Supervised six-months treatment of newly diagnosed pulmonary tuberculosis using isoniazid, rifampin, and pyrazinamide with and without streptomycin

Comparing the Efficacy of Drug Regimens for Pulmonary Tuberculosis: Meta-analysis of Endpoints in Early-Phase Clinical Trials

Background

A systematic review of early clinical outcomes in tuberculosis was undertaken to determine ranking of efficacy of drugs and combinations, define variability of these measures on different endpoints, and to establish the relationships between them.

Methods

Studies were identified by searching PubMed, Medline, Embase, LILACS (Latin American and Caribbean Health Sciences Literature), and reference lists of included studies. Outcomes were early bactericidal activity results over 2, 7, and 14 days, and the proportion of patients with negative culture at 8 weeks.

Results

One hundred thirty-three trials reporting phase 2A (early bactericidal activity) and phase 2B (culture conversion at 2 months) outcomes were identified. Only 9 drug combinations were assessed on >1 phase 2A endpoint and only 3 were assessed in both phase 2A and 2B trials.

Conclusions

The existing evidence base supporting phase 2 methodology in tuberculosis is highly incomplete. In future, a broader range of drugs and combinations should be more consistently studied across a greater range of phase 2 endpoints.

Effect of duration and intermittency of rifampin on tuberculosis treatment outcomes: a systematic review and meta-analysis

BACKGROUND

Treatment regimens for active tuberculosis (TB) that are intermittent, or use rifampin during only the initial phase, offer practical advantages, but their efficacy has been questioned. We conducted a systematic review of treatment regimens for active TB, to assess the effect of duration and intermittency of rifampin use on TB treatment outcomes.

METHODS AND FINDINGS

PubMed, Embase, and the Cochrane CENTRAL database for clinical trials were searched for randomized controlled trials, published in English, French, or Spanish, between 1965 and June 2008. Selected studies utilized standardized treatment with rifampin-containing regimens. Studies reported bacteriologically confirmed failure and/or relapse in previously untreated patients with bacteriologically confirmed pulmonary TB. Pooled cumulative incidences of treatment outcomes and association with risk factors were computed with stratified random effects meta-analyses. Meta-regression was performed using a negative binomial regression model. A total of 57 trials with 312 arms and 21,472 participants were included in the analysis. Regimens utilizing rifampin only for the first 1-2 mo had significantly higher rates of failure, relapse, and acquired drug resistance, as compared to regimens that used rifampin for 6 mo. This was particularly evident when there was initial drug resistance to isoniazid, streptomycin, or both. On the other hand, there was little evidence of difference in failure or relapse with daily or intermittent schedules of treatment administration, although there was insufficient published evidence of the efficacy of twice-weekly rifampin administration throughout therapy.

CONCLUSIONS

TB treatment outcomes were significantly worse with shorter duration of rifampin, or with initial drug resistance to isoniazid and/or streptomycin. Treatment outcomes were similar with all intermittent schedules evaluated, but there is insufficient evidence to support administration of treatment twice weekly throughout therapy.

Why is long-term therapy required to cure tuberculosis?

The authors argue that understanding and countering general bacterial mechanisms of phenotypic antibiotic resistance may hold the key to reducing the duration of treatment of all recalcitrant bacterial infections, including tuberculosis.

Characterization of pncA mutations in pyrazinamide-resistant Mycobacterium tuberculosis in Brazil

In this study the nucleotide sequence of the pncA gene from 59 Mycobacterium tuberculosis clinical isolates was analyzed. Mutations in the pncA gene were identified in 29 of 40 pyrazinamide-resistant isolates, and no pyrazinamidase activity was detected in 39 of them. Twelve mutations found in this work have not been described previously.

Fixed-dose combination drugs for tuberculosis: application in standardised treatment regimens

Short-course chemotherapy is highly efficacious in treating tuberculosis (TB). However, the length (>/=6 months) and complexity (three or four different drugs) of the treatment makes adherence difficult. Erratic treatment not only fails to cure patients but also creates chronically contagious cases, who may excrete drug-resistant TB bacteria. The Directly Observed Treatment Short-course (DOTS) strategy recommended by WHO provides a comprehensive organisational and infrastructural framework for the rational use of diagnosis, drug supply, as well as case and programme management services, in TB control. WHO and other organisations recommend fixed-dose combination formulations (FDCs) as a further step to facilitate the optimal drug treatment of TB. Using FDCs in TB control will simplify the doctor's prescription and patient's drug intake, as well as the drug supply management of the programme. By preventing monotherapy and facilitating the ingestion of adequate doses of the constituent anti-TB drugs, FDCs are expected to help prevent the emergence of drug resistance. This article presents the international recommendations for the use of FDCs in TB programmes. The fundamental issue is to obtain drug supplies of good quality. A laboratory network for quality testing, including bioavailability testing of FDCs exists, and the recently established Global TB Drug Facility (GDF) supplies quality TB drugs, including 4-drug FDCs, to countries requesting assistance. This articles deals with the requirements for a successful transition to FDC-based treatment. It emphasises the need for appropriately revised programme documentation (programme manual, training modules, treatment guidelines and forms), training of staff at all levels, carefully calculated drug needs, and a plan for the exhaustion of existing stocks of loose tablets and the phasing-in of FDCs at all levels of the programme at the same time. Loose drugs for individualised treatment of patients with adverse effects should be kept at district or central health institutions.

Paediatric tuberculosis

Children are important in the epidemiology of tuberculosis as a marker of recent disease transmission and a reservoir for the future. Once infected they have a higher risk of progressing to tuberculous disease. Chest radiography and tuberculin testing with or without tissue for culture are still the standard tools for confirming the diagnosis once this is considered. Well researched treatment protocols are available but multidrug resistant tuberculosis and coexistent HIV are a challenge. Ensuring compliance with treatment is a major concern. Controversy still surrounds the place of BCG. Advances in the molecular genetics of tuberculosis hold out the possibility of better vaccines.

Evaluation of rifalazil in long-term treatment regimens for tuberculosis in mice

Previous experiments with rifalazil (RLZ) (also known as KRM-1648) in combination with isoniazid (INH) demonstrated its potential for short-course treatment of Mycobacterium tuberculosis infection. In this study we investigated the minimum RLZ-INH treatment time required to eradicate M. tuberculosis in a murine model. RLZ-INH treatment for 6 weeks or longer led to a nonculturable state. Groups of mice treated in parallel were killed following an observation period to evaluate regrowth. RLZ-INH treatment for a minimum of 10 weeks was necessary to maintain a nonculturable state through the observation period. Pyrazinamide (PZA) was added to this regimen to determine whether the treatment duration could be further reduced. In this model, the addition of PZA did not shorten the duration of RLZ-INH treatment required to eradicate M. tuberculosis from mice. The addition of PZA reduced the number of mice in which regrowth occurred, although the reduction was not statistically significant.

Pharmacokinetic factors in the modern drug treatment of tuberculosis

Tuberculosis is increasing in prevalence throughout the world, particularly in sub-Saharan Africa, Asia and Latin America. This resurgence can partly be attributed to increasing poverty, particularly in developing countries, and the human immunodeficiency virus (HIV) pandemic. However, there is also increasing concern at the development of multidrug-resistant tuberculosis caused by the misuse of the agents available. The modern treatment of patients with tuberculosis should start, in most cases, with 4 first-line agents in order to minimise the risk of drug resistance developing. A6-month drug regimen is usually satisfactory for pulmonary and nonpulmonary tuberculosis, although not for patients with tuberculous meningitis, in whom a longer course of treatment is required. Coinfection with HIV may produce an atypical clinical and radiological presentation, but the treatment regimen is essentially similar to other situations. Several of the first-line agents, in particular rifampicin (rifampin) and isoniazid, are likely to cause clinically significant drug interactions and/or toxicity, particularly in patients with HIV infection. Consideration of the pharmacodynamic and pharmacokinetic interactions between the host, the mycobacterium and the drug may contribute to the development of pharmacokinetically optimised regimens that make best use of the existing range of antituberculosis drugs. However, such idealised regimens need to be tested in prospective clinical trials. The use of therapeutic drug monitoring in selected groups of patients may improve outcomes, avoid drug toxicity and reduce the development of multidrug-resistant tuberculosis. The management of multidrug-resistant tuberculosis requires a high level of clinical expertise and such patients should start on at least 5 drugs to which the organism is thought to be susceptible. Up to 50% of patients with tuberculosis may not adhere to their drug regimen, resulting in persisting infectiousness, relapse or the development of drug resistance. Directly observed treatment with antituberculosis drugs, combined with a serious commitment to tuberculosis control, is required if we are to combat this increasing epidemic.

Tuberculosis in the AIDS era

A resurgence of tuberculosis has occurred in recent years in the United States and abroad. Deteriorating public health services, increasing numbers of immigrants from countries of endemicity, and coinfection with the human immunodeficiency virus (HIV) have contributed to the rise in the number of cases diagnosed in the United States. Outbreaks of resistant tuberculosis, which responds poorly to therapy, have occurred in hospitals and other settings, affecting patients and health care workers. This review covers the pathogenesis, epidemiology, clinical presentation, laboratory diagnosis, and treatment of Mycobacterium tuberculosis infection and disease. In addition, public health and hospital infection control strategies are detailed. Newer approaches to epidemiologic investigation, including use of restriction fragment length polymorphism analysis, are discussed. Detailed consideration of the interaction between HIV infection and tuberculosis is given. We also review the latest techniques in laboratory evaluation, including the radiometric culture system, DNA probes, and PCR. Current recommendations for therapy of tuberculosis, including multidrug-resistant tuberculosis, are given. Finally, the special problem of prophylaxis of persons exposed to multidrug-resistant tuberculosis is considered.

Current and potential treatment of tuberculosis

A recent resurgence of interest in tuberculosis as a global health problem has accompanied the resurgence of tuberculosis in both industrialised and developing countries. It has also been demonstrated recently that tuberculosis treatment and control is one of the most cost effective of all medical interventions. The human immunodeficiency virus (HIV) epidemic and increasing resistance to antituberculous drugs complicate our response to the problem of tuberculosis. Chemotherapy with currently available agents is highly effective, not only in pulmonary tuberculosis in adults, but also in extrapulmonary disease, and in disease in children and even patients with concomitant HIV infection. Short course chemotherapy and intermittent therapy are as effective as older regimens. Measures, including directly observed therapy, to maximise compliance with therapy, are of utmost importance. An efficient programme which assures compliance with effective antituberculosis chemotherapy should be a priority for health spending even in those countries with fewest resources.

Pharmacokinetics of pyrazinamide and its metabolites in healthy subjects

The plasma and urine pharmacokinetic parameters of pyrazinamide and of its metabolites (pyrazinoic acid, 5-hydroxy-pyrazinamide, 5-hydroxy-pyrazinoic acid and pyrazinuric acid) have been studied after a single oral dose of pyrazinamide 27 mg.kg-1 in 9 healthy subjects. Pyrazinamide was rapidly absorbed (tmax less than or equal to 1 h) and showed a short distribution phase followed by an elimination phase of t1/2 beta = 9.6 h. The close similarity of the apparent elimination rates of the metabolites led to a second trial of a single oral dose of pyrazinoic acid to evaluate the formation and elimination stages. The limiting factor was found to be the activity of a microsomal deamidase (pyrazinoic acid formation from pyrazinamide and 5-hydroxy-pyrazinoic acid formation from 5-hydroxy-pyrazinamide). In contrast, oxidation by xanthine oxidase occurred very rapidly (5-hydroxy-pyrazinamide formation and pyrazinoic acid catabolism to 5-hydroxy-pyrazinoic acid).