Somoskovi A, Dormandy J, Mitsani D, Rivenburg J, Salfinger M.
J Clin Microbiol. 2006 Oct 11; [
Isoniazid (INH) and rifampin (RIF) are two of the most important antituberculosis drugs, and resistance to both can often result in treatment failure and fatal clinical outcome. Resistance to these two first-line drugs is most often attributed to mutations in the katG, inhA, and rpoB genes. Historically, the identification and susceptibility testing of Mycobacterium tuberculosis complex (MTBC) takes weeks to complete. Rapid detection of resistance using the PCR-based Genotype MTBDR assay (Hain Lifescience GmbH, Nehren, Germany) has the potential to significantly shorten the turnaround time from specimen receipt to reporting of susceptibility testing results. Therefore, the aim of the present study was to determine (1) the sensitivity and accuracy of the Genotype MTBDR assay for the detection of MTBC, and (2) the ability of the assay to detect the presence of INH and RIF resistance-associated mutations in katG and rpoB from samples taken directly from smear-positive clinical specimens. The results were compared with those obtained with the reference BACTEC 460TB system, combined with standard DNA sequencing analysis methods for katG, inhA and rpoB. A total of 92 drug resistant and 51 pan-susceptible smear-positive specimens were included in the study. The Genotype MTBDR assay accurately and rapidly detected MTBC in 94.4% of the 143 specimens and showed a sensitivity of 94.4% for katG and 90.9% for rpoB, when used directly on smear-positive specimens. The assay correctly identified INH resistance in 48 (84.2%) of the 57 specimens containing strains with resistance to high level of INH (0.4 microg/ml), and RIF resistance in 25 (96.2%) of the 26 specimens containing RIF-resistant strains.
Rifapentine is a recently approved antituberculosis drug that has not yet been widely used in clinical settings. Clinical data support intermittent use of rifapentine with isoniazid during the continuation phase of tuberculosis treatment. Patients with culture-positive, noncavitary, pulmonary tuberculosis whose sputum smear is negative for acid-fast bacilli at the end of the 2-month intensive treatment phase are eligible for rifapentine therapy. Rifapentine should not be used in human immunodeficiency virus-infected patients, given their increased risk of developing rifampin resistance with currently recommended dosages. Rifapentine is not currently recommended for children aged less than 12 years, pregnant or lactating women, or individuals with culture-negative or extrapulmonary tuberculosis. Rifapentine (600 mg) is administered once weekly with isoniazid (900 mg) during the continuation phase of treatment. This combination should only be given under direct observation. As with rifampin, drug-drug interactions are common, and regular patient monitoring is required. Ease of administration makes this regimen attractive both for tuberculosis-control programs and for patients.
Saukkonen JJ, Cohn DL, Jasmer RM, Schenker S, Jereb JA, Nolan CM, Peloquin CA, Gordin FM, Nunes D, Strader DB, Bernardo J, Venkataramanan R, Sterling TR; ATS (American Thoracic Society) Hepatotoxicity of Antituberculosis Therapy Subcommittee.
Am J Respir Crit Care Med. 2006 Oct 15;174(8):935-52.
Drug-induced liver injury (DILI) is a problem of increasing significance, but has been a long-standing concern in the treatment of tuberculosis (TB) infection. The liver has a central role in drug metabolism and detoxification, and is consequently vulnerable to injury. The pathogenesis and types of DILI are presented, ranging from hepatic adaptation to hepatocellular injury. Knowledge of the metabolism of anti-TB medications and of the mechanisms of TB DILI is incomplete. Understanding of TB DILI has been hampered by differences in study populations, definitions of hepatotoxicity, and monitoring and reporting practices. Available data regarding the incidence and severity of TB DILI overall, in selected demographic groups, and in those coinfected with HIV or hepatitis B or C virus are presented. Systematic steps for prevention and management of TB DILI are recommended. These include patient and regimen selection to optimize benefits over risks, effective staff and patient education, ready access to care for patients, good communication among providers, and judicious use of clinical and biochemical monitoring. During treatment of latent TB infection (LTBI) alanine aminotransferase (ALT) monitoring is recommended for those who chronically consume alcohol, take concomitant hepatotoxic drugs, have viral hepatitis or other preexisting liver disease or abnormal baseline ALT, have experienced prior isoniazid hepatitis, are pregnant or are within 3 months postpartum. During treatment of TB disease, in addition to these individuals, patients with HIV infection should have ALT monitoring. Some experts recommend biochemical monitoring for those older than 35 years. Treatment should be interrupted and, generally, a modified or alternative regimen used for those with ALT elevation more than three times the upper limit of normal (ULN) in the presence of hepatitis symptoms and/or jaundice, or five times the ULN in the absence of symptoms. Priorities for future studies to develop safer treatments for LTBI and for TB disease are presented.
Sekiguchi JI, Miyoshi-Akiyama T, Augustynowicz-Kopec E, Zwolska Z, Kirikae F, Toyota E, Kobayashi I, Morita K, Kudo K, Kato S, Kuratsuji T, Mori T, Kirikae T. J Clin Microbiol. 2006 Nov 15; [Epub ahead of print]
We developed DNA sequencing-based method to detect mutations in the genome of drug-resistant Mycobacterium tuberculosis. Drug resistance in M. tuberculosis is caused by mutations in restricted regions of the genome. Eight genome regions associated with drug resistance, including rpoB for rifampin (RIF), katG and the mabA (fabG1)-inhA promoter for isoniazid (INH), embB for ethambutol (EMB), pncA for pyrazinamide (PZA), rpsL and rrs for streptomycin (SM), and gyrA for levofloxacin (LVFX), were amplified simultaneously by polymerase chain reaction, and the DNA sequences were determined. It took 6.5 h to complete all procedures. Among the 138 clinical isolates tested, 55 were resistant to at least one drug. Thirty-four of 38 INH-resistant isolates (89.5%), 28 of 28 RIF-resistant isolates (100%), 15 of 18 EMB-resistant isolates (83.3%), 18 of 30 SM-resistant isolates (60%), and 17 of 17 PZA-resistant isolates (100%) had mutations related to specific drug resistance. Eighteen of these mutations had not been reported previously. These novel mutations include 1 in rpoB, 8 in katG, 1 in the mabA-inhA regulatory region, 2 in embB, 5 in pncA, and 1 in rrs. Escherichia coli expressing individually 5 of the 8 katG mutations showed loss of catalase and INH oxidation activities, and isolates carrying any of the 5 pncA mutations showed no pyrazinamidase activity, indicating that these mutations are associated with INH and PZA resistance, respectively. Our sequencing-based method was also useful for testing sputa from tuberculosis patients and for screening of mutations in M. bovis. In conclusion, our new method is useful for rapid detection of multiple drug-resistant M. tuberculosis and for identifying novel mutations in drug-resistant M. tuberculosis.