Comparison of activities of rifapentine and rifampin against Mycobacterium tuberculosis residing in human macrophages

Efficacy of rifapentine and other rifamycins against Coxiella burnetii in vitro

Since 1999, doxycycline and hydroxychloroquine have been the recommended treatment for chronic Q fever, a life-threatening disease caused by the bacterial pathogen, Coxiella burnetii. Despite the duration of its use, the treatment is not ideal due to the lengthy treatment time, high mortality rate, resistant strains, and the potential for contraindicated usage. A literature search was conducted to identify studies that screened large panels of drugs against C. burnetii to identify novel targets with potential efficacy against C. burnetii. Twelve candidate antimicrobials approved for use in humans by the US Food and Drug Administration were selected and minimum inhibitory concentrations (MICs) were determined against the low virulence strain Nine Mile phase II. Rifabutin and rifaximin were the best performing antibiotics tested with MICs of ≤0.01 µg mL-1. Further screening of these top candidates was conducted alongside two drugs from the same class, rifampin, well-characterized, and rifapentine, not previously reported against C. burnetii. These were screened against virulent strains of C. burnetii representing three clinically relevant genotypes. Rifapentine was the most effective in the human monocytic leukemia cell line, THP-1, with a MIC ≤0.01 µg mL-1. In the human kidney epithelial cell line, A-498, efficacy of rifapentine, rifampin, and rifabutin varied across C. burnetii strains with MICs between ≤0.001 and 0.01 µg mL-1. Rifampin, rifabutin, and rifapentine were all bactericidal against C. burnetii; however, rifabutin and rifapentine demonstrated impressive bactericidal activity as low as 0.1 µg mL-1 and should be further explored as alternative Q fever treatments given their efficacy in vitro.

IMPORTANCE

This work will help inform investigators and physicians about potential alternative antimicrobial therapies targeting the causative agent of Q fever, Coxiella burnetii. Chronic Q fever is difficult to treat, and alternative antimicrobials are needed. This manuscript explores the efficacy of rifamycin antibiotics against virulent strains of C. burnetii representing three clinically relevant genotypes in vitro. Importantly, this study determines the susceptibility of C. burnetii to rifapentine, which has not been previously reported. Evaluation of the bactericidal activity of the rifamycins reveals that rifabutin and rifapentine are bactericidal at low concentrations, which is unusual for antibiotics against C. burnetii.

Extrapolation of lung pharmacokinetics of antitubercular drugs from preclinical species to humans using PBPK modelling

OBJECTIVES

To develop physiologically based pharmacokinetic (PBPK) models for widely used anti-TB drugs, namely rifampicin, pyrazinamide, isoniazid, ethambutol and moxifloxacin lung pharmacokinetics (PK)-regarding both healthy and TB-infected tissue (cellular lesion and caseum)-in preclinical species and to extrapolate to humans.

METHODS

Empirical models were used for the plasma PK of each species, which were connected to multicompartment permeability-limited lung models within a middle-out PBPK approach with an appropriate physiological parameterization that was scalable across species. Lung's extracellular water (EW) was assumed to be the linking component between healthy and infected tissue, while passive diffusion was assumed for the drug transferring between cellular lesion and caseum.

RESULTS

In rabbits, optimized unbound fractions in intracellular water of rifampicin, moxifloxacin and ethambutol were 0.015, 0.056 and 0.08, respectively, while the optimized unbound fractions in EW of pyrazinamide and isoniazid in mice were 0.25 and 0.17, respectively. In humans, all mean extrapolated daily AUC and Cmax values of various lung regions were within 2-fold of the observed ones. Unbound concentrations in the caseum were lower than unbound plasma concentrations for both rifampicin and moxifloxacin. For rifampicin, unbound concentrations in cellular rim are slightly lower, while for moxifloxacin they are significantly higher than unbound plasma concentrations.

CONCLUSIONS

The developed PBPK approach was able to extrapolate lung PK from preclinical species to humans and to predict unbound concentrations in the various TB-infected regions, unlike empirical lung models. We found that plasma free drug PK is not always a good surrogate for TB-infected tissue unbound PK.

An Overview of Various Rifampicin Analogs against Mycobacterium tuberculosis and their Drug Interactions

The success of the TB control program is hampered by the major issue of drug-resistant tuberculosis (DR-TB). The situation has undoubtedly been made more difficult by the widespread and multidrug-resistant (XDR) strains of TB. The modification of existing anti-TB medications to produce derivatives that can function on resistant TB bacilli is one of the potential techniques to overcome drug resistance affordably and straightforwardly. In comparison to novel pharmaceuticals for drug research and progress, these may have a better half-life and greater bioavailability, be more efficient, and serve as inexpensive alternatives. Mycobacterium tuberculosis, which is drugsusceptible or drug-resistant, is effectively treated by several already prescribed medications and their derivatives. Due to this, the current review attempts to give a brief overview of the rifampicin derivatives that can overcome the parent drug's resistance and could, hence, act as useful substitutes. It has been found that one-third of the global population is affected by M. tuberculosis. The most common cause of infection-related death can range from latent TB to TB illness. Antibiotics in the rifamycin class, including rifampicin or rifampin (RIF), rifapentine (RPT), and others, have a special sterilizing effect on M. tuberculosis. We examine research focused on evaluating the safety, effectiveness, pharmacokinetics, pharmacodynamics, risk of medication interactions, and other characteristics of RIF analogs. Drug interactions are especially difficult with RIF because it must be taken every day for four months to treat latent TB infection. RIF continues to be the gold standard of treatment for drug-sensitive TB illness. RIF's safety profile is well known, and the two medicines' adverse reactions have varying degrees of frequency. The authorized once-weekly RPT regimen is insufficient, but greater dosages of either medication may reduce the amount of time needed to treat TB effectively.

Macrophage internalization creates a multidrug-tolerant fungal persister reservoir and facilitates the emergence of drug resistance

Candida glabrata is a major fungal pathogen notable for causing recalcitrant infections, rapid emergence of drug-resistant strains, and its ability to survive and proliferate within macrophages. Resembling bacterial persisters, a subset of genetically drug-susceptible C. glabrata cells can survive lethal exposure to the fungicidal echinocandin drugs. Herein, we show that macrophage internalization induces cidal drug tolerance in C. glabrata, expanding the persister reservoir from which echinocandin-resistant mutants emerge. We show that this drug tolerance is associated with non-proliferation and is triggered by macrophage-induced oxidative stress, and that deletion of genes involved in reactive oxygen species detoxification significantly increases the emergence of echinocandin-resistant mutants. Finally, we show that the fungicidal drug amphotericin B can kill intracellular C. glabrata echinocandin persisters, reducing emergence of resistance. Our study supports the hypothesis that intra-macrophage C. glabrata is a reservoir of recalcitrant/drug-resistant infections, and that drug alternating strategies can be developed to eliminate this reservoir.

New and Repurposed Drugs for the Treatment of Active Tuberculosis: An Update for Clinicians

Although tuberculosis (TB) is preventable and curable, the lengthy treatment (generally 6 months), poor patient adherence, high inter-individual variability in pharmacokinetics (PK), emergence of drug resistance, presence of comorbidities, and adverse drug reactions complicate TB therapy and drive the need for new drugs and/or regimens. Hence, new compounds are being developed, available drugs are repurposed, and the dosing of existing drugs is optimized, resulting in the largest drug development portfolio in TB history. This review highlights a selection of clinically available drug candidates that could be part of future TB regimens, including bedaquiline, delamanid, pretomanid, linezolid, clofazimine, optimized (high dose) rifampicin, rifapentine, and para-aminosalicylic acid. The review covers drug development history, preclinical data, PK, and current clinical development.

Deletion of rifampicin-inactivating mono-ADP-ribosyl transferase gene of Mycobacterium smegmatis globally altered gene expression profile that favoured increase in ROS levels and thereby antibiotic resister generation

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Physiological role of mono-ADP-ribosyl transferase (Arr) of Mycobacterium smegmatis revealed.

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Arr is required to maintain ROS levels in actively growing M. smegmatis.

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Arr influences gene expression at global level in several pathways.

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Expression of electron transfer, antioxidation, and DNA repair genes are influenced by Arr.

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Arr is required to maintain an optimal oxidative and metabolic status.

The physiological role of mono-ADP-ribosyl transferase (Arr) of Mycobacterium smegmatis, which inactivates rifampicin, remains unclear. An earlier study reported increased expression of arr during oxidative stress and DNA damage. This suggested a role for Arr in the oxidative status of the cell and its associated effect on DNA damage. Since reactive oxygen species (ROS) influence oxidative status, we investigated whether Arr affected ROS levels in M. smegmatis. Significantly elevated levels of superoxide and hydroxyl radical were found in the mid-log phase (MLP) cultures of the arr knockout strain (arr-KO) as compared those in the wild-type strain (WT). Complementation of arr-KO with expression from genomically integrated arr under its native promoter restored the levels of ROS equivalent to that in WT. Due to the inherently high ROS levels in the actively growing arr-KO, rifampicin resisters with rpoB mutations could be selected at 0 hr of exposure itself against rifampicin, unlike in the WT where the resisters emerged at 12^th hr of rifampicin exposure. Microarray analysis of the actively growing cultures of arr-KO revealed significantly high levels of expression of genes from succinate dehydrogenase I and NADH dehydrogenase I operons, which would have contributed to the increased superoxide levels. In parallel, expression of specific DNA repair genes was significantly decreased, favouring retention of the mutations inflicted by the ROS. Expression of several metabolic pathway genes also was significantly altered. These observations revealed that Arr was required for maintaining a gene expression profile that would provide optimum levels of ROS and DNA repair system in the actively growing M. smegmatis.

Mycobacterium smegmatis strains genetically resistant to moxifloxacin emerge de novo from the moxifloxacin-surviving population containing high levels of superoxide, H2O2, hydroxyl radical, and Fe (II)

Background

The antibiotic-exposed bacteria often contain the reactive oxygen species (ROS), hydroxyl radical, which inflicts genome-wide mutations, causing the de novo formation of antibiotic-resistant strains. Hydroxyl radical is generated by Fenton reaction of Fe (II) with the ROS, H₂O₂, which, in turn, is formed by the dismutation of the ROS, superoxide. Therefore, for the emergence of bacterial strains genetically resistant to antibiotics, increased levels of superoxide, H₂O₂, hydroxyl radical, and Fe (II) should be present in the antibiotic-exposed bacteria. Here, we verified this premise by finding out whether the in vitro cultures of M. smegmatis, exposed to MBC of moxifloxacin for a prolonged duration, contain significantly high levels of superoxide, H₂O₂, hydroxyl radical, and Fe (II).

Methods

Biological triplicate cultures of M. smegmatis, were exposed to MBC of moxifloxacin for 84 h. The colony-forming units (CFUs) of the cultures were determined on moxifloxacin-free and moxifloxacin-containing plates for the entire 84 h at a regular interval of 6 h. The cultures were analyzed at specific time points of killing phase (KP), antibiotic-surviving phase (ASP), and regrowth phase (RGP) for the presence of superoxide, H₂O₂, hydroxyl radical, and Fe (II) using the ROS- and Fe (II)-detecting fluorescence probes. The experimental cultures were grown in the presence of ROS and Fe (II) quenchers also and determined the levels of fluorescence corresponding to the ROS- and Fe (II)-specific probes. This was performed to establish the specificity of detection of ROS and Fe (II). Biological triplicate cultures, unexposed to moxifloxacin but cultured for 84 h, were used as the control for the measurement of ROS and Fe (II) levels. The CFUs of the cultures were determined on moxifloxacin-free and moxifloxacin-containing plates for the entire 84 h at regular intervals of 6 h. Flow cytometry analyses were performed for the detection and quantitation of the levels of fluorescence of the ROS-and Fe (II)-specific probes. The experimental cultures were grown in the presence of thiourea and bipyridyl as the ROS and Fe (II) quenchers, respectively, for the determination of the levels of fluorescence corresponding to the ROS- and Fe (II)-specific probes. Paired t-test was used to calculate statistical significance (n = 3).

Results

The moxifloxacin-exposed cultures, but not the cultures unexposed to moxifloxacin, showed a triphasic response with a KP, ASP, and RGP. The cells in the late KP and ASP contained significantly elevated levels of superoxide, H₂O₂, hydroxyl radical, and Fe (II). Thus, high levels of the ROS and Fe (II) were found in the small population (in the ASP) of M. smegmatis cells that survived the moxifloxacin-mediated killing. From this moxifloxacin-surviving population (in the ASP), moxifloxacin-resistant genetic resisters emerged de novo at high frequency, regrew, divided, and populated the cultures. The levels of these ROS, Fe (II), and the high moxifloxacin resister generation frequency were quenched in the cultures grown in the presence of the respective ROS and Fe (II) quenchers. The cultures unexposed to moxifloxacin did not show any of these responses, indicating that the whole response was specific to antibiotic exposure.

Conclusions

Significantly high levels of superoxide, H₂O₂, hydroxyl radical, and Fe (II) were generated in the M. smegmatis cultures exposed to moxifloxacin for a prolonged duration. It promoted the de novo emergence of genetic resisters to moxifloxacin at high frequency.

Unique Mode of Cell Division by the Mycobacterial Genetic Resister Clones Emerging De Novo from the Antibiotic-Surviving Population

The bacterial pathogens that are tolerant to antibiotics and survive in the continued presence of antibiotics have the chance to acquire genetically resistant mutations against the antibiotics and emerge de novo as antibiotic resisters. Once the antibiotic resister clone has emerged, often with compromise on growth characteristics, for the protection of the species, it is important to establish an antibiotic-resistant population quickly in the continued presence of the antibiotic. In this regard, the present study has unraveled multinucleation and multiseptation followed by multiple constrictions as the cellular processes used by the bacteria for quick multiplication to establish antibiotic-resistant populations. The study also points out the same phenomenon occurring in other bacterial systems investigated in our laboratory and others’ laboratories. Identification of these specific cellular events involved in quick multiplication offers additional cellular processes that can be targeted in combination with the existing antibiotics’ targets to preempt the emergence of antibiotic-resistant bacterial strains.

The emergence of antibiotic genetic resisters of pathogenic bacteria poses a major public health challenge. The mechanism by which bacterial antibiotic genetic resister clones formed de novo multiply and establish a resister population remained unknown. Here, we delineated the unique mode of cell division of the antibiotic genetic resisters of Mycobacterium smegmatis and Mycobacterium tuberculosis formed de novo from the population surviving in the presence of bactericidal concentrations of rifampicin or moxifloxacin. The cells in the rifampicin/moxifloxacin-surviving population generated elevated levels of hydroxyl radical-inflicting mutations. The genetic mutants selected against rifampicin/moxifloxacin became multinucleated and multiseptated and developed multiple constrictions. These cells stochastically divided multiple times, producing sister-daughter cells phenomenally higher in number than what could be expected from their generation time. This caused an abrupt, unexpectedly high increase in the rifampicin/moxifloxacin resister colonies. This unique cell division behavior was not shown by the rifampicin resisters formed naturally in the actively growing cultures. We could detect such abrupt increases in the antibiotic resisters in others’ and our earlier data on the antibiotic-exposed laboratory/clinical M. tuberculosis strains, M. smegmatis and other bacteria in in vitro cultures, infected macrophages/animals, and tuberculosis patients. However, it went unnoticed/unreported in all those studies. This phenomenon occurring in diverse bacteria surviving against different antibiotics revealed the broad significance of the present study. We speculate that the antibiotic-resistant bacillary clones, which emerge in patients with diverse bacterial infections, might be using the same mechanism to establish an antibiotic resister population quickly in the continued presence of antibiotics.

IMPORTANCE The bacterial pathogens that are tolerant to antibiotics and survive in the continued presence of antibiotics have the chance to acquire genetically resistant mutations against the antibiotics and emerge de novo as antibiotic resisters. Once the antibiotic resister clone has emerged, often with compromise on growth characteristics, for the protection of the species, it is important to establish an antibiotic-resistant population quickly in the continued presence of the antibiotic. In this regard, the present study has unraveled multinucleation and multiseptation followed by multiple constrictions as the cellular processes used by the bacteria for quick multiplication to establish antibiotic-resistant populations. The study also points out the same phenomenon occurring in other bacterial systems investigated in our laboratory and others’ laboratories. Identification of these specific cellular events involved in quick multiplication offers additional cellular processes that can be targeted in combination with the existing antibiotics’ targets to preempt the emergence of antibiotic-resistant bacterial strains.

Hepatocytic transcriptional signatures predict comparative drug interaction potential of rifamycin antibiotics

Current strategies to treat tuberculosis (TB) and co-morbidities involve multidrug combination therapies. Rifamycin antibiotics are a key component of TB therapy and a common source of drug–drug interactions (DDIs) due to induction of drug metabolizing enzymes (DMEs). Management of rifamycin DDIs are complex, particularly in patients with co-morbidities, and differences in DDI potential between rifamycin antibiotics are not well established. DME profiles induced in response to tuberculosis antibiotics (rifampin, rifabutin and rifapentine) were compared in primary human hepatocytes. We identified rifamycin induced DMEs, cytochrome P450 (CYP) 2C8/3A4/3A5, SULT2A, and UGT1A4/1A5 and predicted lower DDIs of rifapentine with 58 clinical drugs used to treat co-morbidities in TB patients. Transcriptional networks and upstream regulator analyses showed FOXA3, HNF4α, NR1I2, NR1I3, NR3C1 and RXRα as key transcriptional regulators of rifamycin induced DMEs. Our study findings are an important resource to design effective medication regimens to treat common co-conditions in TB patients.

Inhalable dry powders of rifampicin highlighting potential and drawbacks in formulation development for experimental tuberculosis aerosol therapy

Introduction: Recently, tuberculosis was reported as the leading cause of death from a single infectious agent. Standard therapy includes administration of four first-line antibiotics, i.e. rifampicin, isoniazid, ethambutol, and pyrazinamide over a period of at least 26 weeks, which in case of rifampicin oftentimes is accompanied by unwanted side effects and variable bioavailability that compromise a positive therapeutic outcome. As the main site of infection is the lungs, it is desirable to develop a therapeutic formulation to be administered via the pulmonary route.Areas covered: This work presents a literature review on studies investigating inhalable dry powder formulations including rifampicin in the context of an experimental tuberculosis therapy, with a special focus on aerosol performance.Expert opinion: It was found that formulation approaches involving different strategies and functional excipients are under investigation but as of now, no formulation has managed to leap into commercial clinical testing. Reasons for this might not primarily be associated with a lack of suitable candidates, but amongst others a lack of suitable in vitro models to assess the efficacy, therapeutic benefit, and cost-effectiveness of the candidate formulations.

Minimum Bactericidal Concentration Techniques in Mycobacterium tuberculosis: A Systematic Review

Minimum bactericidal concentration (MBC) assay is an accepted parameter for evaluating new antimicrobial agents, and it is frequently used as a research tool to provide a prediction of bacterial eradication. To the best of our knowledge, there is no standardization among researchers regarding the technique used to detect a drug's MBC in Mycobacterium tuberculosis. Thus, the aim of this systematic review is to discuss the available literature in determining a drug's MBC in M. tuberculosis, to find the most commonly used technique and standardize the process. A broad and rigorous literature search of three electronic databases (PubMed, Web of Knowledge, and LILACS) was performed according to the PRISMA statement. We considered studies that were published from January 1, 1990 to February 19, 2019. Google Scholar was also searched to increase the number of publications. We searched for articles using the MeSH terms "microbiological techniques," "Mycobacterium," "antibacterial agents." In addition, free terms were used in the search. The search yielded 6,674 publications. After filter application, 5,348 publications remained. Of these, we evaluated the full text of 187 publications. By applying the inclusion criteria, 69 studies were included in the present systematic review. In the literature analyzed, a great variety in the techniques used to determine a drug's MBC in M. tuberculosis was observed. The most common variability is related to the culture media used, culture incubation time, and the percentage of bacterial death for the drug to be considered as bactericidal. The most commonly used technique for drug's MBC determination was carried out using the drug's minimum inhibitory concentration (MIC) assay. Aliquots from prior MIC values were subcultured in Middlebrook agar and incubated for 4 weeks at 35°C for determining the colony forming unit (CFU) with relevance to detect 99.9% bacilli killed or reduction in 3 log₁₀ viable bacilli.

Chaves L, C. Vieira A, G. Santos S, Pinheiro M, Reis S. Optimization of Rifapentine-Loaded Lipid Nanoparticles Using a Quality-by-Design Strategy

This work aims to optimize and assess the potential use of lipid nanoparticles, namely nanostructured lipid carriers (NLCs), as drug delivery systems of rifapentine (RPT) for the treatment of tuberculosis (TB). A Box–Behnken design was used to increase drug encapsulation efficiency (EE) and loading capacity (LC) of RPT-loaded NLCs. The optimized nanoparticles were fully characterized, and their effect on cell viability was assessed. The quality-by-design approach allowed the optimization of RPT-loaded NLCs with improved EE and LC using the minimum of experiments. Analyses of variance were indicative of the validity of this model to optimize this nanodelivery system. The optimized NLCs had a mean diameter of 242 ± 9 nm, polydispersity index <0.2, and a highly negative zeta potential. EE values were higher than 80%, and differential scanning calorimetry analysis enabled the confirmation of the efficient encapsulation of RPT. Transmission electron microscopy analysis showed spherical nanoparticles, uniform in shape and diameter, with no visible aggregation. Stability studies indicated that NLCs were stable over time. No toxicity was observed in primary human macrophage viability for nanoparticles up to 1000 μg mL⁻¹. Overall, the optimized NLCs are efficient carriers of RPT and should be considered for further testing as promising drug delivery systems to be used in TB treatment.

Treatment-Shortening Effect of a Novel Regimen Combining Clofazimine and High-Dose Rifapentine in Pathologically Distinct Mouse Models of Tuberculosis

Clofazimine and high-dose rifapentine have each separately been associated with treatment-shortening activity when incorporated into tuberculosis (TB) treatment regimens. We hypothesized that both modifications, i.e., the addition of clofazimine and the replacement of rifampin with high-dose rifapentine, in the first-line regimen for drug-susceptible TB would significantly shorten the duration of treatment necessary for cure. We tested this hypothesis in a well-established BALB/c mouse model of TB chemotherapy and also in a C3HeB/FeJ mouse model in which mice can develop caseous necrotic lesions, an environment where rifapentine and clofazimine may individually be less effective. In both mouse models, replacing rifampin with high-dose rifapentine and adding clofazimine in the first-line regimen resulted in greater bactericidal and sterilizing activity than either modification alone, suggesting that a rifapentine- and clofazimine-containing regimen may have the potential to significantly shorten the treatment duration for drug-susceptible TB. These data provide preclinical evidence supporting the evaluation of regimens combining high-dose rifapentine and clofazimine in clinical trials.

Development of dual delivery antituberculotic system containing rifapentine microspheres and adipose stem cells seeded in hydroxyapatite/tricalcium phosphate

Background

Low drug concentration in the tuberculosis (TB) lesion and bone defects or nonunion after debridement are two major problems that occur in the course of treating osteo-articular TB. Thus, the combination of drug-delivery system and bone tissue repair appears to be the most promising option for osteoarticular TB treatment.

Materials and methods

Herein, we report a novel anti-TB dual delivery system based on rifapentine polylactic acid microspheres (RPMs) to treat infections, with the addition of adipose-derived mesenchymal stem cells (ASCs) seeded in hydroxyapatite/tricalcium phosphate (HA/TCP) to promote bone formation. Cell proliferation, osteogenesis, and apoptosis were performed to investigate the effects of rifapentine on ASCs. The RPMs were synthesized by emulsion-solvent evaporation method, and then the monolayer composite (ASC + RPM) and three-dimensional (3D) composite scaffold (ASC + RPM + HA/TCP) were constructed, respectively. The alkaline phosphatase (ALP) activity and real-time PCR were used for determining the osteogenic differentiation. The concentrations of rifapentine resulting from the composites were detected.

Results

The results showed that rifapentine has no influence on ASCs proliferation and osteogenesis when the drug concentration was below 20 µg/mL, which was significantly higher than minimal inhibitory concentration. The drug loading and encapsulation efficiency of RPMs were 40.56%±2.63% and 70.24%±2.18%, respectively. The proliferation of the cells in monolayer was higher than that in 3D composite, and the addition of RPMs slightly increased the proliferation. The ALP activity and gene expression of osteocalcin and osteopontin were higher in the 3D composite than those in the monolayer. Good biocompatibility was observed by microscopic image and H&E stain. The release tests revealed that the 3D composite exhibited sustained release profiles of rifapentine for 76 days. The dual delivery systems in 3D composite could moderate the burst release and extend the length of release time when compared to single delivery in monolayers.

Conclusion

In conclusion, such dual delivery antituberculotic scaffold represents a potential new strategy for TB infections and bone defects.

An explant technique for high-resolution imaging and manipulation of mycobacterial granulomas

A central and critical structure in tuberculosis, the mycobacterial granuloma consists of highly organized immune cells, including macrophages that drive granuloma formation through a characteristic epithelioid transformation. Difficulties in imaging within intact animals as well as the inherent caveats of in vitro assembly models have severely limited the study and experimental manipulation of mature granulomas. Here we describe a new ex vivo granuloma culture technique, wherein mature, fully organized granulomas are microdissected and maintained in three-dimensional culture. This approach, in which granulomas retain key bacterial and host characteristics, enables high-resolution microscopy of granuloma macrophage dynamics, including epithelioid macrophage motility and granuloma consolidation. Through mass spectrometry, we find active production of key phosphotidylinositol species identified previously in human granulomas. We describe a method to transfect isolated granulomas, enabling genetic manipulation. In addition, we provide proof-of-concept for host-directed small molecule screens, identifying PKC signaling as an important regulator of granuloma macrophage organization.

Rifampin vs. rifapentine: what is the preferred rifamycin for tuberculosis?

INTRODUCTION

One-third of the world's population is infected with Mycobacterium tuberculosis (M.tb.). Latent tuberculosis infection (LTBI) can progress to tuberculosis disease, the leading cause of death by infection. Rifamycin antibiotics, like rifampin and rifapentine, have unique sterilizing activity against M.tb. What are the advantages of each for LTBI or tuberculosis treatment? Areas covered: We review studies assessing the pharmacokinetics (PK), pharmacodynamics (PD), drug interaction risk, safety, and efficacy of rifampin and rifapentine and provide basis for comparing them. Expert commentary: Rifampin has shorter half-life, higher MIC against M.tb, lower protein binding, and better distribution into cavitary contents than rifapentine. Drug interactions for the two drugs maybe similar in magnitude. For LTBI, rifapentine is effective as convenient, once-weekly, 12-week course of treatment. Rifampin is also effective for LTBI, but must be given daily for four months, therefore, drug interactions are more problematic. For drug-sensitive tuberculosis disease, rifampin remains the standard of care. Safety profile of rifampin is better-described; adverse events differ somewhat for the two drugs. The registered once-weekly rifapentine regimen is inadequate, but higher doses of either drugs may shorten the treatment duration required for effective management of TB. Results of clinical trials evaluating high-dose rifamycin regimens are eagerly awaited.

De Novo Emergence of Genetically Resistant Mutants of Mycobacterium tuberculosis from the Persistence Phase Cells Formed against Antituberculosis Drugs In Vitro

Bacterial persisters are a subpopulation of cells that can tolerate lethal concentrations of antibiotics. However, the possibility of the emergence of genetically resistant mutants from antibiotic persister cell populations, upon continued exposure to lethal concentrations of antibiotics, remained unexplored. In the present study, we found that Mycobacterium tuberculosis cells exposed continuously to lethal concentrations of rifampin (RIF) or moxifloxacin (MXF) for prolonged durations showed killing, RIF/MXF persistence, and regrowth phases. RIF-resistant or MXF-resistant mutants carrying clinically relevant mutations in the rpoB or gyrA gene, respectively, were found to emerge at high frequency from the RIF persistence phase population. A Luria-Delbruck fluctuation experiment using RIF-exposed M. tuberculosis cells showed that the rpoB mutants were not preexistent in the population but were formed de novo from the RIF persistence phase population. The RIF persistence phase M. tuberculosis cells carried elevated levels of hydroxyl radical that inflicted extensive genome-wide mutations, generating RIF-resistant mutants. Consistent with the elevated levels of hydroxyl radical-mediated genome-wide random mutagenesis, MXF-resistant M. tuberculosis gyrA de novo mutants could be selected from the RIF persistence phase cells. Thus, unlike previous studies, which showed emergence of genetically resistant mutants upon exposure of bacteria for short durations to sublethal concentrations of antibiotics, our study demonstrates that continuous prolonged exposure of M. tuberculosis cells to lethal concentrations of an antibiotic generates antibiotic persistence phase cells that form a reservoir for the generation of genetically resistant mutants to the same antibiotic or another antibiotic. These findings may have clinical significance in the emergence of drug-resistant tubercle bacilli.

New tuberculosis drug leads from naturally occurring compounds

Tuberculosis (TB) continues to be a significant cause of mortality and morbidity worldwide. An estimated 2 billion individuals are infected with Mycobacterium tuberculosis and annually there are approximately 10 million new cases of clinical TB and 1.5 million deaths. Currently available drugs and vaccines have had no significant impact on TB control. In addition, the emergence of drug resistant TB is considered a public health crisis, with some strains now resistant to all available drugs. Unfortunately, the growing burden of antibiotic resistance is coupled with decreased effort in the development of new antibiotics. Natural sources are attractive starting points in the search for anti-tubercular drugs because they are extremely rich in chemical diversity and have privileged antimicrobial activity. This review will discuss recent advances in the development of TB drug leads from natural products, with a particular focus on anti-mycobacterial compounds in late-stage preclinical and clinical development.

Rifapentine for the treatment of latent tuberculosis

INTRODUCTION

The goal of this article is to review the use of rifapentine in the treatment of latent tuberculosis infection (LTBI). Controlling LTBI is an important part of the global strategy to end the spread of tuberculosis. Rifapentine's potent sterilizing effect against Mycobacterium tuberculosis combined with its long half-life make it an attractive LTBI treatment option. Areas covered: A systematic literature search of Pubmed using the terms 'rifapentine' and 'tuberculosis' was performed. Articles identified were cross-referenced for other relevant publications. The mechanisms of action and resistance, pharmacokinetic and pharmacodynamics, potential drug interactions and side effects are discussed. Expert commentary: Rifapentine in combination with isoniazid for twelve weeks is the best available option for treating latent TB in the majority of patients in the United States due to its favorable safety profile and the increased likelihood of completing therapy. Currently, rifapentine is not registered or available in other countries.

Optimizing the clinical pharmacology of tuberculosis medications

Tuberculosis (TB) treatment has changed little in the past 40 years. The current standard therapy requires four drugs for 2 months followed by two drugs for 4 months. This "short-course" regimen is not based on optimized pharmacokinetic and pharmacodynamic properties, but empiric evidence. A review of existing data suggests that pharmacokinetic variability with isoniazid and rifampin is greater than previously thought, and that efficacy is not as good as traditionally reported. Adding new drugs to the current regimen will be costly and time-consuming. Maximizing the efficacy of the current medications is a less expensive and more feasible option. This article reviews the current potential of the first-line TB drugs (rifamycins, isoniazid, pyrazinamide, and ethambutol) as well as the fluoroquinolones to introduce a true short-course TB regimen.

A multi-scale approach to designing therapeutics for tuberculosis

Approximately one third of the world's population is infected with Mycobacterium tuberculosis. Limited information about how the immune system fights M. tuberculosis and what constitutes protection from the bacteria impact our ability to develop effective therapies for tuberculosis. We present an in vivo systems biology approach that integrates data from multiple model systems and over multiple length and time scales into a comprehensive multi-scale and multi-compartment view of the in vivo immune response to M. tuberculosis. We describe computational models that can be used to study (a) immunomodulation with the cytokines tumor necrosis factor and interleukin 10, (b) oral and inhaled antibiotics, and

Heterogeneous disease progression and treatment response in a C3HeB/FeJ mouse model of tuberculosis

Mice are the most commonly used species for non-clinical evaluations of drug efficacy against tuberculosis (TB). Unlike commonly used strains, C3HeB/FeJ mice develop caseous necrosis in the lung, which might alter the representation of drug efficacy in a way that is more like human TB. Because the development of such pathology requires time, we investigated the effect of infection incubation period on the activity of six drugs in C3HeB/FeJ and BALB/c mice. Mice were aerosol infected and held for 6, 10 or 14 weeks before receiving therapy with rifampin (RIF), rifapentine (RPT), pyrazinamide (PZA), linezolid (LZD), sutezolid (PNU) or metronidazole (MTZ) for 4-8 weeks. Outcomes included pathological assessments, pH measurements of liquefied caseum and assessment of colony-forming unit (CFU) counts from lung cultures. Remarkable heterogeneity in the timing and extent of disease progression was observed in C3HeB/FeJ mice, largely independent of incubation period. Likewise, drug efficacy in C3HeB/FeJ mice was not affected by incubation period. However, for PZA, LZD and PNU, dichotomous treatment effects correlating with the presence or absence of large caseous lesions were observed. In the case of PZA, its poor activity in the subset of C3HeB/FeJ mice with large caseous lesions might be explained by the pH of 7.36±0.09 measured in liquefied caseum. This study highlights the potential value of C3HeB/FeJ mice for non-clinical efficacy testing, especially for investigating the interaction of lesion pathology and drug effect. Careful use of this model could enhance the bridging of non-clinical results with clinical outcomes.

Summary: C3HeB/FeJ mice develop a wide range of lesion types that alter drug response in a way that might better inform tuberculosis drug development.

A computational tool integrating host immunity with antibiotic dynamics to study tuberculosis treatment

While active tuberculosis (TB) is a treatable disease, many complex factors prevent its global elimination. Part of the difficulty in developing optimal therapies is the large design space of antibiotic doses, regimens and combinations. Computational models that capture the spatial and temporal dynamics of antibiotics at the site of infection can aid in reducing the design space of costly and time-consuming animal pre-clinical and human clinical trials. The site of infection in TB is the granuloma, a collection of immune cells and bacteria that form in the lung, and new data suggest that penetration of drugs throughout granulomas is problematic. Here we integrate our computational model of granuloma formation and function with models for plasma pharmacokinetics, lung tissue pharmacokinetics and pharmacodynamics for two first line anti-TB antibiotics. The integrated model is calibrated to animal data. We make four predictions. First, antibiotics are frequently below effective concentrations inside granulomas, leading to bacterial growth between doses and contributing to the long treatment periods required for TB. Second, antibiotic concentration gradients form within granulomas, with lower concentrations toward their centers. Third, during antibiotic treatment, bacterial subpopulations are similar for INH and RIF treatment: mostly intracellular with extracellular bacteria located in areas non-permissive for replication (hypoxic areas), presenting a slowly increasing target population over time. Finally, we find that on an individual granuloma basis, pre-treatment infection severity (including bacterial burden, host cell activation and host cell death) is predictive of treatment outcome.

An update on the use of rifapentine for tuberculosis therapy

INTRODUCTION

Tuberculosis (TB) remains rampant throughout the world, in large part due to the lengthy treatment times of current therapeutic options. Rifapentine, a rifamycin antibiotic, is currently approved for intermittent dosing in the treatment of TB. Recent animal studies have shown that more frequent administration of rifapentine could shorten treatment times, for both latent and active TB infection. However, these results were not replicated in a subsequent human clinical trial.

AREAS COVERED

This review analyses the evidence for more frequent administration of rifapentine and the reasons for the apparent lack of efficacy in shortening treatment times in human patients. Inhaled delivery is discussed as a potential option to achieve the therapeutic effect of rifapentine by overcoming the barriers associated with oral administration of this drug. Avenues for developing an inhalable form of rifapentine are also presented.

EXPERT OPINION

Rifapentine is a promising active pharmaceutical ingredient with potential to accelerate treatment of TB if delivered by inhaled administration. Progression of current fundamental work on inhaled anti-tubercular therapies to human clinical trials is essential for determining their role in future treatment regimens. While the ultimate goal for global TB control is a vaccine, a short and effective treatment option is equally crucial.

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.

Rifapentine is not more active than rifampin against chronic tuberculosis in guinea pigs

Rifamycins are key sterilizing drugs in the current treatment of active tuberculosis (TB). Daily dosing of rifapentine (P), a potent rifamycin with high intracellular accumulation, in place of rifampin (R) in the standard antitubercular regimen significantly shortens the duration of treatment needed to prevent relapse in a murine model of active TB. We undertook the current study to compare directly the activities of human-equivalent doses of P and R in a guinea pig model of chronic TB, in which bacilli are predominantly extracellular within human-like necrotic granulomas. Hartley strain guinea pigs were aerosol infected with ~200 bacilli of Mycobacterium tuberculosis H37Rv, and treatment given 5 days/week was initiated 6 weeks later. R at 100 mg/kg of body weight and P at 100 mg/kg were given orally alone or in combination with isoniazid (H) at 60 mg/kg and pyrazinamide (Z) at 300 mg/kg. Culture-positive relapse was assessed in subgroups of guinea pigs after completion of 1 and 2 months of treatment. Human-equivalent doses of R and P showed equivalent bactericidal activity when used alone and in combination therapy. In guinea pigs treated with rifampin, isoniazid, and pyrazinamide (RHZ) or PHZ, microbiological relapse occurred in the lungs of 8/10 animals treated for 1 month and in 0/10 animals treated for 2 months. Substitution of P for R in the standard antitubercular regimen did not shorten the time to cure in this guinea pig model of chronic TB. Data from ongoing clinical trials comparing the activity of these two drugs are awaited to determine the relevance of the guinea pig TB model in preclinical drug screening.

New drugs for tuberculosis treatment

Available data on anti-tuberculosis drug research reveal different properties of the agents and provoke speculation about future directions. Higher doses of the rifamycins are promising and are currently being evaluated in regimens of shorter duration that the isoniazid plus rifampin-based, six-to-nine month-course therapy. Moxifloxacin and gatifloxacin might shorten tuberculosis treatment as well, possibly in combination with rifapentine, while SQ109 could enhance the activity of rifampin-containing regimens. On the other hand, co-administration of moxifloxacin and PA-824 could be active against latent tuberculosis, whereas linezolid, PA-824 and TMC207 are candidates for a rifampin-free regimen in multidrug-resistant and extensively-resistant tuberculosis. Unfortunately, shorter than existent treatment regimens based on the new agents discussed here are likely to take at least another decade to be fully developed and implemented in clinical practice.

Mycobacterium tuberculosis uses host triacylglycerol to accumulate lipid droplets and acquires a dormancy-like phenotype in lipid-loaded macrophages

Two billion people are latently infected with Mycobacterium tuberculosis (Mtb). Mtb-infected macrophages are likely to be sequestered inside the hypoxic environments of the granuloma and differentiate into lipid-loaded macrophages that contain triacylglycerol (TAG)-filled lipid droplets which may provide a fatty acid-rich host environment for Mtb. We report here that human peripheral blood monocyte-derived macrophages and THP-1 derived macrophages incubated under hypoxia accumulate Oil Red O-staining lipid droplets containing TAG. Inside such hypoxic, lipid-loaded macrophages, nearly half the Mtb population developed phenotypic tolerance to isoniazid, lost acid-fast staining and accumulated intracellular lipid droplets. Dual-isotope labeling of macrophage TAG revealed that Mtb inside the lipid-loaded macrophages imports fatty acids derived from host TAG and incorporates them intact into Mtb TAG. The fatty acid composition of host and Mtb TAG were nearly identical suggesting that Mtb utilizes host TAG to accumulate intracellular TAG. Utilization of host TAG by Mtb for lipid droplet synthesis was confirmed when fluorescent fatty acid-labeled host TAG was utilized to accumulate fluorescent lipid droplets inside the pathogen. Deletion of the Mtb triacylglycerol synthase 1 (tgs1) gene resulted in a drastic decrease but not a complete loss in both radiolabeled and fluorescent TAG accumulation by Mtb suggesting that the TAG that accumulates within Mtb is generated mainly by the incorporation of fatty acids released from host TAG. We show direct evidence for the utilization of the fatty acids from host TAG for lipid metabolism inside Mtb. Taqman real-time PCR measurements revealed that the mycobacterial genes dosR, hspX, icl1, tgs1 and lipY were up-regulated in Mtb within hypoxic lipid loaded macrophages along with other Mtb genes known to be associated with dormancy and lipid metabolism.

Two billion people are latently infected with Mycobacterium tuberculosis (Mtb). Cure and possible eradication of tuberculosis are limited by the lack of availability of any drug that can kill dormant Mtb. Understanding of the processes critical for dormancy and a reliable dormancy model suitable for high throughput screening of chemicals will help to discover drugs that can kill dormant Mtb. Storage of lipids for utilization as energy source is critically needed for dormancy. In the human lung, Mtb-infected macrophages are sequestered inside the hypoxic environments of the physical enclosure called granuloma in which Mtb becomes dormant. None of the currently used cell culture models of Mtb infection mimic this situation. We developed a model that mimics the environment inside the human granuloma by incubating Mtb-infected macrophages under hypoxia. We found that, under these conditions, macrophages accumulate lipid droplets and Mtb within these macrophages acquire a dormancy phenotype. We report how the pathogen inside the macrophages utilizes the host lipids to store lipids within the pathogen and acquire the hallmark traits of dormant Mtb. Thus, our novel model of Mtb dormancy may enable better understanding of the metabolic processes vital for the dormant pathogen and help to discover drugs that can kill latent pathogens.

Intracellular pharmacokinetics of telithromycin, a ketolide antibiotic, in alveolar macrophages

OBJECTIVES

Telithromycin, a ketolide antibiotic, has an antibacterial range that covers intracellular parasitic pathogens that survive or multiply intracellularly in alveolar macrophages. The intracellular pharmacokinetics of TEL in alveolar macrophages was evaluated in vitro.

METHODS

Telithromycin (50 microm) was applied to NR8383 as cultured alveolar macrophages, followed by incubation at 37 degrees C or 4 degrees C. After incubation, the amount of telithromycin in cells was determined.

KEY FINDINGS

Telithromycin exhibited high accumulation in NR8383 and its intracellular accumulation was temperature dependent. Also, telithromycin distributed to the organelles and cytosol in NR8383 and, in particular, it accumulated in the acidic organelle compartments.

CONCLUSIONS

This study suggests that the high accumulation of telithromycin in NR8383 is due to its high influx via active transport systems and trapping in acidic organelles, such as lysosomes. Moreover, this study provides important information for optimizing the treatment of respiratory intracellular parasitic infections based on the intracellular pharmacokinetics of antibiotics and parasitic sites.

Rifamycins--obstacles and opportunities

With nearly one-third of the global population infected by Mycobacterium tuberculosis, TB remains a major cause of death (1.7 million in 2006). TB is particularly severe in parts of Asia and Africa where it is often present in AIDS patients. Difficulties in treatment are exacerbated by the 6-9 month treatment times and numerous side effects. There is significant concern about the multi-drug-resistant (MDR) strains of TB (0.5 million MDR-TB cases worldwide in 2006). The rifamycins, long considered a mainstay of TB treatment, were a tremendous breakthrough when they were developed in the 1960's. While the rifamycins display many admirable qualities, they still have a number of shortfalls including: rapid selection of resistant mutants, hepatotoxicity, a flu-like syndrome (especially at higher doses), potent induction of cytochromes P450 (CYP) and inhibition of hepatic transporters. This review of the state-of-the-art regarding rifamycins suggests that it is quite possible to devise improved rifamycin analogs. Studies showing the potential of shortening the duration of treatment if higher doses could be tolerated, also suggest that more potent (or less toxic) rifamycin analogs might accomplish the same end. The improved activity against rifampin-resistant strains by some analogs promises that further work in this area, especially if the information from co-crystal structures with RNA polymerase is applied, should lead to even better analogs. The extensive drug-drug interactions seen with rifampin have already been somewhat ameliorated with rifabutin and rifalazil, and the use of a CYP-induction screening assay should serve to efficiently identify even better analogs. The toxicity due to the flu-like syndrome is an issue that needs effective resolution, particularly for analogs in the rifalazil class. It would be of interest to profile rifalazil and analogs in relation to rifampin, rifapentine, and rifabutin in a variety of screens, particularly those that might relate to hypersensitivity or immunomodulatory processes.

Evaluation of an intracellular pharmacokinetic in vitro infection model as a tool to assess tuberculosis therapy

In vitro intracellular infection models have been used to evaluate drug therapy against Mycobacterium tuberculosis; however, they do not simulate human pharmacokinetics. This study demonstrates the intracellular and extracellular killing activity of antimycobacterial drugs in a pharmacokinetic intracellular in vitro model. The pharmacokinetic parameters of levofloxacin, rifampicin and isoniazid were controlled in the central chamber; drug passively diffused into the cell culture inserts and then into the macrophages. In the pharmacokinetic model, the rates of killing observed were faster than other in vitro methods and allowed for a higher initial inoculum to be utilised. The pharmacokinetic model more closely mimics in vivo conditions than other in vitro systems and is a new instrument for evaluating the activity of antimycobacterial agents.

Pharmacokinetic Considerations in the Treatment of Tuberculosis in Patients with Renal Failure

Tuberculosis is re-emerging in patients with altered immune status, such as those with chronic renal failure. Clinicians should thus be aware of the pharmacokinetics and dosage adjustment of antitubercular drugs in patients with renal insufficiency. Among patients with renal insufficiency, those who are dialysed should be treated with special care. Indeed, dosage should always be closely adjusted in these patients and potential removal by dialysis must be taken into account. However reliable the dosage adjustment recommendations are for these drugs in patients with renal failure, further pharmacokinetic investigations need to be performed, especially in dialysis patients in whom the influence of haemodialysis and continuous ambulatory peritoneal dialysis on drug pharmacokinetics needs to be detailed. In the meantime, it could be generally advised to administer all antitubercular drugs after the haemodialysis session, even though some drugs are known to be non-dialysable.

Pharmacokinetics of Rifapentine at 600, 900, and 1,200 mg during Once-Weekly Tuberculosis Therapy

The pharmacokinetics of rifapentine at 600, 900, and 1,200 mg were studied during once-weekly continuation phase therapy in 35 patients with tuberculosis. Mean area under the plasma concentration-time curve (AUC(0-infinity)) increased significantly with dose (rifapentine AUC(0- infinity): 296, 410, and 477 microg.hour/ml at 600, 900, and 1,200 mg, respectively; p = 0.02 by linear regression). In multivariate stepwise regression analyses, AUC(0-infinity) values for rifapentine and the active 25-desacetyl metabolite were associated with drug dose and plasma albumin concentration, and were lower among men and among white individuals. Fifty-four percent of patients had total (free and protein-bound) plasma concentrations of rifapentine and of desacetyl rifapentine detected for more than 36 hours after clearance of concurrently administered isoniazid. Serious adverse effects of therapy in these study patients were infrequent (1 of 35 cases; 3%) and not linked with higher rifapentine AUC(0-infinity) or peak concentration. The present pharmacokinetic study supports further trials to determine the optimal rifapentine dose for treatment of tuberculosis.

Effect of Sex and AIDS Status on the Plasma and Intrapulmonary Pharmacokinetics of Rifampicin

OBJECTIVE

To compare the steady-state plasma and intrapulmonary concentrations of oral rifampicin (rifampin) in men and women with and without AIDS.

DESIGN

Prospective nonblinded pharmacokinetic study.

PARTICIPANTS

Ten men with AIDS, ten men without AIDS, ten women with AIDS, and ten women without AIDS.

METHODS

Rifampicin 600 mg was administered orally once daily for 5 days to 40 adult volunteers. Blood was obtained 2 hours after the last dose and at the time of bronchoalveolar lavage (BAL) performed 4 hours after the last dose. Rifampicin was measured in plasma, epithelial lining fluid (ELF) and alveolar cells. Standardised BAL was performed without systemic sedation. The volume of ELF was calculated by the urea dilution method, and alveolar cells were recovered by a standardised centrifugation technique. The volume of alveolar cells was calculated from the cell count and differential performed on the BAL fluid. Rifampicin was measured by high-performance liquid chromatography.

RESULTS

Sex or AIDS status had no effect on plasma concentrations of rifampicin at 2 hours, 4 hours, or in ELF. Plasma concentrations (mean +/- SD) of rifampicin at 2 hours (9.15 +/- 5.4 mg/L) were not significantly different (p > 0.05) from those at 4 hours (9.10 +/- 5.6 mg/L) following the last dose. The ELF concentration was 2.0 +/- 1.6 mg/L with a range of 0-7.3 mg/L and the ELF/plasma ratio at 4 hours was 0.2 +/- 0.2. Rifampicin was not detectable in ELF in eight subjects (three with AIDS and five without AIDS) or in alveolar cells in three subjects without AIDS. There was no significant effect of AIDS on alveolar cell concentrations of rifampicin. Alveolar cell concentrations of rifampicin were significantly greater in women (13.9 +/- 6.7 mg/L) than in men (6.6 +/- 4.1 mg/L) [p = 0.0003]. Alveolar cell rifampicin concentrations were 78% greater in smoking women (17.8 +/- 7.0 mg/L) than in nonsmoking women (10.0 +/- 2.4 mg/L), but the difference was not significant (p > 0.05). CD4+ cell counts in the AIDS subjects were not correlated with the concentrations of rifampicin in plasma, ELF or alveolar cells.

CONCLUSIONS

The absorption of oral rifampicin was not affected by sex or AIDS. Plasma and alveolar cell concentrations were not significantly different, were both greater than ELF concentrations, and were adequate to inhibit Mycobacterium tuberculosis. Considerable interpatient variability was detected despite witnessed drug administration. The clinical significance of these findings is unknown but merits further investigation.

Comparative pharmacokinetics and pharmacodynamics of the rifamycin antibacterials

The rifamycin antibacterials, rifampicin (rifampin), rifabutin and rifapentine, are uniquely potent in the treatment of patients with tuberculosis and chronic staphylococcal infections. Absorption is variably affected by food; the maximal concentration of rifampicin is decreased by food, whereas rifapentine absorption is increased in the presence of food. The rifamycins are well-known inducers of enzyme systems involved in the metabolism of many drugs, most notably those metabolised by cytochrome P450 (CYP) 3A. The relative potency of the rifamycins as CYP3A inducers is rifampin > rifapentine > rifabutin; rifabutin is also a CYP3A substrate. The antituberculosis activity of rifampicin is decreased by a modest dose reduction from 600 to 450mg. This somewhat surprising finding may be due to the binding of rifampicin to serum proteins, limiting free, active concentrations of the drug. However, increasing the administration interval (after the first 2 to 8 weeks of therapy) has little effect on the sterilising activity of rifampicin, suggesting that relatively brief exposures to a critical concentration of rifampicin are sufficient to kill intermittently metabolising mycobacterial populations. The high protein binding of rifapentine (97%) may explain the suboptimal efficacy of the currently recommended dose of this drug. The toxicity of rifampicin is related to dose and administration interval, with increasing rates of presumed hypersensitivity with higher doses combined with administration frequency of once weekly or less. Rifabutin toxicity is related to dose and concomitant use of CYP3A inhibitors. The rifamycins illustrate the complexity of predicting the pharmacodynamics of treatment of an intracellular pathogen with the capacity for dormancy.

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.

Single-dose intrapulmonary pharmacokinetics of rifapentine in normal subjects

The intrapulmonary pharmacokinetics of rifapentine were studied in 30 volunteers who received a single, oral dose of rifapentine (600 mg). Subgroups of five subjects each underwent bronchoscopy and bronchoalveolar lavage (BAL) at timed intervals following drug administration. Drug concentrations, including the concentration of the primary metabolite 25-desacetyl rifapentine, were determined in plasma, BAL fluid, and alveolar cells (AC) by high-pressure liquid chromatography. The concentrations in epithelial lining fluid (ELF) were calculated by the urea diffusion method. The concentration-time data were fit to two-compartment (plasma) or one-compartment (AC and ELF) models. The peak concentrations in plasma, ELF, and AC, 26.2, 3. 7, and 5.3 microg/ml, respectively, occurred at 5, 5, and 7 h after drug administration, respectively. The half-lives and areas under the curve for plasma, ELF, and AC were 18.3 h and 520 microg. h/ml, 20.8 h and 111 microg. h/ml, and 13.0 h and 133 microg. h/ml, respectively. Although the intrapulmonary rifapentine concentrations were less than the plasma rifapentine concentrations at all time periods, they remained above the proposed breakpoint for M. tuberculosis (0.5 microg/ml) for the 48-h observation period. These data provide a pharmacokinetic rationale for extended-interval dosing. The optimum dosing regimen for rifapentine will have to be determined by controlled clinical trials.

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 administration 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. Adverse events of rifapentine may occur less frequently at the currently recommended 600-mg dose 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 non-adherence. 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 whether 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.

Activities of poloxamer CRL-1072 against Mycobacterium avium in macrophage culture and in mice

Earlier studies reported that certain large hydrophobic poloxamer surfactants were able to inhibit the growth of Mycobacterium avium-M. intracellulare complex (MAI) in broth and to produce synergistic enhancement of the activity of rifampin. CRL-1072 was synthesized to have an optimal structure for antimicrobic effects and greater purity. Its MIC for MAI in broth was greater than 100 microg/ml. Surprisingly, its MIC for MAI growing in human U937 monocytoid cells was much lower, 5 microg/ml. A still lower concentration, 0.1 microg/ml, produced synergistic enhancement of the activities of clarithromycin, rifampin, amikacin, streptomycin, and clindamycin, but not isoniazid, against MAI infecting monocytoid cells. Mice tolerated injection of doses of CRL-1072 as high as 125 mg/kg of body weight. Pharmacokinetic analysis revealed that the copolymer had an elimination half-life of 60 h and suggested dosing regimens that might produce therapeutic concentrations in tissue. In a mouse model of acute MAI infection, CRL-1072 significantly enhanced the bactericidal activities of clarithromycin and rifampin when it was administered at 1.0 mg/kg intravenously (i.v.) three times per week. CRL-1072 given i.v. or orally also enhanced the bactericidal activity of clindamycin against MAI.

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.

Rifapentine pharmacokinetics in adolescents

OBJECTIVE

Determination of rifapentine pharmacokinetics in healthy adolescent children.

DESIGN

Prospective Phase II clinical trial.

SETTING

Clinical research center within a university children's hospital.

PATIENTS

Twelve subjects ranging in age from 12 to 15 years, male and female.

INTERVENTIONS

A single oral dose of rifapentine was administered to healthy adolescent volunteers, 450 mg if <45 kg or 600 mg if > or =45 kg. Blood was collected at serial intervals (0, 2, 3, 4, 5, 6, 8, 12, 18, 24, 48 and 72 h postdose). Subjects were observed for adverse effects during the period of study.

MEASUREMENTS

High pressure liquid chromatography was used to measure the plasma concentration of rifapentine and 25-desacetyl rifapentine in each blood sample. For each subject a plot of mean plasma concentration vs. time data for rifapentine and its metabolite (i.e. 25-desacetyl rifapentine) were created. Subsequently model-independent methods were used to determine the pharmacokinetic profiles for each subject.

RESULTS

All subjects tolerated rifapentine without adverse effects. The 2-h postdose plasma concentrations of rifapentine (6.59 to 9.05 microg/ml) and 25-desacetyl rifapentine (0.57 to 2.64 microg/ml) far exceeded the MIC of Mycobacterium tuberculosis to rifapentine (approximately 0.12 microg/ml). The combination of a high Cmax (rifapentine, 9.95 to 18.63 microg/ml; 25-desacetyl rifapentine, 3.73 to 7.46 microg/ml) and lengthy terminal elimination phase t1/2 (rifapentine, 10 to 23 h; 25-desacetyl rifapentine, 14 to 35 h) resulted in potentially effective plasma concentrations of both compounds that persisted for at least 48 h in most subjects.

CONCLUSIONS

A well-tolerated oral rifapentine dose produced rapid and sustained plasma drug concentrations in adolescents that should effectively treat infections caused by M. tuberculosis. Rifapentine pharmacokinetics appears to be similar in adolescent and adult populations.

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.

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.