Infection caused by Mycobacterium tuberculosis

Synthesis and in vitro anti-mycobacterial activity of 5-substituted pyrimidine nucleosides

Mycobacterium tuberculosis and Mycobacterium avium infections cause the two most important mycobacterioses, leading to increased mortality in patients with AIDS. Various 5-substituted 2'-deoxyuridines, uridines, 2'-O-methyluridine, 2'-ribofluoro-2'-deoxyuridines, 3'-substituted-2',3'-dideoxy uridines, 2',3'-dideoxyuridines, and 2',3'-didehydro-2',3'-dideoxyuridines were synthesized and evaluated for their in vitro inhibitory activity against M. bovis and M. avium. 5-(C-1 Substituted)-2'-deoxyuridine derivatives emerged as potent inhibitors of M. avium (MIC90 = 1-5 microg/mL range). The nature of C-5 substituents in the 2'-deoxyuridine series appeared to be a determinant of anti-mycobacterial activity. This new class of inhibitors could serve as useful compounds for the design and study of new anti-tuberculosis agents.

Residential segregation and the epidemiology of infectious diseases

Several empirical studies have documented the effects of residential segregation on health inequalities between the US African-American and white populations. However, the majority of such studies have not explained the pathways that link residential segregation and specific health outcomes. This paper presents a conceptual framework of the role that residential segregation may play in the epidemiology of tuberculosis (TB) and other infectious diseases. This is an important issue given the concentration of TB cases among US racial/ethnic minorities and the increasing gap in the incidence of infectious diseases between minorities and the white majority. Segregation may have an indirect effect on the transmission of TB because of its negative impact on the quality of neighborhood environment in segregated communities. Segregation concentrates poverty, overcrowded and dilapidated housing and social disintegration in minority areas, and results in limited access to health care. Furthermore, two dimensions of residential segregation (isolation and concentration) may have direct effects on TB transmission. The isolation of minorities confines TB to segregated areas and prevents transmission to the rest of the population. High-density levels in minority areas increase the probability of transmission within the segregated group. In order to operationalize the above pathways, health researchers may rely on the segregation literature, which has conceptualized various dimensions of residential segregation and proposed ways to measure them. The indirect pathways that link segregation and TB can be captured through exposure indices, which quantify the concentration of risk factors for TB for various racial and ethnic groups. The direct pathways can be captured through the isolation index (which is a proxy for the degree of interaction between the segregated group and the rest of the population) and two proposed measures of density (which are proxies for the likelihood of transmission within the segregated group and from the segregated group to the rest of the population).

Directly observed therapy for the treatment of tuberculosis--evidence based dosage guidelines

Tuberculosis is a communicable disease with public health implications and effective treatment is essential for control of the disease and prevention of the emergence of drug resistant strains. Drug therapy for this disease is well established and discussion now surrounds frequency of administration, duration of treatment and methods of improving compliance. Directly observed intermittent therapy of tuberculosis is supported by the World Health Authority and has become the standard of care in the U.S.A. Available dosage guidelines for directly observed therapy are only supported by limited data. A literature review of recent studies with clinical outcome measures was conducted. Following this review evidence based guidelines have been produced.

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.

Population pharmacokinetic modeling of isoniazid, rifampin, and pyrazinamide

Isoniazid (INH), rifampin (RIF), and pyrazinamide (PZA) are the most important drugs for the treatment of tuberculosis (TB). The pharmacokinetics of all three drugs in the plasma of 24 healthy males were studied as part of a randomized cross-over phase I study of two dosage forms. Subjects ingested single doses of INH at 250 mg, RIF at 600 mg, and PZA at 1,500 mg. Plasma was collected for 36 h and was assayed by high-performance liquid chromatography. The data were analyzed by noncompartmental, iterative two-stage maximum a posteriori probability Bayesian (IT2B) and nonparametric expectation maximization (NPEM) population modeling methods. Fast and slow acetylators of INH had median peak concentrations in plasma (C[max]) of 2.44 and 3.64 microg/ml, respectively, both of which occurred at 1.0 h postdose (time of maximum concentrations of drugs in plasma [T(max)]), with median elimination half-lives (t1/2) of 1.2 and 3.3 h, respectively (by the NPEM method). RIF produced a median C(max) of 11.80 microg/ml, a T(max) of 1.0 h, and a t1/2 of 3.4 h. PZA produced a median C(max) of 28.80 microg/ml, a T(max) of 1.0 h, and a t1/2 of 10.0 h. The pharmacokinetic behaviors of INH, RIF, and PZA were well described by the three methods used. These models can serve as benchmarks for comparison with models for other populations, such as patients with TB or TB with AIDS.

Tuberculosis in a young baseball player

This report of a 19-year-old pitcher with chest pain illustrates how an atypical presentation of pulmonary tuberculosis in an athlete can delay diagnosis. In addition to a history, physical examination, and chest radiographs, the tuberculin skin test is the key to diagnosis of this disease. Laboratory work includes blood tests, liver and renal function studies, analysis of aspirated fluids, and sputum cultures. Treatment generally consists of daily doses of isoniazid, rifampin, pyrazinamide, and ethambutol or streptomycin. Screening close contacts such as teammates is essential; prophylaxis using isoniazid must be initiated for those who test positive.

Nontuberculous mycobacterial infections

OBJECTIVE

To review the epidemiology, clinical manifestations, diagnosis, and treatment of nontuberculous mycobacterial infections other than Mycobacterium avium complex (MAC).

DATA SOURCES

A MEDLINE search of English-language literature pertaining to nontuberculous mycobacteria other than MAC was performed. Additional literature was obtained from reference lists of pertinent articles identified through the search.

STUDY SELECTION AND DATA EXTRACTION

All articles were considered for possible inclusion in the review. Information judged by the author to be pertinent was selected for discussion.

DATA SYNTHESIS

Mycobacterial infections, including those caused by nontuberculous mycobacteria other than MAC, have assumed greater importance over the past decade, due in part to the changing spectrum of immunosuppression as manifested by organ transplantation and HIV infection. Many pathogenic nontuberculous mycobacteria have been identified that are associated with a wide variety of localized, organ-specific, and systemic infections. Of concern, these organisms exhibit variable, species-specific susceptibility to traditional antimycobacterial drugs and other antimicrobials. In addition, long treatment courses and adjunctive surgical therapy are often required to effect cure. Important antimicrobials for the management of these infections include cefoxitin, imipenem/cilastatin, aminoglycosides (other than streptomycin), tetracyclines, macrolides, and trimethoprim/sulfamethoxazole, as well as traditional antimycobacterials.

CONCLUSIONS

Nontuberculous mycobacteria have assumed an increasing role in disease etiology in both nonimmunocompromised and immunocompromised individuals. Advent of rapid diagnostic techniques and susceptibility testing has allowed the clinician to identify these organisms and initiate effective treatment on a more timely basis with an improved chance for cure. Few therapeutic agents are available for treatment of these infections, many of which are not considered classic antimycobacterials.

Recent advances: antiinfectives

OBJECTIVE

To update readers on the significant changes in infectious diseases pharmacotherapy.

DATA SOURCES

An Index Medicus and Iowa Drug Information Service search (1993-1994) of English-language literature pertaining to the selected topic areas was performed. Additional information from abstracts presented at scientific meetings were identified by the authors.

STUDY SELECTION AND DATA EXTRACTION

All identified studies were screened and those judged relevant to the update were evaluated.

DATA SYNTHESIS

New or clinically significant data since 1992 that related to peptic ulcer disease, microbial resistance (e.g., Enterococcus spp., Streptococcus pneumoniae, Mycobacterium tuberculosis, Candida albicans), immunomodulators, and AIDS were evaluated and compared with previous data.

CONCLUSIONS

There have been several exciting and significant changes in infectious diseases pharmacotherapy evident from this review.

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.