Pharmacokinetics-pharmacodynamics of rifampin in an aerosol infection model of tuberculosis

A Systematic Review on the Effect of HIV Infection on the Pharmacokinetics of First-Line Tuberculosis Drugs

Introduction

Contrasting findings have been published regarding the effect of human immunodeficiency virus (HIV) on tuberculosis (TB) drug pharmacokinetics (PK).

Objectives

The aim of this systematic review was to investigate the effect of HIV infection on the PK of the first-line TB drugs (FLDs) rifampicin, isoniazid, pyrazinamide and ethambutol by assessing all published literature.

Methods

Searches were performed in MEDLINE (through PubMed) and EMBASE to find original studies evaluating the effect of HIV infection on the PK of FLDs. The included studies were assessed for bias and clinical relevance. PK data were extracted to provide insight into the difference of FLD PK between HIV-positive and HIV-negative TB patients. This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement and its protocol was registered at PROSPERO (registration number CRD42017067250).

Results

Overall, 27 studies were eligible for inclusion. The available studies provide a heterogeneous dataset from which consistent results could not be obtained. In both HIV-positive and HIV-negative TB groups, rifampicin (13 of 15) and ethambutol (4 of 8) peak concentration (C_max) often did not achieve the minimum reference values. More than half of the studies (11 of 20) that included both HIV-positive and HIV-negative TB groups showed statistically significantly altered FLD area under the concentration–time curve and/or C_max for at least one FLD.

Conclusions

HIV infection may be one of several factors that reduce FLD exposure. We could not make general recommendations with respect to the role of dosing. There is a need for consistent and homogeneous studies to be conducted.

Personalized Tuberculosis Treatment Through Model-Informed Dosing of Rifampicin

BACKGROUND AND OBJECTIVE

This study proposes a model-informed approach for therapeutic drug monitoring (TDM) of rifampicin to improve tuberculosis (TB) treatment.

METHODS

Two datasets from pulmonary TB patients were used: a pharmacokinetic study (34 patients, 373 samples), and TDM data (96 patients, 391 samples) collected at Radboud University Medical Center, The Netherlands. Nine suitable population pharmacokinetic models of rifampicin were identified in the literature and evaluated on the datasets. A model developed by Svensson et al. was found to be the most suitable based on graphical goodness of fit, residual diagnostics, and predictive performance. Prediction of individual area under the concentration-time curve from time zero to 24 h (AUC₂₄) and maximum concentration (C_max) employing various sampling strategies was compared with a previously established linear regression TDM strategy, using sampling at 2, 4, and 6 h, in terms of bias and precision (mean error [ME] and root mean square error [RMSE]).

RESULTS

A sampling strategy using 2- and 4-h blood collection was selected to be the most suitable. The bias and precision of the two strategies were comparable, except that the linear regression strategy was more biased in prediction of the AUC₂₄ than the model-informed approach (ME of 9.9% and 1.5%, respectively). A comparison of resulting dose advice, using predictions on a simulated dataset, showed no significant difference in sensitivity or specificity between the two methods. The model was successfully implemented in the InsightRX precision dosing platform.

CONCLUSION

Blood sampling at 2 and 4 h, combined with model-based prediction, can be used instead of the currently used linear regression strategy, shortening the sampling by 2 h and one sampling point without performance loss while simultaneously offering flexibility in sampling times.

Mathematical model and tool to explore shorter multi-drug therapy options for active pulmonary tuberculosis

Standard treatment for active tuberculosis (TB) requires drug treatment with at least four drugs over six months. Shorter-duration therapy would mean less need for strict adherence, and reduced risk of bacterial resistance. A system pharmacology model of TB infection, and drug therapy was developed and used to simulate the outcome of different drug therapy scenarios. The model incorporated human immune response, granuloma lesions, multi-drug antimicrobial chemotherapy, and bacterial resistance. A dynamic population pharmacokinetic/pharmacodynamic (PK/PD) simulation model including rifampin, isoniazid, pyrazinamide, and ethambutol was developed and parameters aligned with previous experimental data. Population therapy outcomes for simulations were found to be generally consistent with summary results from previous clinical trials, for a range of drug dose and duration scenarios. An online tool developed from this model is released as open source software. The TB simulation tool could support analysis of new therapy options, novel drug types, and combinations, incorporating factors such as patient adherence behavior.

A comprehensive in-silico model of pulmonary tuberculosis successfully predicted previous clinical trials and could simulate future therapeutics.

Melaleuca armillaris Essential Oil in Combination With Rifaximin Against Staphylococcus aureus Isolated of Dairy Cows

Staphylococcus aureus is the major subclinical mastitis-causing pathogen in dairy cows. In some European and Latin American countries, rifaximin (RIF) is a commonly used therapy at drying off. Phytotherapeutics are alternatives for the treatment of infectious diseases. Melaleuca armillaris essential oil (EO) has been reported as a good antimicrobial against S. aureus. The aim of this work was to investigate, in vitro, the combined effect of EO and RIF to identify a synergic interaction against S. aureus in order to obtain enough information for subsequent pharmacokinetic/pharmacodynamic studies. The minimum inhibitory concentrations (MIC) for RIF, EO, and combinations of these against S. aureus strains were determined at pH 7.4, 6.5, and 5.0, representing intracellular conditions where S. aureus is usually located. The fractional inhibitory concentration index (FIC) and the index of antibacterial activity (E) were evaluated. The MIC of EO at pH 7.4 was 25-12.5 μL/mL and decreased with the acidity of the medium. RIF presented a high antimicrobial activity (0.032 μg/mL) against S. aureus regardless of the pH conditions. Combining RIF with EO, we found a synergic effect. A mix of 0.004 μg/mL of RIF and 12.5 μL/mL of EO led to a virtual eradication effect against wild-type strains at pH 7.4. Media acidification improves the EO/RIF activity, so EO would be a good adjuvant for RIF to treat staphylococcal infections and decrease antimicrobial resistance.

Pharmacokinetics/Pharmacodynamics (PK/PD) of Ciprofloxacin in the Complicated Urinary Tract Infection (cUTI) Model in Diabetic Mice

Background:

The translation of Pharmacokinetics (PK)/Pharmacodynamics (PD) from preclinical models to the clinic has not been studied in detail for drugs used to treat complicated urinary tract infections (cUTI).

Objective:

The PK/PD of Ciprofloxacin (CIP), a drug used to treat cUTI, was evaluated in a mouse model of cUTI infected with Escherichia coli, and compared with clinical PK/PD in cUTI patients.

Methods:

Streptozotocin induced diabetic female BALB/c mice were infected transurethrally with Escherichia coli. Four hours post infection, CIP oral doses of 3, 10, 30,100, and 300 mg/kg, were administered as single doses (for PK and dose response) and repeated doses (PD and PK/PD). Bacterial burden in kidneys, bladder, urine, body temperature, and other clinical signs were assessed twenty-four hours post-treatment.

Results:

CIP displayed linear PK with dose proportional increase in Cmax and AUCinf in plasma. In PD time course studies, CIP showed rapid onset, intensity and duration of anti-bacterial effect in target tissues. In intrinsic PD studies, CIP showed a maximum effect at plasma AUC/MIC=1705 (300 mg/kg, twice daily) for bacterial load in bladder (r2=0.979), kidney (r2=0.951) and rectal temperature (r2=0.67). A plasma AUC/MIC ratio of 412 was associated with maximum PD effect of Imax=3.7 Log10CFU/bladder and Imax=1.97 Log10CFU/kidney. In dose fractionation studies, plasma AUC/MIC ratio showed highest correlation with efficacy in bladder (r2=0.77) and kidney (r2=0.80) followed by Cmax/MIC ratio in bladder (r2=0.68).

Conclusion:

Plasma AUC/MIC showed the highest correlation with the efficacy of Ciprofloxacin on E. coli in diabetic mice with cUTI.

Identification of Anti-tuberculosis Compounds From Aurone Analogs

The emergence of multidrug-resistant Mycobacterium tuberculosis (Mtb) strains has made tuberculosis (TB) control more difficult. Aurone derivatives have demonstrated promising anti-bacterial activities, but their effects against Mtb have not been thoroughly determined. In this study, we aimed to develop anti-TB compounds from aurone analogs. We used a fluorescent protein tdTomato labeled Mtb CDC1551 strain to screen 146 synthesized aurone derivatives for effective anti-TB compounds. The 9504, 9505, 9501, 9510, AA2A, and AA8 aurones inhibited the growth of Mtb with minimal inhibitory concentrations of 6.25, 12.5, 25, 25, 25, and 50 μM, respectively. We also examined cytotoxicities of the six leads against the human liver cell line HepG2, the primate kidney cell line Vero and human monocyte THP-1 derived macrophages. Three of the aurone leads (9504, 9501, and 9510) showed low cytotoxic effects on all three cell lines and high Mtb inhibitory efficacy (selectivity index > 10). Aurone 9504, 9501, AA2A, or AA8 significantly reduced the Mtb load in the lungs of infected mice after a 12-days treatment. We determined that the aurone leads inhibit Mtb chorismate synthase, an essential enzyme for aromatic acid synthesis. Our studies demonstrate the promise of synthetic aurones as novel anti-TB therapeutics.

Evaluation of current dosing guidance for oral rifampicin treatment in adult patients with osteoarticular infections

For management of osteoarticular infections, rifampicin appears to be the key antibiotic. We aimed to evaluate the actual rifampicin dosing regimens using a population pharmacokinetic model of rifampicin in patients with osteoarticular infections. A Monte Carlo simulation study was performed to simulate steady-state plasma concentrations for 1000 randomly sampled subjects using a total daily dose between 600 and 1200 mg (600 and 900 mg once daily, 450 and 600 mg twice daily, or 300 mg 3 times daily). When rifampicin was administered with fusidic acid, the pharmacokinetic/pharmacodynamic (PK/PD) target (area under the curve/minimum inhibitory concentration ≥952) was achieved with all tested dosing regimen, except 600 mg once daily for Staphylococcus epidermidis infections. Without coadministration of fusidic acid, none of tested dosing regimens achieved this PK/PD target. Most recommended drug-dosing regimens allow attaining the fixed area under the curve/minimum inhibitory concentration target for Staphylococcus aureus and coagulase-negative staphylococcal osteoarticular infections. In future studies, PK/PD target for osteoarticular infections in human should also be confirmed.

Both Pharmacokinetic Variability and Granuloma Heterogeneity Impact the Ability of the First-Line Antibiotics to Sterilize Tuberculosis Granulomas

Tuberculosis (TB) remains as one of the world's deadliest infectious diseases despite the use of standardized antibiotic therapies. Recommended therapy for drug-susceptible TB is up to 6 months of antibiotics. Factors that contribute to lengthy regimens include antibiotic underexposure in lesions due to poor pharmacokinetics (PK) and complex granuloma compositions, but it is difficult to quantify how individual antibiotics are affected by these factors and to what extent these impact treatments. We use our next-generation multi-scale computational model to simulate granuloma formation and function together with antibiotic pharmacokinetics and pharmacodynamics, allowing us to predict conditions leading to granuloma sterilization. In this work, we focus on how PK variability, determined from human PK data, and granuloma heterogeneity each quantitatively impact granuloma sterilization. We focus on treatment with the standard regimen for TB of four first-line antibiotics: isoniazid, rifampin, ethambutol, and pyrazinamide. We find that low levels of antibiotic concentration due to naturally occurring PK variability and complex granulomas leads to longer granuloma sterilization times. Additionally, the ability of antibiotics to distribute in granulomas and kill different subpopulations of bacteria contributes to their specialization in the more efficacious combination therapy. These results can inform strategies to improve antibiotic therapy for TB.

High-dose rifapentine with or without moxifloxacin for shortening treatment of pulmonary tuberculosis: Study protocol for TBTC study 31/ACTG A5349 phase 3 clinical trial

INTRODUCTION

Phase 2 clinical trials of tuberculosis treatment have shown that once-daily regimens in which rifampin is replaced by high dose rifapentine have potent antimicrobial activity that may be sufficient to shorten overall treatment duration. Herein we describe the design of an ongoing phase 3 clinical trial testing the hypothesis that once-daily regimens containing high dose rifapentine in combination with other anti-tuberculosis drugs administered for four months can achieve cure rates not worse than the conventional six-month treatment regimen.

METHODS/DESIGN

S31/A5349 is a multicenter randomized controlled phase 3 non-inferiority trial that compares two four-month regimens with the standard six-month regimen for treating drug-susceptible pulmonary tuberculosis in HIV-negative and HIV-positive patients. Both of the four-month regimens contain high-dose rifapentine instead of rifampin, with ethambutol replaced by moxifloxacin in one regimen. All drugs are administered seven days per week, and under direct observation at least five days per week. The primary outcome is tuberculosis disease-free survival at twelve months after study treatment assignment. A total of 2500 participants will be randomized; this gives 90% power to show non-inferiority with a 6.6% margin of non-inferiority.

DISCUSSION

This phase 3 trial formally tests the hypothesis that augmentation of rifamycin exposures can shorten tuberculosis treatment to four months. Trial design and standardized implementation optimize the likelihood of obtaining valid results. Results of this trial may have important implications for clinical management of tuberculosis at both individual and programmatic levels.

TRIAL REGISTRATION

NCT02410772. Registered 8 April 2015,https://www.clinicaltrials.gov/ct2/show/NCT02410772?term=02410772&rank=1.

Antitubercular nanocarrier monotherapy: Study of In Vivo efficacy and pharmacokinetics for rifampicin

Tuberculosis represents a major global health problem for which improved approaches are needed to shorten the course of treatment and to combat the emergence of resistant strains. The development of effective and safe nanobead-based interventions can be particularly relevant for increasing the concentrations of antitubercular agents within the infected site and reducing the concentrations in the general circulation, thereby avoiding off-target toxic effects. In this work, rifampicin, a first-line antitubercular agent, was encapsulated into biocompatible and biodegradable polyester-based nanoparticles. In a well-established BALB/c mouse model of pulmonary tuberculosis, the nanoparticles provided improved pharmacokinetics and pharmacodynamics. The nanoparticles were well tolerated and much more efficient than an equivalent amount of free rifampicin.

State of the art in cystic fibrosis pharmacology-Optimization of antimicrobials in the treatment of cystic fibrosis pulmonary exacerbations: I. Anti-methicillin-resistant Staphylococcus aureus (MRSA) antibiotics

Acute pulmonary exacerbations (APE) are a complication of cystic fibrosis (CF) and are associated with morbidity and mortality. Methicillin-resistant Staphylococcus aureus (MRSA) is one of many organisms that has been detected in the airways of patients with CF. This review provides an evidence-based summary of pharmacokinetic/pharmacodynamic (PK/PD), tolerability, and efficacy studies utilizing anti-MRSA antibiotics (ie, ceftaroline, clindamycin, fluoroquinolone derivatives (ciprofloxacin, levofloxacin), glycopeptide derivatives (telavancin, vancomycin), linezolid, rifampin, sulfamethoxazole/trimethoprim (SMZ/TMP), and tetracycline derivatives (doxycycline, minocycline, tigecycline) in the treatment of APE and identifies areas where further study is warranted. A recent utilization study of antimicrobials for anti-MRSA has shown some CF Foundation accredited care centers and affiliate programs are using doses higher than the FDA-approved doses. Further studies are needed to determine the PK/PD properties in CF patients with clindamycin, minocycline, rifampin, SMZ/TMP, telavancin, and tigecycline; as well as, efficacy and tolerability studies with ciprofloxacin, clindamycin, doxycycline, levofloxacin, minocycline, rifampin, SMZ/TMP, in CF patients with MRSA.

The Potential for Treatment Shortening With Higher Rifampicin Doses: Relating Drug Exposure to Treatment Response in Patients With Pulmonary Tuberculosis

Background

Tuberculosis remains a huge public health problem and the prolonged treatment duration obstructs effective tuberculosis control. Higher rifampicin doses have been associated with better bactericidal activity, but optimal dosing is uncertain. This analysis aimed to characterize the relationship between rifampicin plasma exposure and treatment response over 6 months in a recent study investigating the potential for treatment shortening with high-dose rifampicin.

Methods

Data were analyzed from 336 patients with pulmonary tuberculosis (97 with pharmacokinetic data) treated with rifampicin doses of 10, 20, or 35 mg/kg. The response measure was time to stable sputum culture conversion (TSCC). We derived individual exposure metrics with a previously developed population pharmacokinetic model of rifampicin. TSCC was modeled using a parametric time-to-event approach, and a sequential exposure-response analysis was performed.

Results

Higher rifampicin exposures increased the probability of early culture conversion. No maximal limit of the effect was detected within the observed range. The expected proportion of patients with stable culture conversion on liquid medium at week 8 was predicted to increase from 39% (95% confidence interval, 37%-41%) to 55% (49%-61%), with the rifampicin area under the curve increasing from 20 to 175 mg/L·h (representative for 10 and 35 mg/kg, respectively). Other predictors of TSCC were baseline bacterial load, proportion of culture results unavailable, and substitution of ethambutol for either moxifloxacin or SQ109.

Conclusions

Increasing rifampicin exposure shortened TSCC, and the effect did not plateau, indicating that doses >35 mg/kg could be yet more effective. Optimizing rifampicin dosage while preventing toxicity is a clinical priority.

Scaffold Morphing To Identify Novel DprE1 Inhibitors with Antimycobacterial Activity

We report a novel benzimidazole (BI) based DprE1 inhibitor that resulted from scaffold morphing of a 1,4-azaindole series. The clinical progression of the 1,4-azaindole series from our previous work validates the potential of exploring newer chemical entities with antimycobacterial activity driven via a noncovalent inhibition of the decaprenylphosphoryl-β-d-ribose-2'-epimerase (DprE1). The representative compounds from the new scaffold reported in this study exhibited an improved solubility and higher free plasma fraction, while retaining potent DprE1 inhibition and antimycobacterial activity. A representative compound from the benzimidazole series demonstrated good efficacy in a murine model of tuberculosis. Furthermore, molecular modeling of the BI scaffold suggests plausible modes of binding in the active site of DprE1 enzyme from Mycobacterium tuberculosis that can be used for further exploration of the series.

Pharmacokinetics of rifampicin in adult TB patients and healthy volunteers: a systematic review and meta-analysis

Objectives

The objectives of this study were to explore inter-study heterogeneity in the pharmacokinetics (PK) of orally administered rifampicin, to derive summary estimates of rifampicin PK parameters at standard dosages and to compare these with summary estimates for higher dosages.

Methods

A systematic search was performed for studies of rifampicin PK published in the English language up to May 2017. Data describing the C_max and AUC were extracted. Meta-analysis provided summary estimates for PK parameter estimates at standard rifampicin dosages. Heterogeneity was assessed by estimation of the I² statistic and visual inspection of forest plots. Summary AUC estimates at standard and higher dosages were compared graphically and contextualized using preclinical pharmacodynamic (PD) data.

Results

Substantial heterogeneity in PK parameters was evident and upheld in meta-regression. Treatment duration had a significant impact on the summary estimates for rifampicin PK parameters, with C_max 8.98 mg/L (SEM 2.19) after a single dose and 5.79 mg/L (SEM 2.14) at steady-state dosing, and AUC 72.56 mg·h/L (SEM 2.60) and 38.73 mg·h/L (SEM 4.33) after single and steady-state dosing, respectively. Rifampicin dosages of at least 25 mg/kg are required to achieve plasma PK/PD targets defined in preclinical studies.

Conclusions

Vast inter-study heterogeneity exists in rifampicin PK parameter estimates. This is not explained by the available modifying variables. The recommended dosage of rifampicin should be increased to improve efficacy. This study provides an important point of reference for understanding rifampicin PK at standard dosages as efforts to explore higher dosing strategies continue in this field.

Protocol for the management of newly diagnosed cases of tuberculosis

To achieve the targets and milestones set by the World Health Organization (3) to their 'End TB Strategy' to stop the global TB epidemic by 2035 and India's commitment to eliminate this disease from the country by 2025 (4), it will be important to improve the case finding and effectively treat cases of tuberculosis both in the public and the private sector, the latter still holding a major share. To strengthen the management of tuberculosis in the private sector and to have uniformity in the treatment, we need to have a protocol, suitable to our socio-economic conditions, which will not only provide guidance in getting better treatment outcomes, but also help to interrupt transmission of the disease in the community, besides curbing the development of drug resistance. Several guidelines on the management of tuberculosis are available, but these are considered as very good starting points for treatment but not the only treatment option, since guidelines cannot address every possible situation and substitute for good clinical judgment (5).Hence to meet these requirements and shortcomings following protocol is provided to manage cases of tuberculosis and resolve several issues related to it.

Optimization of a paediatric fixed dose combination mini-tablet and dosing regimen for the first line treatment of tuberculosis

We aim to optimize the paediatric dosing regimen of isoniazid, rifampicin and pyrazinamide for the first-line treatment of tuberculosis, based on a fixed dose combination (FDC) mini-tablet using simulations. An optimization problem was set up to determine the 3 strengths of the drugs of the mini-tablet and 4 cutoff points that define the weight bands of a dosing chart, simultaneously. Using Monte Carlo simulations, first, exposure targets were determined for the 3 drugs, from published population pharmacokinetic models for adults, assuming that the approved doses for adults are de facto efficacious. Then optimal strengths and cutoff points were determined by matching children exposures generated from population pharmacokinetic models to the adults targets. The optimal dosing strengths of the FDC tablet were found to be 95 mg of rifampicin, 200 mg of pyrazinamide and 75 mg of isoniazid, and the 4 body weight bands for 1 to 4 mini-tablets, respectively were: 4 to 8 kg, 8 to 12 kg, 12 to 18 kg and 18 to 28 kg. Children with body weight ≥ 28 kg will be treated with adult dosages. The higher doses proposed were evaluated to be much closer to the adult targets compared to the existing recommended by WHO paediatric doses.

Distribution of plasma concentrations of first-line anti-TB drugs and individual MICs: a prospective cohort study in a low endemic setting

Background

Therapeutic drug monitoring (TDM) could improve current TB treatment, but few studies have reported pharmacokinetic data together with MICs.

Objectives

To investigate plasma concentrations of rifampicin, isoniazid, pyrazinamide and ethambutol along with MICs.

Methods

Drug concentrations of rifampicin, isoniazid, pyrazinamide and ethambutol were analysed pre-dose and 2, 4 and 6 h after drug intake at week 2 in 31 TB patients and MICs in BACTEC 960 MGIT were determined at baseline. The highest plasma concentrations at 2, 4 and 6 h post-dose (Chigh) were determined, as well as estimates of Chigh/MIC and area under the concentration-time curve (AUC0-6)/MIC including the corresponding ratios based on calculated free-drug concentrations. This trial was registered at www.clinicaltrials.gov (NCT02042261).

Results

After 2 weeks of treatment, the median Chigh values for rifampicin, isoniazid, pyrazinamide and ethambutol were 10.0, 5.3, 41.1 and 3.3 mg/L respectively. Lower than recommended drug concentrations were detected in 42% of the patients for rifampicin (<8 mg/L), 19% for isoniazid (<3 mg/L), 27% for pyrazinamide (<35 mg/L) and 16% for ethambutol (<2 mg/L). The median Chigh/MIC values for rifampicin, isoniazid, pyrazinamide and ethambutol were 164, 128, 1.3 and 2.5, respectively, whereas the AUC0-6/MIC was 636 (range 156-2759) for rifampicin and 351 (range 72-895) for isoniazid.

Conclusions

We report low levels of first-line TB drugs in 16%-42% of patients, in particular for rifampicin. There was a wide distribution of the ratios between drug exposures and MICs. The future use of MIC determinations in TDM is dependent on the development of a reference method and clinically validated pharmacokinetic/pharmacodynamic targets.

Efficacy and Safety of High-Dose Rifampin in Pulmonary Tuberculosis. A Randomized Controlled Trial

RATIONALE

We examined whether increased rifampin doses could shorten standard therapy for tuberculosis without increased toxicity.

OBJECTIVES

To assess the differences across three daily oral doses of rifampin in change in elimination rate of Mycobacterium tuberculosis in sputum and frequency of rifampin-related adverse events.

METHODS

We conducted a blinded, randomized, controlled phase 2 clinical trial of 180 adults with new smear-positive pulmonary tuberculosis, susceptible to isoniazid and rifampin. We randomized 1:1:1 to rifampin at 10, 15, and 20 mg/kg/d during the intensive phase. We report the primary efficacy and safety endpoints: change in elimination rate of M. tuberculosis log₁₀ colony-forming units and frequency of grade 2 or higher rifampin-related adverse events. We report efficacy by treatment arm and by primary (area under the plasma concentration-time curve [AUC]/minimum inhibitory concentration [MIC]) and secondary (AUC) pharmacokinetic exposure.

MEASUREMENTS AND MAIN RESULTS

Each 5-mg/kg/d increase in rifampin dose resulted in differences of -0.011 (95% confidence interval, -0.025 to +0.002; P = 0.230) and -0.022 (95% confidence interval, -0.046 to -0.002; P = 0.022) log₁₀ cfu/ml/d in the modified intention-to-treat and per-protocol analyses, respectively. The elimination rate in the per-protocol population increased significantly with rifampin AUC_0-6 (P = 0.011) but not with AUC_0-6/MIC_99.9 (P = 0.053). Grade 2 or higher rifampin-related adverse events occurred with similar frequency across the three treatment arms: 26, 31, and 23 participants (43.3%, 51.7%, and 38.3%, respectively) had at least one event (P = 0.7092) up to 4 weeks after the intensive phase. Treatment failed or disease recurred in 11 participants (6.1%).

CONCLUSIONS

Our findings of more rapid sputum sterilization and similar toxicity with higher rifampin doses support investigation of increased rifampin doses to shorten tuberculosis treatment. Clinical trial registered with www.clinicaltrials.gov (NCT 01408914) .

Evolution of rifampicin treatment for tuberculosis

Rifampicin was discovered in 1965 and remains one of the most important drugs in tuberculosis treatment that is valued for its sterilizing activity and ability to shorten treatment. Antimicrobial activity of rifampicin was initially proved in vitro; subsequently numerous in vivo studies showed the bactericidal properties and dose-dependent effect of rifampicin. Rifampicin was first during the late 1960s to treat patients suffering from chronic drug-resistant pulmonary TB. Decades later, rifampicin continues to be studied with particular emphasis on whether higher doses could shorten the duration of treatment without increasing relapse or having adverse effects. Lesion-specific drug penetration and pharmacokinetics of rifampicin are improving our understanding of effective concentration while potentially refining drug regimen designs. Another prospective aspect of high-dose rifampicin is its potential use in treating discrepant mutation thereby eliminating the need for MDR treatment. To date, several clinical trials have shown the safety, efficacy, and tolerability of high-dose rifampicin. Currently, high-dose rifampicin has been used successfully in a routine clinical setting for the treatment of high-risk patients. However, the WHO and other relevant policy makers have not committed to implementing a controlled rollout thereof. This review describes the course that rifampicin has travelled to the present-day exploration of high-dose rifampicin treatment.

Intracellular PD Modelling (PDi) for the Prediction of Clinical Activity of Increased Rifampicin Dosing

Increasing rifampicin (RIF) dosages could significantly reduce tuberculosis (TB) treatment durations. Understanding the pharmacokinetic-pharmacodynamics (PK-PD) of increasing RIF dosages could inform clinical regimen selection. We used intracellular PD modelling (PD_i) to predict clinical outcomes, primarily time to culture conversion, of increasing RIF dosages. PD_i modelling utilizes in vitro-derived measurements of intracellular (macrophage) and extracellular Mycobacterium tuberculosis sterilization rates to predict the clinical outcomes of RIF at increasing doses. We evaluated PD_i simulations against recent clinical data from a high dose (35 mg/kg per day) RIF phase II clinical trial. PD_i-based simulations closely predicted the observed time-to-patient culture conversion status at eight weeks (hazard ratio: 2.04 (predicted) vs. 2.06 (observed)) for high dose RIF-based treatments. However, PD_i modelling was less predictive of culture conversion status at 26 weeks for high-dosage RIF (99% predicted vs. 81% observed). PD_i-based simulations indicate that increasing RIF beyond 35 mg/kg/day is unlikely to significantly improve culture conversion rates, however, improvements to other clinical outcomes (e.g., relapse rates) cannot be ruled out. This study supports the value of translational PD_i-based modelling in predicting culture conversion rates for antitubercular therapies and highlights the potential value of this platform for the improved design of future clinical trials.

Attainment of target rifampicin concentrations in cerebrospinal fluid during treatment of tuberculous meningitis

Objective:

There is considerable uncertainty regarding the optimal use of rifampicin for the treatment of tuberculous (TB) meningitis. A pharmacokinetic modeling and simulation study of rifampicin concentrations in cerebrospinal fluid (CSF) during TB meningitis treatment was performed in this study.

Methods:

Parameters for rifampicin pharmacokinetics in CSF were estimated using individual-level rifampicin pharmacokinetic data, and the model was externally validated in three separate patient cohorts. Monte Carlo simulations of rifampicin serum and CSF concentrations were performed. The area under the rifampicin CSF concentration-versus-time curve during 24 h (AUC_0–24) relative to the minimum inhibitory concentration (MIC) served as the pharmacodynamic target.

Results:

Across all simulated patients on the first treatment day, 85% attained the target AUC_0–24/MIC ratio of 30 under a weight-based dosing scheme approximating 10 mg/kg. At the rifampicin MIC of 0.5 mg/l, the probability of AUC_0–24/MIC target attainment was 26%. With an intensified dosing strategy corresponding to 20 mg/kg, target attainment increased to 99%, including 93% with a MIC of 0.5 mg/l.

Conclusions:

Under standard dosing guidelines, few TB meningitis patients would be expected to attain therapeutic rifampicin exposures in CSF when the MIC is ≤0.5 mg/l. Either downward adjustment of the rifampicin MIC breakpoint in the context of TB meningitis, or intensified rifampicin dosing upwards of 20 mg/kg/day, would reflect the likelihood of pharmacodynamic target attainment in CSF.

Intensified antibiotic treatment of tuberculosis meningitis

INTRODUCTION

Meningitis is the most severe manifestation of tuberculosis, resulting in death or disability in over 50% of those affected, with even higher morbidity and mortality among patients with HIV or drug resistance. Antimicrobial treatment of Tuberculous meningitis (TBM) is similar to treatment of pulmonary tuberculosis, although some drugs show poor central nervous system penetration. Therefore, intensification of antibiotic treatment may improve TBM treatment outcomes. Areas covered: In this review, we address three main areas: available data for old and new anti-tuberculous agents; intensified treatment in specific patient groups like HIV co-infection, drug-resistance, and children; and optimal research strategies. Expert commentary: There is good evidence from preclinical, clinical, and modeling studies to support the use of high-dose rifampicin in TBM, likely to be at least 30 mg/kg. Higher dose isoniazid could be beneficial, especially in rapid acetylators. The role of other first and second line drugs is unclear, but observational data suggest that linezolid, which has good brain penetration, may be beneficial. We advocate the use of molecular pharmacological approaches, physiologically based pharmacokinetic modeling and pharmacokinetic-pharmacodynamic studies to define optimal regimens to be tested in clinical trials. Exciting data from recent studies hold promise for improved regimens and better clinical outcomes in future.

Forecasting Clinical Dose-Response From Preclinical Studies in Tuberculosis Research: Translational Predictions With Rifampicin

A crucial step for accelerating tuberculosis drug development is bridging the gap between preclinical and clinical trials. In this study, we developed a preclinical model-informed translational approach to predict drug effects across preclinical systems and early clinical trials using the in vitro-based Multistate Tuberculosis Pharmacometric (MTP) model using rifampicin as an example. The MTP model predicted rifampicin biomarker response observed in 1) a hollow-fiber infection model, 2) a murine study to determine pharmacokinetic/pharmacodynamic indices, and 3) several clinical phase IIa early bactericidal activity (EBA) studies. In addition, we predicted rifampicin biomarker response at high doses of up to 50 mg/kg, leading to an increased median EBA0-2 days (90% prediction interval) of 0.513 log CFU/mL/day (0.310; 0.701) compared to the standard dose of 10 mg/kg of 0.181 log/CFU/mL/day (0.076; 0.483). These results suggest that the translational approach could assist in the selection of drugs and doses in early-phase clinical tuberculosis trials.

Pharmacokinetic/Pharmacodynamic Background and Methods and Scientific Evidence Base for Dosing of Second-line Tuberculosis Drugs

A World Health Organization workshop systematically examined the evidence base for dosing second-line tuberculosis drugs, identifying knowledge gaps. To fill these in, pharmacokinetics/pharmacodynamics, Monte Carlo experiments, and artificial intelligence algorithms were used in hollow-fiber model studies and clinical data analyses.

Synergistic Antimicrobial Activity of Colistin in Combination with Rifampin and Azithromycin against Escherichia coli Producing MCR-1

The lack of available antibiotics is a global public health problem due to the emergence of antimicrobial resistance. Effective therapeutic regimens are urgently needed against Escherichia coli strains that produce the colistin resistance gene mcr-1 and to inhibit the emergence of resistance. In this study, we assessed the antimicrobial activity of a series of concentrations of colistin-based combinations with rifampin and/or azithromycin against three strains of Escherichia coli, including colistin-resistant isolate MZ1501^R, isolate HE1704^R that produces MCR-1, and colistin-susceptible isolate MZ1509^S Experiments were conducted with a medium inoculum of ∼10⁷ CFU/ml over 48 h. Subsequently, the in vivo therapeutic effect was investigated using a neutropenic mouse thigh infection model. Almost all monotherapies showed unsatisfactory antibacterial activity against E. coli isolates producing MCR-1. In contrast, colistin in combination with rifampin or azithromycin resulted in an obvious decrease in the bacterial burden albeit with regrowth. More obviously, synergistic antimicrobial activity of colistin-based triple-combination therapy with rifampin and azithromycin was observed, resulting in a rapid and exhaustive antibacterial effect. In vivo treatments confirmed these findings, where mean decreases of 0.38 to 0.90 log₁₀ CFU and 1.27 to 1.78 log₁₀ CFU were noted after 24 h and 48 h of treatment, respectively, against colistin-resistant E. coli strains when 5 mg/kg of body weight of colistin was combined with rifampin and azithromycin. Colistin-based combinations with rifampin and azithromycin provide a more active therapeutic regimen than monotherapy or colistin-based double combinations against E. coli producing MCR-1.

Synthesis, antituberculosis studies and biological evaluation of new quinoline derivatives carrying 1,2,4-oxadiazole moiety

Tuberculosis is the infectious disease caused by mycobacterium tuberculosis (Mtb), responsible for the utmost number of deaths annually across the world. Herein, twenty-one new substituted 1,2,4-oxadiazol-3-ylmethyl-piperazin-1-yl-quinoline derivatives were designed and synthesized through multistep synthesis followed by in vitro evaluation of their antitubercular potential against Mtb WT H37Rv. The compound QD-18 was found to be promising with MIC value of 0.5 µg/ml and QD-19 to QD-21 were also remarkable with MIC value of 0.25 µg/ml. Additionally, we have carried out experiments to confirm the metabolic stability, cytotoxicity and pharmacokinetics of these compounds along with kill kinetics of QD-18. These compounds were found to be orally bioavailable and highly effective. Altogether, these results indicate that QD-18, QD-19, QD-20 and QD-21 are promising lead compounds for the development of a novel chemical class of antitubercular drugs.

Exploring Peyer's Patch Uptake as a Strategy for Targeted Lung Delivery of Polymeric Rifampicin Nanoparticles

Uptake of nanoparticles through Peyer's Patches following oral administration could enable translocation through lymph to lymphatic organs like the lungs. An important consideration, however, is nanosize and particle hydrophobicity. Furthermore, as delivering the nanoparticles to the intestine where the Peyer's Patches are localized is important, their intact and rapid transit through the stomach into the intestine is highly desirable. We report hydrophobization of mucoadhesive Rifampicin-GantrezAN-119 nanoparticles (GzNP) using a hydrophobic polymer, ethyl cellulose (EC), with the objectives of augmenting Peyer's Patch uptake due to enhanced hydrophobicity and increased intestinal localization as a result of decreased mucoadhesion. RIF-Gantrez-EC nanoparticles (ECGzNP2) exhibited >13% RIF loading and an average particle size of 400-450 nm, which is appropriate for translation through lymph following Peyer's Patch uptake. Higher contact angle (67.3 ± 3.5° vs 30.3 ± 2.1°) and lower mucoadhesion (30.7 ± 4.8 g vs 87.0 ± 3.0 g) of ECGzNP2 over GzNP confirmed hydrophobization and lower mucoadhesion. Fluorescence photomicrographs of intraduodenally administered coumarin-labeled RIF-NP in rats demonstrated higher Peyer's Patch uptake with ECGzNP2, while the increased lung/plasma RIF ratio signified lymph mediated lung targeting. The gastrointestinal transit study in rats, which revealed a significantly higher intestine-to-stomach accumulation ratio with ECGzNP2 (3.4) compared to GzNP (1.0) [ p < 0.05], confirmed availability of the NP in the intestine for Peyer's Patch uptake. Such uptake enabled 182.4 ± 22.6% increase in relative bioavailability, a ∼2-fold higher plasma AUC/MIC ratio and significantly higher lung concentration with ECGzNP2, thereby proposing better efficacy. A significantly higher lung/liver ratio with ECGzNP2 also suggested lower hepatic exposure. The repeated dose 28-day oral toxicity study demonstrated the safety of the nanocarrier and reduced hepatotoxicity with ECGzNP2 compared to RIF. We hereby demonstrate uptake of orally administered NP through Peyer's Patches as a feasible strategy for lung targeting.

Efficacy of Colistin and Its Combination With Rifampin in Vitro and in Experimental Models of Infection Caused by Carbapenemase-Producing Clinical Isolates of Klebsiella pneumoniae

Despite the relevance of carbapenemase-producing Klebsiella pneumoniae (CP-Kp) infections there are a scarce number of studies to evaluate in vivo the efficacy of combinations therapies. The bactericidal activity of colistin, rifampin, and its combination was studied (time–kill curves) against four clonally unrelated clinical isolates of CP-Kp, producing VIM-1, VIM-1 plus DHA-1(acquired AmpC β-lactamase), OXA-48 plus CTX-M-15 (extended spectrum β-lactamase) and KPC-3, respectively, with colistin MICs of 0.5, 64, 0.5, and 32 mg/L, respectively. The efficacies of antimicrobials in monotherapy and in combination were tested in a murine peritoneal sepsis model, against all the CP-Kp. Their efficacies were tested in the pneumonia model against the OXA-48 plus CTX-M-15 producers. The development of colistin-resistance was analyzed for the colistin-susceptible strains in vitro and in vivo. In vitro, colistin plus rifampin was synergistic against all the strains at 24 h. In vivo, compared to the controls, rifampin alone reduced tissue bacterial concentrations against VIM-1 and OXA-48 plus CTX-M-15 strains; CMS plus rifampin reduced tissue bacterial concentrations of these two CP-Kp and of the KPC-3 strain. Rifampin and the combination increased the survival against the KPC-3 strain; in the pneumonia model, the combination also improved the survival. No resistant mutants appeared with the combination. In conclusion, CMS plus rifampin had a low and heterogeneous efficacy in the treatment of severe peritoneal sepsis model due to CP-Kp producing different carbapenemases, increasing survival only against the KPC-3 strain. The combination showed efficacy in the less severe pneumonia model. The combination prevented in vitro and in vivo the development of colistin resistant mutants.

Emergence and selection of isoniazid and rifampin resistance in tuberculosis granulomas

Drug resistant tuberculosis is increasing world-wide. Resistance against isoniazid (INH), rifampicin (RIF), or both (multi-drug resistant TB, MDR-TB) is of particular concern, since INH and RIF form part of the standard regimen for TB disease. While it is known that suboptimal treatment can lead to resistance, it remains unclear how host immune responses and antibiotic dynamics within granulomas (sites of infection) affect emergence and selection of drug-resistant bacteria. We take a systems pharmacology approach to explore resistance dynamics within granulomas. We integrate spatio-temporal host immunity, INH and RIF dynamics, and bacterial dynamics (including fitness costs and compensatory mutations) in a computational framework. We simulate resistance emergence in the absence of treatment, as well as resistance selection during INH and/or RIF treatment. There are four main findings. First, in the absence of treatment, the percentage of granulomas containing resistant bacteria mirrors the non-monotonic bacterial dynamics within granulomas. Second, drug-resistant bacteria are less frequently found in non-replicating states in caseum, compared to drug-sensitive bacteria. Third, due to a steeper dose response curve and faster plasma clearance of INH compared to RIF, INH-resistant bacteria have a stronger influence on treatment outcomes than RIF-resistant bacteria. Finally, under combination therapy with INH and RIF, few MDR bacteria are able to significantly affect treatment outcomes. Overall, our approach allows drug-specific prediction of drug resistance emergence and selection in the complex granuloma context. Since our predictions are based on pre-clinical data, our approach can be implemented relatively early in the treatment development process, thereby enabling pro-active rather than reactive responses to emerging drug resistance for new drugs. Furthermore, this quantitative and drug-specific approach can help identify drug-specific properties that influence resistance and use this information to design treatment regimens that minimize resistance selection and expand the useful life-span of new antibiotics.

Suboptimal Antituberculosis Drug Concentrations and Outcomes in Small and HIV-Coinfected Children in India: Recommendations for Dose Modifications

This work aimed to evaluate the once‐daily antituberculosis treatment as recommended by the new Indian pediatric guidelines. Isoniazid, rifampin, and pyrazinamide concentration–time profiles and treatment outcome were obtained from 161 Indian children with drug‐sensitive tuberculosis undergoing thrice‐weekly dosing as per previous Indian pediatric guidelines. The exposure–response relationships were established using a population pharmacokinetic‐pharmacodynamic approach. Rifampin exposure was identified as the unique predictor of treatment outcome. Consequently, children with low body weight (4–7 kg) and/or HIV infection, who displayed the lowest rifampin exposure, were associated with the highest probability of unfavorable treatment (therapy failure, death) outcome (P_unfavorable). Model‐based simulation of optimized (P_unfavorable ≤ 5%) rifampin once‐daily doses were suggested per treatment weight band and HIV coinfection status (33% and 190% dose increase, respectively, from the new Indian guidelines). The established dose‐exposure–response relationship could be pivotal in the development of future pediatric tuberculosis treatment guidelines.

Evaluation of the Adequacy of the 2010 Revised World Health Organization Recommended Dosages of the First-line Antituberculosis Drugs for Children: Adequacy of Revised Dosages of TB Drugs for Children

BACKGROUND

The World Health Organization recommended increased dosages of the first-line antituberculosis (anti-TB) drugs for children in 2010. We examined the frequency of and factors associated with low plasma maximum concentration (Cmax) of each drug in children treated with the revised dosages.

METHODS

Children on anti-TB therapy for at least 4 weeks underwent pharmacokinetic testing. Plasma Cmax below the lower limit of proposed reference range was considered low. Bivariate and multivariate analyses were used to examine the factors associated with low Cmax of each drug.

RESULTS

Of the 100 children, 58% were male, 50% HIV-infected and 49% younger than 5 years old. The median (interquartile range) Cmax was 5.9 (4.5-7.7) µg/mL for isoniazid, 6.5 (4.9-8.8) µg/mL for rifampin, 26.0 (21.2-33.4) µg/mL for pyrazinamide and 1.7 (0.9-2.7) µg/mL for ethambutol. There was a strong correlation between Cmax and AUC0-8h for all drugs. Low Cmax occurred in 9/100 (9.0%), 61/100 (61.0%), 17/97 (17.5%) and 60/97 (61.9%) for isoniazid, rifampin, pyrazinamide and ethambutol, respectively. In addition, 75/97 (77.3%) children had pyrazinamide Cmax < 35 µg/mL. Factors associated with low Cmax were NAT2 metabolizer phenotype status for isoniazid; height, dosage and HIV coinfection status for rifampin; height for pyrazinamide; and age, dosage and HIV coinfection status for ethambutol.

CONCLUSIONS

The high frequency of low rifampin and ethambutol Cmax in our study is consistent with emerging pharmacokinetic data in children treated according to the new WHO recommendations. Higher dosages than currently recommended especially for rifampin may be necessary in children.

Assessing the Combined Antibacterial Effect of Isoniazid and Rifampin on Four Mycobacterium tuberculosis Strains Using In Vitro Experiments and Response-Surface Modeling

While isoniazid and rifampin have been the cornerstone of tuberculosis therapy caused by drug-susceptible Mycobacterium tuberculosis for more than 40 years, their combined action has never been thoroughly assessed by modern quantitative pharmacology approaches. The aims of this work were to perform in vitro experiments and mathematical modeling of the antibacterial effect of isoniazid and rifampin alone and in combination against various strains of Mycobacterium tuberculosis After MIC determination of H37Rv and three strains belonging to the Beijing, Euro-American, and Indo-Oceanic lineages, the antibacterial effects of isoniazid and rifampin alone and in combination were studied in static time-kill experiments. A sigmoidal maximum effect model (Hill equation) and a response-surface model were used to describe the effect of the drugs alone and in combination, respectively. The killing effect of isoniazid and rifampin alone were well described by the Hill equation. Rifampin displayed a more concentration-dependent effect than isoniazid around the MIC. The pharmacodynamics parameters of each drug (maximal effect, median effect concentration, and coefficient of sigmoidicity) were quite similar between the four strains. The response-surface model from Minto et al. fit data of combined effect very well with low bias and imprecision (C. F. Minto, T. W. Schnider, T. G. Short, K. M. Gregg, A. Gentilini, Anesthesiology 92:1603-1616, 2000, https://doi.org/10.1097/00000542-200006000-00017). Response-surface modeling showed that the combined action of isoniazid and rifampin was synergistic for the H37Rv, Beijing, and Euro-American strains but only additive for the Indo-Oceanic strain. This study can serve as a motivating example for preclinical evaluation of combined action of antituberculous drugs.

Pharmacokinetics and pharmacogenetics of anti-tubercular drugs: a tool for treatment optimization?

INTRODUCTION

WHO global strategy is to end tuberculosis epidemic by 2035. Pharmacokinetic and pharmacogenetic studies are increasingly performed and might confirm their potential role in optimizing treatment outcome in specific settings and populations. Insufficient drug exposure seems to be a relevant factor in tuberculosis outcome and for the risk of phenotypic resistance. Areas covered: This review discusses available pharmacokinetic and pharmacogenetic data of first and second-line antitubercular agents in relation to efficacy and toxicity. Pharmacodynamic implications of optimized drugs and new options regimens are reviewed. Moreover a specific session describes innovative investigations on drug penetration. Expert opinion: The optimal use of available antitubercular drugs is paramount for tuberculosis control and eradication. Whilst trials are still on-going, higher rifampicin doses should be reserved to treatment for tubercular meningitis. Therapeutic Drug Monitoring with limiting sampling strategies is advised in patients at risk of failure or with slow treatment response. Further studies are needed in order to provide definitive recommendations of pharmacogenetic-based individualization: however lower isoniazid doses in NAT2 slow acetylators and higher rifampicin doses in individuals with SLCO1B1 loss of function genes are promising strategies. Finally in order to inform tailored strategies we need more data on tissue drug penetration and pharmacological modelling.

Screening of antitubercular compound library identifies novel ATP synthase inhibitors of Mycobacterium tuberculosis

A limited number of anti-tuberculosis drug candidates with novel mode of action have entered clinical trials in recent years. ATP synthase is one such validated drug target which has yielded a drug recently. The aim of this study was to identify the novel chemical scaffolds targeting the Mycobacterium tuberculosis (M. tuberculosis) ATP synthase. In this study, inverted membrane vesicles of Mycobacterium smegmatis were prepared to establish luciferin based ATP estimation assay. This assay was used to screen 700 compounds which were earlier found to be active on the whole cell of M. tuberculosis. Antibacterial activity of hits against various susceptible and drug-resistant strains of M. tuberculosis was evaluated using the microplate alamar blue assay and their cytotoxicity was also determined to select the safe compounds for further study. Screening of 700 compounds resulted in the identification of two compounds (5228485 and 5220632) exhibiting an IC₅₀ of 0.32 and 4.0 μg/ml respectively. Both compounds showed excellent anti-TB activity (MIC of 0.5-2.0 μg/ml against Mtb H₃₇Rv) and low cytotoxicity in human cell line and sub-mitochondrial particles. The three-dimensional structure of M. tuberculosis ATPase was predicted using in-silico approach and docking studies were performed with the active compounds. The interaction between compounds and bacterial ATP synthase was confirmed by molecular docking analysis. In conclusion screening of compound library has resulted in the identification of two novel chemical scaffolds targeting mycobacterial ATP synthase.

Pharmacokinetics, Tolerability, and Bacteriological Response of Rifampin Administered at 600, 900, and 1,200 Milligrams Daily in Patients with Pulmonary Tuberculosis

In a multiple-dose-ranging trial, we previously evaluated higher doses of rifampin in patients for 2 weeks. The objectives of the current study were to administer higher doses of rifampin for a longer period to compare the pharmacokinetics, safety/tolerability, and bacteriological activity of such regimens. In a double-blind, randomized, placebo-controlled, phase II clinical trial, 150 Tanzanian patients with tuberculosis (TB) were randomized to receive either 600 mg (approximately 10 mg/kg of body weight), 900 mg, or 1,200 mg rifampin combined with standard doses of isoniazid, pyrazinamide, and ethambutol administered daily for 2 months. Intensive pharmacokinetic sampling occurred in 63 patients after 6 weeks of treatment, and safety/tolerability was assessed. The bacteriological response was assessed by culture conversion in liquid and solid media. Geometric mean total exposures (area under the concentration-versus-time curve up to 24 h after the dose) were 24.6, 50.8, and 76.1 mg · h/liter in the 600-mg, 900-mg, and 1,200-mg groups, respectively, reflecting a nonlinear increase in exposure with the dose (P < 0.001). Grade 3 adverse events occurred in only 2 patients in the 600-mg arm, 4 patients in the 900-mg arm, and 5 patients in the 1,200-mg arm. No significant differences in the bacteriological response were observed. Higher daily doses of rifampin (900 and 1,200 mg) resulted in a more than proportional increase in rifampin exposure in plasma and were safe and well tolerated when combined with other first-line anti-TB drugs for 2 months, but they did not result in improved bacteriological responses in patients with pulmonary TB. These findings have warranted evaluation of even higher doses of rifampin in follow-up trials. (This study has been registered at ClinicalTrials.gov under identifier NCT00760149.).

Clinical and pharmacological hallmarks of rifapentine's use in diabetes patients with active and latent tuberculosis: do we know enough?

Rifapentine is a rifamycin derivate approved by the US Food and Drug Administration in 1998 for the treatment of active, drug-susceptible tuberculosis (TB). In 2014, rifapentine was approved for the treatment of latent TB infection in patients at high risk of progression to active disease and is currently under evaluation by the European Medicines Agency. Expanding indications of rifapentine largely affect diabetes patients, since about one-third of them harbor latent TB. Clinical consequences of rifapentine use in this population and potentially harmful interactions with hypoglycemic agents are widely underexplored and generally considered similar to the ones of rifampicin. Indeed, rifapentine too may decrease blood levels of many oral antidiabetics and compete with them for protein-binding sites and/or transporters. However, the two drugs differ in protein-binding degree, the magnitude of cytochrome P450 induction and auto-induction, the degree of renal elimination, and so on. Rifapentine seems to be more suitable for use in diabetes patients with renal impairment, owing to the fact that it does not cause renal toxicity, and it is eliminated via kidneys in smaller proportions than rifampicin. On the other hand, there are no data related to rifapentine use in patients >65 years, and hypoalbuminemia associated with diabetic kidney disease may affect a free fraction of rifapentine to a greater extent than that of rifampicin. Until more pharmacokinetic information and information on the safety of rifapentine use in diabetic patients and drug–drug interactions are available, diabetes in TB patients treated with rifapentine should be managed with insulin analogs, and glucose and rifapentine plasma levels should be closely monitored.

Preclinical Efficacy Testing of New Drug Candidates

This is a review of the preclinical efficacy testing of new antituberculosis drug candidates. It describes existing dynamic in vitro and in vivo models of antituberculosis chemotherapy and their utility in preclinical evaluations of promising new drugs and combination regimens, with an effort to highlight recent developments. Emphasis is given to the integration of quantitative pharmacokinetic/pharmacodynamic analyses and the impact of lesion pathology on drug efficacy. Discussion also includes in vivo models of chemotherapy of latent tuberculosis infection.

A Population Pharmacokinetic Model Incorporating Saturable Pharmacokinetics and Autoinduction for High Rifampicin Doses

Accumulating evidence suggests that increasing doses of rifampicin may shorten tuberculosis treatment. The PanACEA HIGHRIF1 trial assessed safety, pharmacokinetics, and antimycobacterial activity of rifampicin at doses up to 40 mg/kg. Eighty-three pulmonary tuberculosis patients received 10, 20, 25, 30, 35, or 40 mg/kg rifampicin daily over 2 weeks, supplemented with standard doses of isoniazid, pyrazinamide, and ethambutol in the second week. This study aimed at characterizing rifampicin pharmacokinetics observed in HIGHRIF1 using nonlinear mixed effects modeling. The final population pharmacokinetic model included an enzyme turnover model accounting for time-dependent elimination due to autoinduction, concentration-dependent clearance, and dose-dependent bioavailability. The relationship between clearance and concentration was characterized by a Michaelis-Menten relationship. The relationship between bioavailability and dose was described using an E_max relationship. The model will be key in determining exposure-response relationships for rifampicin and should be considered when designing future trials and when treating future patients with high-dose rifampicin.

Determination of protein-unbound, active rifampicin in serum by ultrafiltration and Ultra Performance Liquid Chromatography with UV detection. A method suitable for standard and high doses of rifampicin

Rifampicin is the most important antibiotic in use for the treatment of tuberculosis (TB). Preclinical and clinical data suggest that higher doses of rifampicin, resulting in disproportionally higher systemic exposures to the drug, are more effective. Serum concentrations of rifampicin are the intermediary link between the dose administered and eventual response and only protein-unbound (free) rifampicin is pharmacologically active. The objective of this work was to develop an ultra performance liquid chromatography assay for protein-unbound rifampicin in serum with ultrafiltration, carried out at a sample temperature of 37°C, suitable for measurement of concentrations achieved after currently used and higher doses of rifampicin. Human serum was equilibrated at 37°C and ultrafiltrated at the same temperature in a Centrifree YM-30 ultrafiltration device, followed by dilution of the ultrafiltrate with methanol and ascorbic acid. Unbound rifampicin was analyzed using ultra performance liquid chromatography with a BEH C18 column, isocratic elution and ultra-violet (UV) detection. The run time was 5min. The assay was linear over the concentration range of 0.065-26mg/L rifampicin in ultrafiltrate. Accuracies for measurement of rifampicin in ultrafiltrate were 97% and 102% at the higher and lower limits of quantitation. Accuracy of the ultrafiltration process cannot be established, as it is not possible to spike blank serum with known amounts of protein-unbound rifampicin. Within- and between-day precision of the method including ultrafiltration as well as after ultrafiltration were within prespecified limits (CV<10%). Dilution of the ultrafiltrate with methanol and ascorbic acid kept rifampicin in solution and prevented it from degradation. Rifampicin loss during the ultrafiltration process and variation in analytical results when using two different batches of ultrafiltration devices were both limited. Processed ultrafiltrate samples were stable for 3days in the autosampler. The developed method can be applied in pharmacokinetic research, studying exposure-response relationships for rifampicin when administered at higher than currently used doses.

Pharmacokinetic Evidence from the HIRIF Trial To Support Increased Doses of Rifampin for Tuberculosis

Rifamycins exhibit concentration-dependent killing of Mycobacterium tuberculosis; higher exposures potentially induce better outcomes. We randomized 180 tuberculosis patients in Peru to receive rifampin at 10, 15, or 20 mg/kg/day. A total of 168 had noncompartmental pharmacokinetic analyses; 67% were sampled twice, and 33% were sampled six times. The doses administered were well tolerated. The median area under the concentration-time curve from 0 to 6 h (interquartile range) was 24.9 (17.6 to 32.1), 43.1 (30.3 to 57.5), or 55.5 (35.7 to 73.2) h · μg/ml. The median maximum drug concentration in serum in the experimental arms reached the target of 8 μg/ml. Continued investigation of higher rifampin doses is warranted. (This study has been registered at ClinicalTrials.gov under registration no. NCT01408914.).

The importance of clinical pharmacokinetic-pharmacodynamic studies in unraveling the determinants of early and late tuberculosis outcomes

Tuberculosis remains a major infectious cause of morbidity and mortality worldwide. Current antibiotic regimens, constructed prior to the development of modern pharmacokinetic-pharmacodynamic (PK–PD) tools, are based on incomplete understanding of exposure–response relationships in drug susceptible and multidrug resistant tuberculosis. Preclinical and population PK data suggest that clinical PK–PD studies may enable therapeutic drug monitoring for some agents and revised dosing for others. Future clinical PK–PD challenges include: incorporation of PK methods to assay free concentrations for all active metabolites; selection of appropriate early outcome measures which reflect therapeutic response; elucidation of genetic contributors to interindividual PK variability; conduct of targeted studies on special populations (including children); and measurement of PK–PD parameters at the site of disease.

Role of vitamin D pathway gene polymorphisms on rifampicin plasma and intracellular pharmacokinetics

AIM

We retrospectively evaluate the pharmacogenetic role of single nucleotide polymorphisms involved in rifampicin transport (SLCO1B1, MDR1 and PXR genes) and vitamin D (VDR, CYP24A1 and CYP27B1 genes) metabolism and activity on drug plasma and intracellular concentrations.

PATIENTS & METHODS

Rifampicin C_max and C_trough were measured at weeks 2 and 4 using Ultra-Performance Liquid Chromatography-tandem mass spectroscopy methods. Allelic discrimination was performed by real-time polymerase chain reaction.

RESULTS

Twenty-four patients were enrolled. At week 2, OATP1B1 521TT and CYP27B1 +2838CC/CT considering plasma and BsmIAA for intraperipheral blood mononuclear cells C_max, remained in regression analysis. Concerning week 4, TaqITC/CC and CYP24A1 22776CT/TT were retained in plasma C_max regression model.

CONCLUSION

This study confirms the role of SLCO1B1 and it suggests the involvement of vitamin D pathway gene polymorphisms in rifampicin pharmacokinetics.

New Paradigm for Translational Modeling to Predict Long-term Tuberculosis Treatment Response

Disappointing results of recent tuberculosis chemotherapy trials suggest that knowledge gained from preclinical investigations was not utilized to maximal effect. A mouse‐to‐human translational pharmacokinetics (PKs) – pharmacodynamics (PDs) model built on a rich mouse database may improve clinical trial outcome predictions. The model included Mycobacterium tuberculosis growth function in mice, adaptive immune response effect on bacterial growth, relationships among moxifloxacin, rifapentine, and rifampin concentrations accelerating bacterial death, clinical PK data, species‐specific protein binding, drug‐drug interactions, and patient‐specific pathology. Simulations of recent trials testing 4‐month regimens predicted 65% (95% confidence interval [CI], 55–74) relapse‐free patients vs. 80% observed in the REMox‐TB trial, and 79% (95% CI, 72–87) vs. 82% observed in the Rifaquin trial. Simulation of 6‐month regimens predicted 97% (95% CI, 93–99) vs. 92% and 95% observed in 2RHZE/4RH control arms, and 100% predicted and observed in the 35 mg/kg rifampin arm of PanACEA MAMS. These results suggest that the model can inform regimen optimization and predict outcomes of ongoing trials.

Critical Review: What Dose of Rifabutin Is Recommended With Antiretroviral Therapy?

Since the advent of combination antiretroviral therapy to successfully treat HIV infection, drug-drug interactions (DDIs) have become a significant problem as many antiretrovirals (ARVs) are metabolized in the liver. Antituberculous therapy traditionally includes rifamycins, particularly rifampicin. Rifabutin (RBT) has shown similar efficacy as rifampicin but induces CYP3A4 to a lesser degree and is less likely to have DDIs with ARVs. We identified 14 DDI pharmacokinetic studies on HIV monoinfected and HIV-tuberculosis coinfected individuals, and the remaining studies were healthy volunteer studies. Although RBT may be coadministered with most nonnucleoside reverse transcriptase inhibitors, identifying the optimal dose with ritonavir-boosted or cobicistat-boosted protease inhibitors is challenging because of concern about adverse effects with increased RBT exposure. Limited healthy volunteer studies on other ARV drug classes and RBT suggest that dose modification may be unnecessary. The paucity of data assessing clinical tuberculosis endpoints concurrently with RBT and ARV pharmacokinetics limits evidence-based recommendations on the optimal dose of RBT within available ARV drug classes.