Once-weekly rifapentine-containing regimens for treatment of tuberculosis in mice

A hydrogel-based implantable multidrug antitubercular formulation outperforms oral delivery

We present a non-immunogenic, injectable, low molecular weight, amphiphilic hydrogel-based drug delivery system (TB-Gel) that can entrap a cocktail of four front-line antitubercular drugs, isoniazid, rifampicin, pyrazinamide, and ethambutol. We showed that TB-Gel is more effective than oral delivery of the combination of four drugs in reducing the mycobacterial infection in mice. Results show that half the dose of chemotherapeutic drugs is sufficient to achieve a comparable therapeutic effect to that of oral delivery.

Inhaled fixed-dose combination powders for the treatment of respiratory infections

INTRODUCTION

Respiratory infections are a major cause of morbidity and mortality. As an alternative to systemic drug administration, inhaled drug delivery can produce high drug concentrations in the lung tissue to overcome resistant bacteria. The development of inhaled fixed-dose combination powders (I-FDCs) is promising next step in this field, as it would enable simultaneous drug-drug or drug-adjuvant delivery at the site of infection, thereby promoting synergistic activity and improving patient compliance.

AREAS COVERED

This review covers the clinical and pharmaceutical rationales for the development of I-FDCs for the treatment of respiratory infections, relevant technologies for particle and powder generation, and obstacles which must be addressed to achieve regulatory approval.

EXPERT OPINION

I-FDCs have been widely successful in the treatment of asthma and chronic obstructive pulmonary disease; however, application of I-FDCs towards the treatment of respiratory infections carries additional challenges related to the high dose requirements and physicochemical characteristics of anti-infective drugs. At present, co-spray drying is an especially promising approach for the development of composite fixed-dose anti-infective particles for inhalation. Though the majority of fixed-dose research has thus far focused on the combination of multiple antibiotics, future work may shift to the additional inclusion of immunomodulatory agents or repurposed non-antibiotics.

Treatment of latent M. tuberculosis infection and use of antiretroviral therapy to prevent tuberculosis

Even with treatment of HIV with antiretroviral therapy (ART), the risk of tuberculosis (TB) reactivation remains higher in HIV-infected than HIV-uninfected persons. In this issue of the JCI, Ganatra et al. explored TB reactivation in the context of ART using TB and simian immunodeficiency virus-coinfected (TB/SIV-coinfected) nonhuman primates. The authors found that treating rhesus macaques with ART restored CD4+ T cells in whole blood, spleen, and bronchoalveolar lavage (BAL) fluid, but not in the lung interstitium. TB risk was not decreased in the coinfected macaques treated with ART for 14-63 days, suggesting that ART does not decrease the short-term risk of reactivation. Reactivation occurred as CD4+ T cells were increasing, which is consistent with observations made in humans. This study provides a potential model for systematic evaluation of TB/SIV coinfection and different treatment regimens and strategies to prevent TB reactivation.

Fully weekly antituberculosis regimen: a proof-of-concept study

BACKGROUND

The World Health Organization recommends supervising the treatment of tuberculosis. Intermittent regimens have the potential to simplify the supervision and improve compliance. Our objective was to analyse the sterilising activity of once-weekly regimens based on drugs with a long half-life, bedaquiline and rifapentine, in a murine model of tuberculosis.

METHODS

300 Swiss mice were infected intravenously infected with ×10^-6 CFU Mycobacterium tuberculosis H37Rv. Mice were treated once weekly with regimens containing: 1) bedaquiline, rifapentine and pyrazinamide (BPZ); 2) BPZ plus moxifloxacin (BPZM); 3) BPZM plus clofazimine (BPZMC); 4) the standard daily regimen of tuberculosis. All regimens were given for 4 or 6 months. Bactericidal and sterilising activity were assessed.

RESULTS

After 2 months of treatment, the mean count in lungs was 0.76±0.60 log₁₀ CFU in mice treated with the daily control regimen and negative in all mice treated with once-weekly regimens (p<0.05 compared to the daily control). All mice had negative lung cultures on completion of either 4 or 6 months of treatment, whereas 3 months after 4 and 6 months of treatment, respectively, the relapse rate was 64% and 13% in the standard daily regimen, 5% and 0% in BPZ, 0% and 0% in BPMZ and 0% and 5% in BPMZC (p<0.05 for all once-weekly regimens versus 4-month daily control; p>0.05 for all once-weekly regimens versus 6-month daily control).

CONCLUSIONS

BPZ-based once-weekly regimens have higher sterilising activity than the standard daily regimen and could greatly simplify treatment administration and possibly shorten the duration of tuberculosis treatment.

Dose-ranging comparison of rifampin and rifapentine in two pathologically distinct murine models of tuberculosis

In previous experiments, replacing the 10-mg/kg of body weight daily dose of rifampin with 7.5 to 10 mg/kg of rifapentine in combinations containing isoniazid and pyrazinamide reduced the duration of treatment needed to cure tuberculosis in BALB/c mice by approximately 50% due to rifapentine's more potent activity and greater drug exposures obtained. In the present study, we performed dose-ranging comparisons of the bactericidal and sterilizing activities of rifampin and rifapentine, alone and in combination with isoniazid and pyrazinamide with or without ethambutol, in BALB/c mice and in C3HeB/FeJ mice, which develop necrotic lung granulomas after infection with Mycobacterium tuberculosis. Each rifamycin demonstrated a significant increase in sterilizing activity with increasing dose. Rifapentine was roughly 4 times more potent in both mouse strains. These results reinforce the rationale for ongoing clinical trials to ascertain the highest well-tolerated doses of rifampin and rifapentine. This study also provides an important benchmark for the efficacy of the first-line regimen in C3HeB/FeJ mice, a strain in which the lung lesions observed after M. tuberculosis infection may better represent the pathology of human tuberculosis.

Short-course therapy with daily rifapentine in a murine model of latent tuberculosis infection

RATIONALE

Regimens recommended to treat latent tuberculosis infection (LTBI) are 3 to 9 months long. A 2-month rifampin+pyrazinamide regimen is no longer recommended. Shorter regimens are highly desirable. Because substituting rifapentine for rifampin in the standard regimen for active tuberculosis halves the treatment duration needed to prevent relapse in mice, we hypothesized daily rifapentine-based regimens could shorten LTBI treatment to 2 months or less.

OBJECTIVES

To improve an existing model of LTBI chemotherapy and evaluate the efficacy of daily rifapentine-based regimens.

METHODS

Mice were immunized with a more immunogenic recombinant Bacille Calmette-Guérin strain (rBCG30) and received very low-dose aerosol infection with Mycobacterium tuberculosis to establish a stable lung bacterial burden below 10(4) CFU without drug treatment. Mice received a control (isoniazid alone, rifampin alone, rifampin+isoniazid, rifampin+pyrazinamide) or test (rifapentine alone, rifapentine+isoniazid, rifapentine+pyrazinamide, rifapentine+isoniazid+pyrazinamide) regimen for 8 weeks. Rifamycin doses were 10 mg/kg/d, analogous to the same human doses. Outcomes were biweekly lung CFU counts and relapse after 4 to 8 weeks of treatment.

MEASUREMENTS AND MAIN RESULTS

M. tuberculosis CFU counts remained stable around 3.65 log(10) in immunized, untreated mice. Isoniazid or rifampin left all or most mice culture-positive at week 8. Rifampin+isoniazid cured 0 and 53% of mice and rifampin+pyrazinamide cured 47 and 100% of mice in 4 and 8 weeks, respectively. Rifapentine-based regimens were more active than rifampin+isoniazid and indistinguishable from rifampin+pyrazinamide.

CONCLUSIONS

In this improved murine model of LTBI chemotherapy with very low lung burden, existing regimens were well represented. Daily rifapentine-based regimens were at least as active as rifampin+pyrazinamide, suggesting they could effectively treat LTBI in 6 to 8 weeks.

A once-weekly R207910-containing regimen exceeds activity of the standard daily regimen in murine tuberculosis

RATIONALE

R207910 (TMC207 or J) is a member of the diarylquinolines, a new family of antituberculous drugs with high bactericidal activity when given daily in the murine model of tuberculosis. R207910 exhibits a long half-life and thus is a good candidate for once-weekly therapy of tuberculosis.

OBJECTIVES

To study the activity of once-weekly R207910 monotherapy and combinations of R207910 with other antituberculous agents (isoniazid, rifapentine, moxifloxacin, and pyrazinamide).

METHODS

The established infection model of murine tuberculosis was used. Colony counts were determined in the lungs.

MEASUREMENTS AND MAIN RESULTS

Eight weeks of monotherapy reduced the bacillary load by 3 to 4 log(10) for rifapentine and by 5 to 6 log(10) for R207910 (P < 0.05). The addition of rifapentine and isoniazid or moxifloxacin did not improve the bactericidal activity of R207910 monotherapy. In contrast, the triple combination of R207910 plus rifapentine plus pyrazinamide given once weekly for 2 months (i.e., a total of only eight administrations), was significantly (P < 0.05) more active than R207910 monotherapy or other R207910 combinations, and led to lung culture negativity in 9 of 10 mice, whereas all lungs were culture positive in the groups treated with other drug combinations. Moreover, R207910 plus rifapentine plus pyrazinamide given once weekly was more active than the current standard regimen of rifampin plus isoniazid plus pyrazinamide given five times per week.

CONCLUSIONS

The unprecedented activity of the triple combination of R207910 plus rifapentine plus pyrazinamide suggests that it may be feasible to develop a fully intermittent once-weekly regimen.

Tuberculous granulomas are hypoxic in guinea pigs, rabbits, and nonhuman primates

Understanding the physical characteristics of the local microenvironment in which Mycobacterium tuberculosis resides is an important goal that may allow the targeting of metabolic processes to shorten drug regimens. Pimonidazole hydrochloride (Hypoxyprobe) is an imaging agent that is bioreductively activated only under hypoxic conditions in mammalian tissue. We employed this probe to evaluate the oxygen tension in tuberculous granulomas in four animal models of disease: mouse, guinea pig, rabbit, and nonhuman primate. Following infusion of pimonidazole into animals with established infections, lung tissues from the guinea pig, rabbit, and nonhuman primate showed discrete areas of pimonidazole adduct formation surrounding necrotic and caseous regions of pulmonary granulomas by immunohistochemical staining. This labeling could be substantially reduced by housing the animal under an atmosphere of 95% O(2). Direct measurement of tissue oxygen partial pressure by surgical insertion of a fiber optic oxygen probe into granulomas in the lungs of living infected rabbits demonstrated that even small (3-mm) pulmonary lesions were severely hypoxic (1.6 +/- 0.7 mm Hg). Finally, metronidazole, which has potent bactericidal activity in vitro only under low-oxygen culture conditions, was highly effective at reducing total-lung bacterial burdens in infected rabbits. Thus, three independent lines of evidence support the hypothesis that hypoxic microenvironments are an important feature of some lesions in these animal models of tuberculosis.

Altered expression of isoniazid-regulated genes in drug-treated dormant Mycobacterium tuberculosis

OBJECTIVES

Despite having potent activity against actively replicating Mycobacterium tuberculosis, isoniazid has very limited activity against dormant bacilli. In order to investigate the lack of bactericidal activity of this drug under conditions leading to mycobacterial dormancy, we studied the transcriptional pattern of M. tuberculosis in different physiological states following exposure to isoniazid.

METHODS

Global gene expression analysis was used to study M. tuberculosis treated with isoniazid in dormancy models of nutrient depletion and progressive hypoxia in vitro, as well as in an in vivo hollow fibre model of dormancy. Mycobacterial expression of the drug's putative transcriptional signature was investigated by RT-PCR in each dormancy model, and during the early and chronic phases of infection in the mouse aerosol model. Transcriptional responses were correlated with the bactericidal activity of isoniazid in the respective models.

RESULTS

A small group of genes directly relevant to the mechanism of action of isoniazid was confirmed to constitute a transcriptional signature of the drug, as differential regulation of these genes was abrogated in an isoniazid-resistant, katG-deficient M. tuberculosis strain following isoniazid exposure. Isoniazid-induced expression of this transcriptional signature was abolished in dormant bacilli which had acquired phenotypic tolerance to isoniazid, regardless of the specific conditions responsible for the induction of the dormancy phenotype. Quantitative RT-PCR revealed that expression of isoniazid-regulated genes (IRGs) is dramatically altered under conditions of nutrient depletion and progressive hypoxia in vitro. Although these IRGs are highly induced following drug exposure early in infection in the mouse hollow fibre and aerosol models, correlating with potent bactericidal activity of the drug, their expression levels are markedly diminished during late-stage infection in these two models, coinciding with the greatly reduced bactericidal activity of isoniazid against these organisms.

CONCLUSIONS

The reduced susceptibility of bacilli to the bactericidal drug isoniazid, as well as lack of expression of IRGs upon exposure to the drug, may be defining features of M. tuberculosis dormancy.

Treatment of Latent Tuberculosis Infection: Challenges and Prospects

This article reviews the treatment of latent tuberculosis infection in HIV-seropositive and HIV-seronegative persons.

Effectiveness of once-weekly rifapentine and moxifloxacin regimens against Mycobacterium tuberculosis in mice

Mice infected with 1.6 x 10(7) CFU of Mycobacterium tuberculosis were treated 14 days later for 6 months with a regimen of once-weekly 10 mg of rifapentine and 75 mg of isoniazid per kg of body weight supplemented with either 150 mg of streptomycin per kg or 100 mg of moxifloxacin per kg during either both the 2-week daily initial and once-weekly continuation phases or only in the daily 2-week initial phase. On completion of treatment, all lung cultures were negative, except for three mice, each with a single colony: two whose rifapentine-isoniazid regimen was supplemented with streptomycin during the whole course of therapy and one whose rifapentine-isoniazid regimen had no initial daily phase, but was supplemented with streptomycin and moxifloxacin during the whole course of therapy. After 3 months of follow-up, positive lung cultures were obtained from 61 and 56% of mice supplemented with streptomycin during either the full course of therapy or only the daily 2-week initial phase, respectively, and 15 and 50% of mice supplemented with moxifloxacin during either the full course of therapy or only the daily 2-week initial phase, respectively. These results suggest that moxifloxacin has sterilizing activity against M. tuberculosis.

Evaluation of rifalazil in a combination treatment regimen as an alternative to isoniazid-rifampin therapy in a mouse tuberculosis model

The newer rifamycin, rifalazil (RLZ) (previously known as KRM-1648), has been shown in prior experiments to be a highly potent drug against Mycobacterium tuberculosis. In this report, we studied the efficacy of RLZ in combination with pyrazinamide (PZA) and ethambutol (EMB) in a long-term in vivo experiment and compared their activity with the isoniazid (INH)-rifampin (RIF) combination which is presently used in the clinic. Combinations of RLZ with PZA alone or with both PZA and EMB were both found to have sterilizing activities comparable to that of the INH-RIF combination but significantly better activity with respect to relapse of infection. These results suggest that RLZ, or other agents with similar activity, could be combined with available agents to act as a potential alternative drug regimen to the currently used INH-RIF combination.

Activity of rifapentine and its metabolite 25-O-desacetylrifapentine compared with rifampicin and rifabutin against Mycobacterium tuberculosis, Mycobacterium africanum, Mycobacterium bovis and M. bovis BCG

The in vitro activity of rifapentine and its metabolite, 25-O:-desacetylrifapentine, as compared with that of rifampicin and rifabutin, was determined against Mycobacterium tuberculosis, Mycobacterium africanum, Mycobacterium bovis and M. bovis BCG. MICs were determined radiometrically and by the 1% proportional method using Middlebrook 7H11 agar. The bactericidal effect of the drugs was determined in parallel at selected concentrations. For drugsusceptible isolates of M. tuberculosis, the Bactec MICs of rifapentine and 25-O:-desacetylrifapentine were 0.03-0.06 mg/L and 0. 125-0.25 mg/L, respectively. Similar MICs were obtained for M. africanum (0.03-0.125 and 0.125-0.50 mg/L, respectively), and M. bovis (0.063-0.25 and 0.125-1.0 mg/L, respectively), but MICs were considerably lower for M. bovis BCG (0.008-0.063 mg/L for rifapentine and 0.016-0.125 mg/L for its metabolite). In general, MICs determined using 7H11 agar medium were usually one or two dilutions higher than those obtained using Bactec broth. When compared with rifampicin and rifabutin, the inhibitory activity of rifapentine for drug-susceptible isolates was roughly equal to that of rifabutin, and the inhibitory activity of 25-O:-desacetylrifapentine was comparable to that of rifampicin; however, rifapentine was somewhat more bactericidal than rifabutin at equal concentrations. Clinical isolates of M. tuberculosis with a high degree of resistance to rifampicin (MIC >/= 32 mg/L) were also highly resistant to rifabutin, rifapentine and 25-O:-desacetylrifapentine, although the MICs of rifabutin in this case were somewhat lower than the MICs of rifapentine.

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.

Durable cure for tuberculosis: rifalazil in combination with isoniazid in a murine model of Mycobacterium tuberculosis infection

Rifalazil (formerly known as KRM-1648) in combination with isoniazid has been found to be more active than rifampin/isoniazid. Administration of rifalazil/isoniazid for 12 weeks resulted in continued apparent sterilization of organs 6 months after cessation of therapy. In this study we evaluated the durability of rifalazil/isoniazid treatment. Female CD-1 mice were infected with Mycobacterium tuberculosis ATCC 35801 (strain Erdman). Rifalazil and isoniazid were given in combination for 6 and 12 weeks; no mycobacteria could be cultured from spleens and lungs at both the 6-week and 12-week time points. After completing treatment, groups of mice treated with rifalazil/isoniazid for 6 or 12 weeks were observed without any additional treatment. These observation groups were compared to groups of rifalazil/isoniazid-treated mice (6 and 12 weeks) given dexamethasone for 7 and 8 weeks, respectively. Modest regrowth was noted in the spleens and lungs of the group treated with rifalazil/isoniazid for 6 weeks. Regrowth in the 6-weeks group was enhanced slightly by treatment with dexamethasone. In contrast, no regrowth was noted in the 12-weeks rifalazil/isoniazid group, and treatment with dexamethasone did not result in any regrowth.

Antituberculosis activity of once-weekly rifapentine-containing regimens in mice. Long-term effectiveness with 6- and 8-month treatment regimens

The effectiveness of various once-weekly 10 mg/kg rifapentine (P)- containing regimens for treatment of tuberculosis was assessed in mice infected intravenously with 4.3 x 10(6) colony-forming units (cfu) of Mycobacterium tuberculosis H37Rv, and treated 14 d later with various combinations of rifampin (R), P, isoniazid (H), pyrazinamide (Z), ethambutol (E), or streptomycin (S). Control mice treated daily with either 2-mo HRZ + 4-mo HR or 2-mo HRZ + 6-mo HE were rendered spleen and lung culture-negative at 6 mo and 8 mo, respectively. Treatment failure with emergence of R-resistant bacilli occurred in all mice given once-weekly monotherapy with P for 6 mo. Once-weekly PH treatment was successful at 6 mo when it was preceded by a 2-mo daily phase with HRZ. When the initial daily phase was reduced to 2 wk, once-weekly PH-containing treatment was successful, at 6 mo, only if it was supplemented with S during the initial daily and the once-weekly phases, and at 8 mo if it was supplemented with daily H during the once-weekly phase. Without these supplements, once-weekly treatment failed in some mice with selection of R-resistant or H-resistant mutants.

Rifapentine: its role in the treatment of tuberculosis

OBJECTIVE

To review the pharmacokinetics, efficacy, adverse effects, and cost of the newest antitubercular drug, rifapentine.

DATA SOURCES

A MEDLINE search using key terms such as rifapentine, rifampin, isoniazid, Mycobacterium tuberculosis, and pyrazinamide was conducted for the time period 1966-November 1998.

STUDY SELECTION

Animal data were used for basic information and human studies were selected for inclusion if they were randomized, controlled studies assessing efficacy, or if they were single- or multiple-dose studies assessing the pharmacokinetics of rifapentine. Background articles on the pathophysiology of tuberculosis and cost of care and noncontrolled studies assessing drug interactions were also included.

DATA SYNTHESIS

Compared with an oral solution, the relative bioavailability of rifapentine is 70% following oral admninistration of tablets. Food increased bioavailability by 55%. Rifapentine accumulated significantly in human macrophages and its elimination half-life was longer than that of rifampin. Comparative studies of rifapentine and rifampin in humans during intensive- and continuation-phase treatment of tuberculosis suggest that at currently accepted doses, rifapentine was slightly less effective than rifampin. The most significant drug interaction with rifapentine involves indinavir: the maximum concentration and AUC of indinavir are reduced by 55% and 70%, respectively, when rifapentine is coadministered with indinavir. Adverse events of rifapentine may occur less frequently at the currently recommended 600-mg dose as compared with rifampin; however, the difference was not statistically significant. If only drug costs were evaluated during the six-month treatment of tuberculosis, rifapentine is more expensive than rifampin.

CONCLUSIONS

Rifapentine can be administered twice weekly during the intensive phase of tuberculosis treatment and then once weekly during the continuation phase of treatment. This may improve patient adherence over some other treatments and possibly reduce costs of treatment by preventing development of resistant tubercular strains due to nonadherence. Rifapentine is well tolerated, with most patients experiencing adverse effects at a similar rate as rifampin. Rifapentine induces cytochrome P450 somewhat less than rifampin, although few drug interaction studies have been done with rifapentine. Its efficacy at the currently approved dosage of 600 mg may be slightly lower than that of rifampin. Studies are needed to determine if equal or greater efficacy can be achieved with higher doses of rifapentine. Rifampin is less expensive than rifapentine. Further pharmacoeconomic studies are needed to evaluate costs of relapse and failure in patients receiving these agents.

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

Besides direct bactericidal activity, long-term effectiveness is one of the most important features to consider when developing new drugs for chemotherapy. In this study, we evaluated the ability of rifapentine (RFP), in monotherapy and combination therapy, to completely eradicate a Mycobacterium tuberculosis infection and to prevent relapse posttreatment in a Swiss mouse model. The combination of RFP, isoniazid (INH), and pyrazinamide (PZA) administered daily resulted in an apparent clearance of M. tuberculosis organisms in the lungs and spleens of infected mice after 10 weeks of treatment. However, 3 months after the cessation of therapy, bacterial regrowth occurred in mice treated for a 12-week period, indicating a relapse of infection. In intermittent treatment regimens of RFP in combination with INH and PZA, sterilization was achieved when mice were treated two to five times per week for 9 weeks. Bacterial growth was still observed in the once-weekly treatment group. Our results show that mouse models can predict important parameters for new drugs. We stress the necessity for long-term posttreatment observation in animal models for the routine evaluation of new drugs for antituberculosis chemotherapy.

Analysis of rifapentine for preventive therapy in the Cornell mouse model of latent tuberculosis

Rifapentine is a long-acting rifamycin which may be useful for intermittent drug therapy against tuberculosis. In this study we measured the efficacies of rifapentine-containing intermittent drug regimens for preventive therapy using the Cornell mouse model of latent tuberculosis. We infected groups of mice intravenously with Mycobacterium tuberculosis and then treated them with isoniazid and pyrazinamide for 12 weeks according to the Cornell latency development protocol. After a 4-week interval of no treatment, experimental preventive therapy was administered by esophageal gavage for 12 or 18 weeks. After equilibration and dexamethasone amplification treatment, mouse organs were analyzed by quantitative colony counts to measure the effectiveness of therapy. Our results showed that once-weekly isoniazid plus rifapentine combination therapy for 18 weeks was an effective preventive regimen with sterilizing potency and bacillary load reduction comparable to those of daily isoniazid therapy for 18 weeks. Monotherapy with rifapentine weekly or fortnightly or with rifampin twice weekly for up to 18 weeks did not offer advantages in reducing bacillary load or in sterilizing organs compared to the effects of a placebo. These results with the Cornell mouse model indicate that once-weekly, short-course preventive therapy with isoniazid plus rifapentine is effective and may warrant investigation in humans with latent tuberculosis infection.

Acquired rifamycin monoresistance in patients with HIV-related tuberculosis treated with once-weekly rifapentine and isoniazid. Tuberculosis Trials Consortium

BACKGROUND

Rifapentine is a cyclopentyl-substituted rifamycin whose serum half-life is five times that of rifampin. The US Public Health Service Study 22 compared a once-weekly regimen of isoniazid and rifapentine with twice weekly isoniazid and rifampin in the continuation phase (the last 4 months) of treatment for pulmonary tuberculosis in HIV-seropositive and HIV-seronegative patients. This report concerns only the HIV-seropositive part of the trial, which has ended. The HIV-seronegative part will stop follow-up in 2001.

METHODS

Adults with culture-positive, drug-susceptible pulmonary tuberculosis who completed 2 months of four-drug (isoniazid, rifampin, pyrazinamide, ethambutol) treatment (induction phase) were randomly assigned 900 mg isoniazid and 600 mg rifapentine once weekly, or 900 mg isoniazid and 600 mg rifampin twice weekly. All therapy was directly observed. Statistical analysis used univariate, Kaplan-Meier, and logistic and proportional hazards regression methods.

FINDINGS

71 HIV-seropositive patients were enrolled: 61 completed therapy and were assessed for relapse. Five of 30 patients in the once-weekly isoniazid/rifapentine group relapsed, compared with three of 31 patients in the twice-weekly isoniazid/rifampin group (log rank chi2=0.69, p=0.41). However, four of five relapses in the once-weekly isoniazid/rifapentine group had monoresistance to rifamycin, compared with none of three in the rifampin group (p=0.05). Patients who relapsed with rifamycin monoresistance were younger (median age 29 vs 41 years), had lower baseline CD4 cell counts (median 16 vs 144 microL), and were more likely to have extrapulmonary involvement (75% vs 18%, p=0.03) and concomitant therapy with antifungal agents (75% vs 9%, p=0.006). No rifamycin monoresistant relapse has occurred among 1004 HIV-seronegative patients enrolled to date.

INTERPRETATION

Relapse with rifamycin monoresistant tuberculosis occurred among HIV-seropositive tuberculosis patients treated with a once-weekly isoniazid/rifapentine continuation-phase regimen. Until more effective regimens have been identified and assessed in clinical trials, HIV-seropositive people with tuberculosis should not be treated with a once-weekly isoniazid/rifapentine regimen.

Pulmonary tuberculosis

Pulmonary tuberculosis is a major cause of morbidity and mortality worldwide, resulting in the greatest number of deaths due to any one single infectious agent. This trend is due, at least in part, to increasing numbers of individuals co-infected with HIV and Mycobacterium tuberculosis (MTB). Concerted efforts between the World Health Organization and other agencies, therefore, are underway to improve tuberculosis control worldwide. These include basic research in tuberculosis diagnostics and vaccine development, institution of preventive therapy in individuals dually infected with HIV and MTB, and directly observed short-course antituberculous therapy in developing countries with a high prevalence of MTB infection. Further, newer, longer-acting antituberculous therapeutic agents such as rifapentine, which allow twice-weekly dosing in the continuation phase of anti-MTB therapy, have recently been released and are undergoing clinical trials. This review provides a synopsis of recent developments in these areas and serves as a reference source for interested readers.

Recent Developments in Epidemiology, Treatment, and Diagnosis of Tuberculosis

The resurgence in cases of active tuberculosis in North America in the past decade has prompted increases in funding for tuberculosis treatment, research, and education. As a result, the number of new cases of tuberculosis has declined and cases occur in smaller pockets of well-characterized populations, such as communities of foreign-born persons and socioeconomically disadvantaged groups. New strategies for the treatment of both active and latent tuberculosis may soon include the newly licensed, long-acting rifamycin, rifapentine, but further studies are needed to determine optimal dosing regimens for this agent. Experts in tuberculosis and HIV infection have made headway in defining the optimal therapy for each current therapeutic option, and recently published guidelines are a useful document for clinicians. Rifabutin-based regimens are one approach toward achieving the optimal treatment of both diseases simultaneously. Finally, newly licensed molecular diagnostic tests for direct use on clinical specimens are intriguing, but their clinical utility remains to be defined.