Treatment of Active Tuberculosis: Challenges and Prospects

Clin Chest Med 26 (2005) 273 – 282 Treatment of Active Tuberculosis: Challenges and Prospects Behzad Sahbazian, DOa, Stephen E. Weis, DOb,* a John Peter Smith Hospital, Viola Pitts/Como Community Health Clinic, 4701 Bryant Irvin Road, Fort Worth, TX 76107, USA b Department of Medicine, University of North Texas Science Center, Texas College of Osteopathic Medicine, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA In the past 5 years, the Tuberculosis Trials Consortium (TBTC) of the Centers for Disease Control and Prevention has completed several large studies that have improved the understanding of pharmacotherapy of tuberculosis. Insights gained from these studies have resulted in major changes in drug therapy of tuberculosis in HIV-infected and noninfected individuals [1 – 5]. These advances require that tuberculosis drug therapy now be individualized. Recommended treatment regimens are based on a patient’s risk profile that is determined by a combination of hematologic, microbiologic, clinical, and radiographic findings [6]. These studies have resulted in substantial changes in the treatment guidelines. Although they are more complicated than the previous guidelines, they allow treatment to be refined so that it can be extended in patients at high risk for treatment failure and allow shorter, more convenient treatment regimens in patients who can be identified as being at very low risk for failure [2]. This article reviews the basic principles of drug treatment of tuberculosis, individual pharmacologic agents, current treatment recommendations, and several special situations that clinicians are likely to encounter in medical practice. Axioms of chemotherapy of tuberculosis Effective tuberculosis drug therapy requires not one but at least two effective drugs. This axiom * Corresponding author. E-mail address: [email protected] (S.E. Weis). emerged from the first studies of drug therapy of tuberculosis initiated in the late 1940s. These studies evaluated monotherapy with streptomycin and subsequently para-aminosalicylic acid (PAS) [7 – 9]. They demonstrated that drug resistance developed frequently in persons treated with monotherapy. During 3 months of monotherapy with streptomycin, 92% of persons who remained culture-positive developed streptomycin resistance [3]. Resistance also developed commonly during monotherapy with PAS and was found in approximately one third of patients during 4 months of treatment [9]. It was also observed that resistance was much less common in persons treated with the combination of streptomycin and PAS, and that many more patients treated with the two-drug regimen became bacteriologically negative with 4 months of therapy [9]. Ten percent or less of persons treated simultaneously with streptomycin and PAS developed streptomycin resistance [7,8]. It also was observed that development of resistance was associated with a worse prognosis and with more severe disease [3]. From these early observations came the principle that tuberculosis treatment must include simultaneous treatment with at least two effective drugs. The microbiologic basis for these early observations was not identified until the early 1960s and remains as important today to understand the design of current treatment regimens [10]. Persons with cavitary disease are estimated to have bacterial populations of approximately 108 organisms in each cavity [10,11]. During division, Mycobacterium tuberculosis bacilli mutate from drug-susceptible to drugresistant status spontaneously, randomly, and at a predictable rate [12]. The proportion of naturally oc- 0272-5231/05/$ – see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.ccm.2005.02.011 chestmed.theclinics.com 274 sahbazian curring organisms that are resistant to antituberculosis drugs is variable, approximately 10 5 for ethambutol, 10 6 for isoniazid and streptomycin, and 10 8 for rifampin [8]. The probability of a single organism mutating simultaneously and becoming resistant to two drugs is the product of individual probabilities of mutation. It can therefore be estimated that the likelihood of an organism having mutations simultaneously for isoniazid and rifampin is approximately [(1  10 6)  (1  10 8)] or (1  10 14), and the bacillary burden in human tuberculosis is several orders less than this [13]. This mutation rate is the basis for the observation that successful drug therapy requires that at least two drugs be given concurrently to prevent selection of drug-resistant organisms. If a single drug is used for treatment, selection of the resistant organisms occurs, and the patient rapidly becomes resistant to that drug. This mutation rate is also the basis for designing regimens with an intensive initial phase that uses more medications and a less intense continuation phase that uses fewer medications. Corollaries of the treatment axiom that tuberculosis treatment must include simultaneous treatment with at least two effective drugs are important for designing effective tuberculosis regimens and tuberculosis control programs. Because of the possibility of resistance, a single drug is never added to a failing drug-treatment regimen. Optimal design of re-treatment regimens should include at least two medications to which the patient is naı̈ve, and clinicians designing initial treatment regimens must consider prevailing tuberculosis-susceptibility patterns in the community where the infection probably was acquired. It is equally important to successful treatment that the patient actually take the two probably effective drugs. The only way to ensure that a patient actually takes drug therapy as prescribed is direct observation of therapy. If three separate drugs are prescribed for a patient with tuberculosis, the patient may, for many reasons, take a single drug at a time. Short-term single-drug therapy in a person with high bacillary burden can lead to emergence of drug resistance [7 – 9]. If a patient happens to be initially resistant to one drug and takes a combination of two drugs, including the one to which he or she is resistant, drug resistance to the second drug will emerge. Similarly, if the patient is resistant to two drugs and takes these two drugs and a single effective drug, resistance to the third will emerge. Therefore, poor adherence, inadequate prescribing, or both may result in the development of multidrug resistance. Although these axioms may seem selfevident, the growing number of persons worldwide & weis with drug-resistant tuberculosis is testimony that these principles are not being implemented successfully [14]. The last 50 years of tuberculosis drug treatment can be summarized succinctly. First, it was demonstrated that proper chemotherapy and the cooperation of the patient are the most important factors influencing response to treatment [15]. Second, it has been proven that the social factors such as those corrected during sanatoria treatment of tuberculosis (which provided bed rest, airy accommodations, a well-balanced diet, good nursing care, and psychologic balance) have had no effect on outcome in persons prescribed drug therapy and cooperating with treatment [15]. Third, a few new antituberculosis drugs have been developed. For the most part, however, progress has been made in learning to use available drugs more effectively, with treatment regimens becoming refined to the current treatments that are shorter, have fewer side effects, and are more convenient [6]. Pharmacology and toxicity of antimycobacterial agents The current drugs approved by the Food and Drug Administration (FDA) for the treatment of tuberculosis include isoniazid, pyrazinamide, rifampin, rifapentine, ethambutol, cycloserine, ethionamide, capreomycin, PAS, and streptomycin. Drugs that commonly are recommended by expert panels for use in the treatment of tuberculosis but are not FDA approved include rifabutin, the aminoglycosides including amikacin, kanamycin, and the fluoroquinolones including ciprofloxacin, moxifloxacin, and levofloxacin. Of the approved drugs, isoniazid, rifampin, ethambutol, and pyrazinamide are considered first-line antituberculosis drugs. Rifapentine and rifabutin can also be considered first-line drugs under special conditions discussed later. The others are categorized as second-line drugs, which are used when the first-line drugs are unsuitable because of drug intolerance or infection with drug-resistant tuberculosis. Additionally clarithromycin, amoxicillin/clavulanate, and linezolid have been used in the treatment of patients with drug-resistant tuberculosis. Drug-level monitoring is not routinely an important aspect of treatment in a patient with active tuberculosis. Therapeutic drug monitoring is most useful when there is a direct relationship between serum concentrations and therapeutic response and when serum concentrations serve as a surrogate for drug concentrations at the site of action. Therapeutic treatment of active tuberculosis drug monitoring is also important when there is a narrow range of concentrations that are effective and safe and when toxicity or lack of effectiveness puts the patient at great risk [16,17]. Examples of situations in which therapeutic drug monitoring is useful for safety include persons treated with aminoglycosides and persons treated with ethambutol or cycloserine with renal impairment. Isoniazid Isoniazid is used for the treatment of both latent and active tuberculosis and works primarily by inhibiting cell wall synthesis. It is usually administered orally but has been given successfully intramuscularly or intravenously [6]. Isoniazid is cleared predominantly through the liver by acetylation. A patient’s acetylation status and the associated differences in plasma isoniazid concentrations are not associated with isoniazid-induced liver injury [18]. Additionally, no association was found between plasma isoniazid concentrations and isoniazid-induced liver injury [19]. Isoniazid is distributed throughout the body with peak concentrations occurring within 1 to 2 hours after the administration of an oral dose [20]. The usual dose for isoniazid is 3 to 5 mg/kg body weight/day in adults with a maximum dose of 300 mg/day [6]. Isoniazid generally is well tolerated. Hepatic side effects are perhaps the best known of the untoward effects associated with isoniazid use. Less well known is the asymptomatic elevation of liver aminotransferases of up to five times the upper limits of normal, which occurs in approximately 20% of patients receiving isoniazid. This asymptomatic mild elevation of liver aminotransferases is not progressive, is not an indication of progressive liver toxicity, and when asymptomatic does not require discontinuation of isoniazid treatment [6]. Isoniazid-induced hepatitis does occur, but recent studies indicate it is less common than previously thought. Isoniazidinduced hepatitis is estimated to occur in 0.15% of those starting and in 0.15% of those completing treatment for latent tuberculosis infection [21]. The rate of isoniazid-induced hepatitis is higher when isoniazid is combined with rifampin [22]. It is also more common in older persons, heavy alcohol consumers, and persons with underlying liver disease [23]. Based on a large survey, the risk of isoniazidinduced fatal hepatitis is much lower than previously thought—0.001%—when patients are monitored routinely for liver toxicity [24,25]. The risk increases slightly in patients over the age of 35 years. 275 Peripheral neuropathy also is associated occasionally with use of isoniazid. Neuropathy occurs more commonly among persons who have other risks for neuropathy. Persons at increased risk of peripheral neuropathy include those who are nutritionally deficient, alcoholics, diabetics, pregnant women, breastfeeding mothers, and patients with renal disease. Vitamin B6 (pyridoxine) supplements usually are given with isoniazid to prevent development of peripheral neuropathy [6]. Hypersensitivity reactions including arthralgias, irritability, seizures, and lupuslike syndrome have also been reported in patients receiving isoniazid. Although as many as 20% of patients treated with isoniazid develop a positive antinuclear antibody test, systemic lupus rarely occurs [26]. Isoniazid has clinically important reactions with other concomitantly used medications. Isoniazid can affect the levels of certain antiseizure medications, such as phenytoin and carbamazepine. Levels of these medications must be monitored during isoniazid therapy [6]. Rifamycins The rifamycins, which include rifampin, rifabutin, and rifapentine, work by interfering with RNA synthesis, even in bacilli with minimal metabolic activity [27]. The rifamycins are variable inducers of the cytochrome P450 system. Rifampin, rifabutin, and rifapentine are each first-line drugs for the treatment of tuberculosis in different circumstances. Rifampin generally is given orally, but formulations are available for parenteral therapy. The usual dose for rifampin in adults is 10 mg/kg to a maximum of 600 mg daily. It is distributed well throughout the body and reaches effective concentrations in all tissues [6]. Rifampin is a necessary component of all short-course regimens [6]. Rifampin is generally a well-tolerated drug. The most common side effect of rifampin use is an orange discoloration of the urine, tears, and other body fluids. The change in the color of the urine or other body fluids can be disconcerting to persons treated with rifampin if they are not warned. This discoloration has been associated with discoloration of soft contact lenses and clothing. This staining must be rare, however, because the author and colleagues have treated many contact lens wearers with rifampin and never have had a complaint of discoloration of contacts lens, even though they routinely warn patients of this potential side effect. Rifampin can also cause pruritus [28]. Gastroin- 276 sahbazian testinal upset, including diarrhea, nausea, and abdominal pains, can occur but rarely require drug discontinuation and are usually self limiting [29]. Transient elevation of serum bilirubin may be observed during rifampin administration. Hepatitis is more common when rifampin is administered with isoniazid [30]. A more serious side effect of rifampin use is an influenzalike syndrome. Symptoms often mistaken by patients and physicians for influenza, including fevers, chills, faintness, headaches, myalgia, and arthralgia, occur alone or in combination. This hypersensitivity syndrome seems to be immune mediated and develops primarily when rifampin is given intermittently or in larger doses than are currently recommended. It most commonly develops after 3 to 6 months but can occur at any time during treatment [31]. Among persons receiving once-weekly rifampin as part of the antituberculosis regimen, 35% to 57% of persons who received 1200 to 1800 mg rifampin developed a flulike syndrome; the rates were 22% to 31% among those receiving 900 mg/week and 10% among persons taking 600 mg/week [32]. In contrast, for persons who received twice-weekly rifampin, a flulike syndrome was reported in 8% of those receiving 900 mg/week and in 4% of those receiving 600 mg/week. Symptoms usually appear 1 to 2 hours after administration of the drug and last up to 8 hours [31,32]. The hypersensitivity syndrome can be accompanied by other manifestations that may be severe and, rarely, life threatening. The incidence of individual adverse drug reactions included in the hypersensitivity syndrome is not well described for persons treated for tuberculosis. A study of 20,667 patients treated for leprosy with rifampin, 600 mg/day for 3 months, noted the following incidence rates: rash (0.07%), acute renal failure (0.1%), thrombocytopenia (0.01%), and hypotension (0.01%) [33]. Rifabutin use is also associated with rare immune-related reactions. These reactions tend to be hematologic, such as leukopenia and thrombocytopenia [33,34]. Rifampin can interact with a large number of medications because it is a potent inducer of several enzymes. Rifampin induction of hepatic enzymes can reduce serum concentrations of oral contraceptives, resulting in pregnancy, and women relying on hormonal methods of contraception need to use additional means of contraception. Rifampin can increase the metabolism of methadone and glucocorticoids, resulting in narcotic withdrawal syndrome and adrenal insufficiency or exacerbation of the illness being treated by glucocorticoid. The interactions of rifampin with other drugs are so extensive that all & weis concurrent medications must be checked for interactions with rifampin. Ethambutol Ethambutol is used in combination with isoniazid and rifampin in the initial treatment of active tuberculosis and has been proven effective in primary treatment of pulmonary tuberculosis [35]. Ethambutol is used with isoniazid and rifampin to prevent selecting resistant organisms when resistance to one of the primary drugs is present. Like isoniazid, ethambutol inhibits cell wall synthesis. It is available only in the oral form. Because it is secreted through the kidneys, it can accumulate in patients with renal insufficiency. The usual dose for ethambutol is 15 to 20 mg/kg/day or 50 mg/kg two times per week. Ethambutol generally is very well tolerated, but, rarely, it can cause retrobulbar neuritis. This syndrome first manifests as decreased red-green color discrimination and visual acuity. Although it can result in irreversible vision loss, recognition of the symptoms and prompt discontinuation of the drug usually results in return of normal vision. Reducing the dose of ethambutol to 15 mg/kg/day can minimize the risk [36]. Fluoroquinolones Levofloxacin, moxifloxacin, and gatifloxacin all are active against mycobacterium tuberculosis [37,38]. Although they are not approved by the FDA for the treatment of tuberculosis, they are used frequently in treating drug-resistant tuberculosis or when patients are intolerant of first-line agents [39,40]. The adult dose for levofloxacin is 500 to 1000 mg/day orally. Moxifloxacin is administered at 400 mg/day. Central nervous system (CNS) concentrations of fluoroquinolones have been found to be around 16% to 20% of serum after administration of a standard dose of levofloxacin [41]. Microbial resistance to fluoroquinolones is common in the community setting; therefore it is imperative that fluoroquinolones be used only when appropriate. The most common side effects reported with the use of this group of antimicrobials are gastrointestinal symptoms such as nausea, anorexia, dyspepsia, abdominal pain, followed by CNS disturbances (headache, dizziness, drowsiness, abnormal vision) and liver enzyme abnormalities [42]. Fluoroquinolones were not developed with the expectation that they would be used for months; however most experts in the field of TB have reported a good safety profile and tolerability with long-term use. Controlled stud- treatment of active tuberculosis ies are in progress by CDC/TBTC to look at fluoroquinolones as there is a dearth of information on the efficacy of long-term fluoroquinolone treatment (either daily or intermittently) as is required for multidrug resistant TB. Pyrazinamide Pyrazinamide is the primary drug used in the initial intensive phase of active tuberculosis therapy to reduce the total length of therapy. It has a sterilizing effect and helps eliminate potential persisters and consequently is used in the first two months of intensive therapy to reduce the total length of therapy [43]. It is administered orally and is first broken down by the liver. The remaining metabolites are excreted through the kidney [44]. It is more hepatotoxic than isoniazid; therefore, liver function tests should be monitored. It can exacerbate gout and arthralgias by elevating serum uric acid levels [45]. The adult dose for pyrazinamide, based on estimated lean body weight, is 25 mg/kg for daily oral administration orally, 37.5 mg/kg for trice-weekly administration, and 50 mg/kg for twice-weekly administration [6]. Aminoglycosides Amikacin [46], kanamycin [47], and capreomycin are three aminoglycosides that are second-line agents used in treatment of patients who have resistant tuberculosis. They are available for both intramuscular and intravenous administration. All three are administered at 15 mg/kg/day (maximum, 1.0 g/day). Sensitivity tests have shown incomplete crossresistance between amikacin and capreomycin but complete cross-resistance between amikacin and kanamycin [48]. Adverse effects most commonly associated with the use of these drugs are ototoxicity and nephrotoxicity. Patients receiving these medications should have regular audiograms, vestibular and Romberg testing, and monitoring of renal function. Treatment guidelines Tuberculosis treatment guidelines for the United States have been prepared by and endorsed by the American Thoracic Society, the Infectious Diseases Society of America, and the Centers for Disease Control and Prevention. These regimens are, for the most part, evidence based. These guidelines rate treatments according to the strength of the evidence supporting their use, using a system developed by the 277 Box 1. Infectious Diseases Society of America/United States Public Health Service rating system for treatment recommendations based on quality of evidence Strength of the recommendation A. Preferred; should generally be offered B. Alternative; acceptable to offer C. Offer when preferred or alternative regimens cannot be given D. Should generally not be offered E. Should never be offered Quality of evidence supporting the recommendation I. At least one properly randomized trial with clinical end points II. Clinical trials that either were not randomized or were conducted in other populations III. Expert opinion From Gross PA, Barrett TL, Dellinger EP, et al. Purpose of quality standards for infectious diseases. Infectious Diseases Society of America. Clin Infect Dis 1994;18: 421; with permission. United States Public Health Service and the Infectious Diseases Society of America (Box 1) [6]. The guidelines recommend four regimens for treating persons with drug-susceptible tuberculosis [6]. These regimens contain recommendations for regimen modification under circumstances determined by a combination of hematologic, microbiologic, clinical, and radiographic findings [6]. Each regimen has an initial intensive phase of 2 months followed by several options for the continuation phase of 4 or 7 months’ duration. These regimens, together with the number of doses specified by the regimen, are described in Table 1. The initial phases are denoted by a number (1, 2, 3, or 4), and the continuation phases associated with the initial phase are denoted by the number of the initial phase plus a letter designation for the continuation phase (a, b, or c). The continuation phase can be given daily, two times per week, or three times per week with iso- 278 Table 1 Drug regimens for culture-positive pulmonary tuberculosis caused by drug-susceptible organisms Initial phase Continuation phase Regimen Drugs Interval and dosesc,d (minimal duration) 1 INH RIF PZA EMB INH RIF PZA EMB INH RIF PZA EMB INH RIF EMB 7 d/wk for 56 doses (8 wk) or 5 d/wk for 40 doses (8 wk)e 1a INH/RIF 1b 1cg 2a 2bg INH/RIF INH/RPT INH/RIF INH/RPT 7 d/wk for 128 doses (18 wk) or 5 d/wk for 90 doses (18 wk)c 2/wk for 36 doses (18 wk) 1/wk for 18 doses (18 wk) 2/wk for 36 doses (18 wk) 1/wk for 18 doses (18 wk) 3a INH/RIF 3/wk for 54 doses (18 wk) 4a INH/RIF 4b INH/RIF 7 d/wk for 217 doses (31 wk) or 5 d/wk for 156 doses (31 wk)c 2/wk for 62 doses (31 wk) 2 3 4 7 d/wk for 14 doses (2 wk), then 2/wk for 12 doses (6 wk) or 5 d/wk for 10 doses (2 wk)e then 2/wk for 12 doses (8 wk) 3/wk for 24 doses (8 wk) 7 d/wk for 56 doses (8 wk) or 5 d/wk for 40 doses (8 wk)e Range of total doses (minimal duration) HIV HIV+ A (I) A (II) A (I) B (I) A (II) B (I) A (II)f E (I) B (II)f E (I) B (I) B (II) 273 – 195 (39 wk) C (I) C (II) 118 – 102 (39 wk) C (I) C (II) 182 – 130 (26 wk) 92 – 76 74 – 68 62 – 68 44 – 40 (26 (26 (26 (26 wk) wk) wk) wk) 78 (26 wk) Abbreviations: EMB, Ethambutol; HIV , HIV-negative; HIV+, HIV-positive; INH, isoniazid; PZA, pyrazinamide; RIF, rifampin; RPT, rifapentine. a Definitions of evidence ratings: A, preferred; B, acceptable alternative; C, offer when A and B cannot be given; E, should never be given. b Definitions of evidence ratings: I, randomized clinical trial; II, data from clinical trials that were not randomized or were conducted in other populations; III, expert opinion. c When directly observed therapy is used, drugs may be given 5 d/wk and the necessary number of doses adjuated accordingly. Although there are no studies that compare five with seven daily doses, extensive experience indicates this would be an effective practice. d Patients with cavitation on initial chest radiograph and positive cultures at completion of 2 months of therapy should receive a 7-month (31 wk; either 217 doses [7/wk] or 62 doses [2/wk]) continuation phase. e Five d/wk administration is always given by DOT. Rating for 5 d/wk regimens is A III. f Not recommended for HIV-infected patients with CD4+ cell counts <100 cells/ml. g Options 1c and 2b should be used only in HIV-negative patients who have negative sputum smears at the time of completion of 2 months of therapy and who do not have cavitation on initial chest radiograph (see text). For patients started on this regimen and found to have a positive culture from 2-month specimen, treatment should be extended an extra 3 months. From American Thoracic Society, Centers for Disease Control and Prevention, and Infectious Diseases Society of America. Treatment of tuberculosis. MMWR Recomm Rep 2003; 52(RR-11):3. weis Interval and dosesc (minimal duration) & Drugs sahbazian Regimen Ratinga (evidence)b treatment of active tuberculosis niazid and rifampin. It can also be given, more conveniently for patients and staff, once weekly using isoniazid and rifapentine in patients with tuberculosis without cavitation on the chest radiograph. This group is estimated to represent 40% of persons with tuberculosis in the United States [3]. Persons who have cavitation on the initial or follow-up chest radiograph or who are culture positive at the end of initial phase of therapy (usually completed after 2 months) have an unacceptably high risk of treatment failure [3,6]. For these patients, the continuation phase should be extended for an additional 3 months [6]. It is critically important to have sputum cultures at the time of completion of the initial phase of treatment to identify patients at increased risk of relapse. The treatment of tuberculosis in persons with HIV is discussed elsewhere in this issue. Treatment of tuberculosis may be delayed for many reasons. The current treatment guidelines defined completion of adequate therapy by the number of doses ingested as well as by the duration of treatment administration [6]. The minimum goal for adequate therapy is delivery of the full number of doses in no more than 150% of the expected delivery duration [6]. Special situations Central nervous system tuberculosis is one of the most devastating presentations of human tuberculosis. Disability and death occur despite antituberculosis therapy [49]. The best antimicrobial agents for the treatment of central nervous system tuberculosis have not been validated by well-designed, randomized, clinical trials. Isoniazid and pyrazinamide penetrate the meninges in all stages of inflammation. Rifampin, ethambutol, and aminoglycosides penetrate the blood – brain barrier in the presence of meningeal inflammation but poorly in its absence. The use of glucocorticoids in an attempt to reduce mortality and morbidity has been controversial [50]. Recently, a large trial of dexamethasone adjunct therapy for persons 14 years of age and older with tuberculous meningitis has clarified the role of glucocorticoids [51]. Dexamethasone treatment was started as soon as possible after starting antituberculosis treatment. Patients were stratified by Glasgow Coma Scale and given intravenous dexamethasone for 4 weeks for severe disease and for 2 weeks for mild disease. Subsequently, all patients were given tapering doses of dexamethasone orally for an additional 4 weeks. Dexamethasone adjunctive treatment improved survival. Adverse and severe adverse events were reduced significantly in the dexamethasone- 279 therapy group. There was no demonstrable improvement in the broader prespecified combined end points of death or severe disability after 9 months [52]. There have been many reports of an increased risk of tuberculosis in patients receiving tumor necrosis factor- alpha (TNF-a) antagonists [53,54]. These agents, which include infliximab, etanercept, and adalimumab, are used for the treatment of an expanding group of diseases and work by blocking TNF-a; an inflammatory cytokine. TNF-a is expressed by activating macrophages, T cells, and other immune cells and is an important part of the host response against M. tuberculosis and other intracellular organisms. Current expert opinion on this emerging problem in tuberculosis treatment is that the TNF-a antagonist should be discontinued if tuberculosis develops during TNF-a antagonist therapy. The optimal time for resuming TNF-a antagonist therapy is undetermined. It is recommended that TNF-a antagonist therapy be withheld at least until treatment with the tuberculosis regimen has been started, and the patient’s condition has improved [54]. Tuberculosis occurring in pregnancy is a danger to the pregnant woman and her child, and treatment should not be delayed because of the pregnancy. Infants born to women with untreated tuberculosis may be of lower birth weight than those born to women without tuberculosis and can acquire congenital tuberculosis [55 – 57]. Of the first-line medications, pyrazinamide is not recommended for general use in pregnant women in the United States because of insufficient data to determine safety. Aminoglycosides should not be used to treat tuberculosis in pregnancy, because they are associated with birth defects [6]. There is little information about the safety of second-line antituberculosis drugs during pregnancy. The recommended initial treatment regimen in pregnancy should consist of isoniazid, rifampin, and ethambutol [6]. If the organism is confirmed to be susceptible to isoniazid and rifampin, the ethambutol may be discontinued and isoniazid and rifampin continued for a minimum of 9 months [6]. It is recommended that pregnant women receiving isoniazid also be given pyridoxine (25 mg/day) [6]. Breastfeeding should not be discouraged for women being treated with first-line agents, because the small concentrations of these drugs in breast milk do not produce toxic effects in the nursing infant [58]. Renal insufficiency increases the risk for developing tuberculosis, and treatment of the two conditions concurrently is a complex and common situation. Isoniazid and rifampin are metabolized in the liver, and dosages need not be changed in persons with chronic renal failure [59 – 61]. Metabolites of 280 sahbazian pyrazinamide are excreted renally and can accumulate in patients with renal insufficiency [61]. Approximately 80% of ethambutol is cleared by the kidneys, so ethambutol may accumulate in patients with renal insufficiency [59,61]. Reducing the dosage may avoid toxicity, but the peak serum concentrations achieved may be too low to be effective. Therefore increasing the dosing interval is recommended [60]. For patients undergoing hemodialysis, administering all drugs for tuberculosis after dialysis is a way to facilitate directly observed treatment and simultaneously to avoid removal of drugs such as pyrazinamide [6]. To avoid toxicity, it is important to monitor serum drug concentrations in persons with renal failure who are taking aminoglycosides, cycloserine, or ethambutol [60]. Data are unavailable for the effect of peritoneal dialysis on the clearance of antituberculosis drugs. The challenges facing patients with tuberculosis and underlying liver disease are great. Clinicians must choose antituberculosis agents that, with a few exceptions, are metabolized by the liver and can potentially cause additional liver damage [62 – 64]. This damage can be life threatening for a person with marginal hepatic function [62 – 65]. Hepatic dysfunction can also alter absorption and distribution of drugs that are metabolized or excreted by the liver [65]. In the setting of severe liver disease, it is reasonable to include fewer hepatotoxic medications and to extend the period of treatment [6,65]. This change can be accomplished using a single hepatotoxic drug, generally rifampin, in combination with ethambutol, a quinolone, and an aminoglycoside. Isoniazid can be substituted for rifampin, if rifampin cannot be given [6]. For these complicated patients, expert opinion should be obtained [6]. Summary Insights gained from studies done by the TBTC have resulted in major changes in the recommendations for drug therapy of tuberculosis in HIV-infected and noninfected individuals [1 – 5]. Although the goals for the treatment of tuberculosis remain the same, these advances require that tuberculosis drug therapy now be more individualized. Treatment regimens are based on a patient’s risk profile based on a combination of hematologic, microbiologic, clinical, and radiographic findings [6]. Although they are more complicated than the previous guidelines, they allow treatment to be refined so that it can be extended in patients at high risk for treatment failure and allow shorter, more convenient treatment regi- & weis mens in patients who can be identified as being at very low risk for failure [2]. Acknowledgments The authors acknowledge Thaddeus Miller’s work in editing this article. References [1] Vernon A, Burman W, Benator D, et al. Relapse with rifamycin mono-resistant tuberculosis in HIV-infected patients treated with supervised once-weekly rifapentine and isoniazid. Lancet 1999;353:1843 – 7. [2] Centers for Disease Control and Prevention. Acquired rifamycin resistance in persons with advanced HIV disease being treated for active tuberculosis with intermittent rifamycin-based regimens. MMWR Morb Mortal Wkly Rep 2002;51:214 – 5. [3] Benator D, Bhattacharya M, Bozeman L, et al. Tuberculosis Trials Consortium. Rifapentine and isoniazid once a week versus rifampicin and isoniazid twice a week for treatment of drug-susceptible pulmonary tuberculosis in HIV-negative patients: a randomised clinical trial. Lancet 2002;360:528 – 34. [4] Weiner M, Burman W, Vernon A, et al. Tuberculosis Trials Consortium. Low isoniazid concentrations and outcome of tuberculosis treatment with once-weekly isoniazid and rifapentine. Am J Respir Crit Care Med 2003;167:1341 – 7. [5] Weiner M, Bock N, Peloquin CA. 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