of rifamycin-based regimens results in higher rates of tuberculosis relapse and treatment failure compared with daily therapy. Twice-weekly treatment with rifampin, isoniazid, and pyrazinamide may be improved by increasing Mycobacterium tuberculosis exposure to rifamycin by substituting rifapentine for rifampin. METHODS: To test this hypothesis, we compared the activities of standard daily and twice-weekly rifampin plus isoniazid-based regimens to those of twice-weekly rifapentine plus isoniazid- or moxifloxacin-containing regimens in the murine model of tuberculosis. Relapse rates were assessed after 4, 5, and 6 mo of treatment to assess stable cure. Single- and multiple-dose pharmacokinetics of rifampin and rifapentine were also determined. RESULTS: After 2 mo of treatment, twice-weekly therapy with rifapentine (15 or 20 mg/kg), moxifloxacin, and pyrazinamide was significantly more active than standard daily or twice-weekly therapy with rifampin, isoniazid, and pyrazinamide. Stable cure was achieved after 4 mo of twice-weekly rifapentine plus isoniazid- or moxifloxacin-containing therapy, but only after 6 mo of standard daily therapy. Twice-weekly rifapentine (15 mg/kg) displayed more favorable pharmacodynamics than did daily rifampin (10 mg/kg). CONCLUSIONS: By virtue of the enhanced rifamycin exposure, twice-weekly regimens containing rifapentine (15 or 20 mg/kg) may permit shortening the current treatment duration by 2 mo. Such regimens warrant clinical investigation.

Animals↗

Renal pathogenesis of familial hyperuricemia: studies in two kindreds.

The pathogenesis of familial hyperuricemia has been investigated in two kindreds in whom hyperuricemia was present in members of successive generations. Enzymatic and metabolic studies, including the incorporation of isotopically labeled glycine into urinary uric acid and assessment of the total excretion of oxypurines in one family, excluded a metabolic etiology. No secondary cause of hyperuricemia was identified in either family. Fractional excretion of uric acid was less than 6.2% in all hyperuricemic individuals studied, while creatinine clearances were normal. Tubular secretion of uric acid and tubular reabsorption of uric acid were studied in an affected teenager from each family while receiving a purine-free diet. Inhibition of secretion of uric acid with pyrazinamide decreased fractional excretion of uric acid to 0.6% in patient S and to 0.7% in patient B. Tubular secretion of uric acid at maximal response to pyrazinamide in these patients was 0.393 and 0.410 mg/dl glomerular filtration rate(nl response 0.300 to 1.30 mg/min/100ml inulin clearance). Probenecid, an inhibitor of uric acid reabsorption, increased uric acid excretion by 3.9 mg/min and by 3.2 mg/min (nl response 1.7 +/- 0.3 mg/min) in patients S and B. Tubular reabsorption of uric acid distal to secretory sites was determined by assessing the uricosuric response to probenecid plus pyrazinamide. Uric acid excretion increased by only 0.08 mg/min in patient A and by 0.17 mg/min in patient B (nl response 0.9 mg/min). Ascorbic acid increased fractional excretion of uric acid by 7.2% in patient S but was not uricosuric in patient B or any hyperuricemic member of his family. These data suggest that hyperuricemia in these families is due to diminished renal clearance of uric acid and that the reduced clearance is due to increased tubular reabsorption of uric acid distal to secretory sites.

Adolescent↗

Adverse events and treatment completion for latent tuberculosis in jail inmates and homeless persons.

BACKGROUND: Recently, a short-course treatment using 60 daily doses of rifampin and pyrazinamide was recommended for latent tuberculosis (TB) infection (LTBI). STUDY OBJECTIVES: To determine the acceptability, tolerability, and completion of treatment. DESIGN: Observational cohort study. SETTING: Five county jails and TB outreach clinics for homeless populations in three cities. PATIENTS: Study staff enrolled 1,211 patients (844 inmates and 367 homeless persons). INTERVENTIONS: Sites used 60 daily doses of rifampin and pyrazinamide, an approved treatment regimen for LTBI. MEASUREMENTS: Types and frequency of drug-related adverse events and outcomes of treatment. RESULTS: Prior to treatment, 25 of 1,178 patients (2.1%) had a serum aminotransferase measurement at least 2.5 times the upper limit of normal. Patients who reported excess alcohol use in the past 12 months were more likely than other patients to have an elevated pretreatment serum aminotransferase level (odds ratio, 2.1; 95% confidence interval, 1.1 to 6.1; p = 0.03). Treatment was stopped in 66 of 162 patients (13.4%) who had a drug-related adverse event. Among 715 patients who had serum aminotransferase measured during treatment, 43 patients (6.0%) had an elevation > 5 times the upper limits of normal, including one patient who died of liver failure attributed to treatment. In multivariate analyses, increasing age, an abnormal baseline aspartate aminotransferase level, and unemployment within the past 24 months were independent risk factors for hepatotoxicity. Completion rates were similar in jail inmates (47.5%) and homeless persons (43.6%). CONCLUSIONS: This study detected the first treatment-associated fatality with the rifampin and pyrazinamide regimen, prompting surveillance that detected unacceptable levels of hepatotoxicity and retraction of recommendations for its routine use. Completion rates for LTBI treatment using a short-course regimen exceeds historical rates using isoniazid. Efforts to identify an effective short-course treatment for LTBI should be given a high priority.

Adolescent↗

[Isoniazid-induced hepatic failure. Report of a case].

Isoniazid and pyrazinamide are both well-known hepatotoxic drugs. When isoniazid is used, the hepatic lesion appears before than when pyrazinamide is used. This paper intends to relate a case of a 5-month-old patient who had lungs' and meningeal tuberculosis and who developed toxic hepatitis accomplished by hepatic failure while he was being treated with isoniazid, pyrazinamide and rifampicin. The clinic manifestations and the laboratory alterations were detected in the fifth day of treatment and the recovery was fast; and almost complete by the end of the first week, in which the use of isoniazid had been suspended. Although it was necessary to take the patient to the intensive care unit, he had a good recovery, without sequels.

Antitubercular Agents↗