Sterilizing Effect of Ertapenem-Clavulanate in a Hollow-Fiber Model of Tuberculosis and Implications on Clinical Dosing

Dynamic In Vitro PK/PD Infection Models for the Development and Optimisation of Antimicrobial Regimens: A Narrative Review

The antimicrobial concentration-time profile in humans affects antimicrobial activity, and as such, it is critical for preclinical infection models to simulate human-like dynamic concentration-time profiles for maximal translatability. This review discusses the setup, principle, and application of various dynamic in vitro PK/PD infection models commonly used in the development and optimisation of antimicrobial treatment regimens. It covers the commonly used dynamic in vitro infection models, including the one-compartment model, hollow fibre infection model, biofilm model, bladder infection model, and aspergillus infection model. It summarises the mathematical methods for the simulation of the pharmacokinetic profile of single or multiple antimicrobials when using the serial or parallel configurations of in vitro systems. Dynamic in vitro models offer reliable pharmacokinetic/pharmacodynamic data to help define the initial dosing regimens of new antimicrobials that can be developed further in clinical trials. They can also help in the optimisation of dosing regimens for existing antimicrobials, especially in the presence of emerging antimicrobial resistance. In conclusion, dynamic in vitro infection models replicate the interactions that occur between microorganisms and dynamic antimicrobial exposures in the human body to generate data highly predictive of the clinical efficacy. They are particularly useful for the development new treatment strategies against antimicrobial-resistant pathogens.

Meropenem-vaborbactam restoration of first-line drug efficacy and comparison of meropenem-vaborbactam-moxifloxacin versus BPaL MDR-TB regimen

BACKGROUND

Meropenem in combination with β-lactamase inhibitors (BLIs) and other drugs was tested to identify alternative treatment regimens for multidrug-resistant tuberculosis (MDR-TB).

METHODS

The following were performed: (1) MIC experiments; (2) static time-kill studies (STKs) with different BLIs; and (3) a hollow fibre model system of TB (HFS-TB) studies with meropenem-vaborbactam combined with human equivalent daily doses of 20 mg/kg or 35 mg/kg rifampin, or moxifloxacin 400 mg, or linezolid 600 mg vs. bedaquiline-pretonamid-linezolid (BPaL) for MDR-TB. The studies were performed using Mycobacterium tuberculosis (M. tuberculosis) H37Rv and an MDR-TB clinical strain (named M. tuberculosis 16D) that underwent whole genome sequencing. Exponential decline models were used to calculate the kill rate constant (K) of different HFS-TB regimens.

RESULTS

Whole genome sequencing revealed mutations associated with resistance to rifampin, isoniazid, and cephalosporins. The meropenem-vaborbactam MIC of M. tuberculosis was H37Rv 2 mg/L and > 128 mg/L for M. tuberculosis 16D. Relebactam and vaborbactam improved both the potency and efficacy of meropenem in STKs. Meropenem-vaborbactam alone failed to kill M. tuberculosis 16D but killed below day 0 burden when combined with isoniazid and rifampin, with the moxifloxacin combination being the most effective and outranking bedaquiline and pretomanid. In the HFS-TB, meropenem-vaborbactam-moxifloxacin and BPaL had the highest K (log10 cfu/mL/day) of 0.31 (95% CI 0.17-0.58) and 0.34 (95% CI 0.21-0.56), while meropenem-vaborbactam-rifampin (35 mg/kg) had a K of 0.18 (95% CI 0.12-0.25). The K for meropenem-vaborbactam-moxifloxacin-linezolid demonstrated antagonism.

CONCLUSION

Adding meropenem-vaborbactam could potentially restore the efficacy of isoniazid and rifampin against MDR-TB. The meropenem-vaborbactam-moxifloxacin backbone regimen has implications for creating a new effective MDR-TB regimen.

Pharmacokinetics and pharmacodynamics of anti-tuberculosis drugs: An evaluation of in vitro, in vivo methodologies and human studies

There has been an increased interest in pharmacokinetics and pharmacodynamics (PKPD) of anti-tuberculosis drugs. A better understanding of the relationship between drug exposure, antimicrobial kill and acquired drug resistance is essential not only to optimize current treatment regimens but also to design appropriately dosed regimens with new anti-tuberculosis drugs. Although the interest in PKPD has resulted in an increased number of studies, the actual bench-to-bedside translation is somewhat limited. One of the reasons could be differences in methodologies and outcome assessments that makes it difficult to compare the studies. In this paper we summarize most relevant in vitro, in vivo, in silico and human PKPD studies performed to optimize the drug dose and regimens for treatment of tuberculosis. The in vitro assessment focuses on MIC determination, static time-kill kinetics, and dynamic hollow fibre infection models to investigate acquisition of resistance and killing of Mycobacterium tuberculosis populations in various metabolic states. The in vivo assessment focuses on the various animal models, routes of infection, PK at the site of infection, PD read-outs, biomarkers and differences in treatment outcome evaluation (relapse and death). For human PKPD we focus on early bactericidal activity studies and inclusion of PK and therapeutic drug monitoring in clinical trials. Modelling and simulation approaches that are used to evaluate and link the different data types will be discussed. We also describe the concept of different studies, study design, importance of uniform reporting including microbiological and clinical outcome assessments, and modelling approaches. We aim to encourage researchers to consider methods of assessing and reporting PKPD of anti-tuberculosis drugs when designing studies. This will improve appropriate comparison between studies and accelerate the progress in the field.

Repurposing Cefazolin-Avibactam for the Treatment of Drug Resistant Mycobacterium tuberculosis

Background: While tuberculosis (TB) is curable and preventable, the most effective first-line antibiotics cannot kill multi-drug resistant (MDR) Mycobacterium tuberculosis (Mtb). Therefore, effective drugs are needed to combat MDR-TB, especially in children. Our objective was to repurpose cefazolin for MDR-TB treatment in children using principles of pharmacokinetic/pharmacodynamics (PK/PD).

Methods: Cefazolin minimum inhibitory concentration (MIC) was identified in 17 clinical Mtb strains, with and without combination of the β-lactamase inhibitor, avibactam. Next, dose-ranging studies were performed using the intracellular hollow fiber model of TB (HFS-TB) to identify the optimal cefazolin exposure. Monte Carlo experiments were then performed in 10,000 children for optimal dose identification based on cumulative fraction of response (CFR) and Mtb susceptibility breakpoint in three age-groups.

Results: Avibactam reduced the cefazolin MICs by five tube dilutions. Cefazolin-avibactam demonstrated maximal kill of 4.85 log₁₀ CFU/mL in the intracellular HFS-TB over 28 days. The % time above MIC associated with maximal effect (EC₈₀) was 46.76% (95% confidence interval: 43.04–50.49%) of dosing interval. For 100 mg/kg once or twice daily, the CFR was 8.46 and 61.39% in children <3 years with disseminated TB, 9.70 and 84.07% for 3–5 years-old children, and 17.20 and 76.13% for 12–15 years-old children. The PK/PD-derived susceptibility breakpoint was dose dependent at 1–2 mg/L.

Conclusion: Cefazolin-avibactam combination demonstrates efficacy against both drug susceptible and MDR-TB clinical strains in the HFS-TB and could potentially be used to treat children with tuberculosis. Clinical studies are warranted to validate our findings.

Chemical Classes Presenting Novel Antituberculosis Agents Currently in Different Phases of Drug Development: A 2010-2020 Review

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is a curable airborne disease currently treated using a drug regimen consisting of four drugs. Global TB control has been a persistent challenge for many decades due to the emergence of drug-resistant Mtb strains. The duration and complexity of TB treatment are the main issues leading to treatment failures. Other challenges faced by currently deployed TB regimens include drug-drug interactions, miss-matched pharmacokinetics parameters of drugs in a regimen, and lack of activity against slow replicating sub-population. These challenges underpin the continuous search for novel TB drugs and treatment regimens. This review summarizes new TB drugs/drug candidates under development with emphasis on their chemical classes, biological targets, mode of resistance generation, and pharmacokinetic properties. As effective TB treatment requires a combination of drugs, the issue of drug-drug interaction is, therefore, of great concern; herein, we have compiled drug-drug interaction reports, as well as efficacy reports for drug combinations studies involving antitubercular agents in clinical development.

Population Pharmacokinetics and Bayesian Dose Adjustment to Advance TDM of Anti-TB Drugs

Tuberculosis (TB) is still the number one cause of death due to an infectious disease. Pharmacokinetics and pharmacodynamics of anti-TB drugs are key in the optimization of TB treatment and help to prevent slow response to treatment, acquired drug resistance, and adverse drug effects. The aim of this review was to provide an update on the pharmacokinetics and pharmacodynamics of anti-TB drugs and to show how population pharmacokinetics and Bayesian dose adjustment can be used to optimize treatment. We cover aspects on preclinical, clinical, and population pharmacokinetics of different drugs used for drug-susceptible TB and multidrug-resistant TB. Moreover, we include available data to support therapeutic drug monitoring of these drugs and known pharmacokinetic and pharmacodynamic targets that can be used for optimization of therapy. We have identified a wide range of population pharmacokinetic models for first- and second-line drugs used for TB, which included models built on NONMEM, Pmetrics, ADAPT, MWPharm, Monolix, Phoenix, and NPEM2 software. The first population models were built for isoniazid and rifampicin; however, in recent years, more data have emerged for both new anti-TB drugs, but also for defining targets of older anti-TB drugs. Since the introduction of therapeutic drug monitoring for TB over 3 decades ago, further development of therapeutic drug monitoring in TB next steps will again depend on academic and clinical initiatives. We recommend close collaboration between researchers and the World Health Organization to provide important guideline updates regarding therapeutic drug monitoring and pharmacokinetics/pharmacodynamics.

Mycobacterium tuberculosis sterilizing activity of faropenem, pyrazinamide and linezolid combination and failure to shorten the therapy duration

Background:

Faropenem (F), an orally bioavailable β-lactam, kills Mycobacterium tuberculosis (Mtb) without the help of a β-lactamase inhibitor. This study explored the sterilizing effect of adding F once or twice daily to a linezolid (L) plus pyrazinamide (Z) backbone regimen.

Methods:

In vitro studies were performed using the hollow fiber model of tuberculosis (HFS-TB) to compare the kill rates of: 1) ZL two-drug combination; 2) F administered once daily plus ZL (F₁ZL); 3) F administered twice-daily plus once daily ZL (F₂ZL); 4) F₂ZL with high-dose Z (F₂Z_hiL); 5) standard therapy of isoniazid, rifampin and Z; and 6) non-treated controls. The study was performed over 56 days with three HFS-TB replicates for each regimen.

Results:

Mtb in the non-treated HFS-TB grew at a rate of 0.018 ± 0.007 log₁₀ CFU/mL/day. The exponential kill rates for standard therapy were 6.6–13.2-fold higher than ZL dual therapy. The F₁ZL and F₂ZL regimens ranked third. The pre-existing isoniazid-resistant sub-population in the inoculum (1.34 ± 0.57 log₁₀ CFU/mL) grew to 4.21 ± 0.58 log₁₀ CFU/mL in 56 days in non-treated HFS-TB. However, no isoniazid-resistant sub-population was recorded in any of the FZL combination regimens.

Conclusion:

Due to the slow kill rate compared to standard therapy, FZL regimens are unlikely to shorten therapy duration. Efficacy of these regimens against drug-resistant tuberculosis needs to be determined.

Therapeutic drug monitoring in patients with tuberculosis and concurrent medical problems

INTRODUCTION

Therapeutic drug monitoring (TDM) has been recommended for treatment optimization in tuberculosis (TB) but is only is used in certain countries e.g. USA, Germany, the Netherlands, Sweden and Tanzania. Recently, new drugs have emerged and PK studies in TB are continuing, which contributes further evidence for TDM in TB. The aim of this review is to provide an update on drugs used in TB, treatment strategies for these drugs, and TDM to support broader implementation.

AREAS COVERED

This review describes the different drug classes used for TB, multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB), along with their pharmacokinetics, dosing strategies, TDM and sampling strategies. Moreover, the review discusses TDM for patient TB and renal or liver impairment, patients co-infected with HIV or hepatitis, and special patient populations - children and pregnant women.

EXPERT OPINION

TB treatment has a long history of using 'one size fits all.' This has contributed to treatment failures, treatment relapses, and the selection of drug-resistant isolates. While challenging in resource-limited circumstances, TDM offers the clinician the opportunity to individualize and optimize treatment early in treatment. This approach may help to refine treatment and thereby reduce adverse effects and poor treatment outcomes. Funding, training, and randomized controlled trials are needed to advance the use of TDM for patients with TB.

Tuberculosis and beta-lactam antibiotics

Tuberculosis (TB) is one of the oldest health problems in the world and it remains unresolved. Multidrug-resistant-TB and extensively resistant-TB are a serious problem for control programs. The evaluation of available antibiotics has gained importance in recent years for the treatment of resistant TB. Beta-lactam antibiotics inhibit cell wall biosynthesis in the bacteria; the presence of beta-lactamase enzyme in TB bacilli raises the question of whether this group of antibiotics can be used in treatment. As a result, it has been reported that the combination of beta-lactam antibiotics with beta-lactamase is effective against Mycobacterium tuberculosis both in vitro and in vivo. The aim of this article is to review and discuss up-to-date knowledge and future perspective on beta-lactam antibiotics and TB.

Pharmacologic management of Mycobacterium ulcerans infection

INTRODUCTION

Pharmacological treatment of Buruli ulcer (Mycobacterium ulcerans infection; BU) is highly effective, as shown in two randomized trials in Africa.

AREAS COVERED

We review BU drug treatment - in vitro, in vivo and clinical trials (PubMed: '(Buruli OR (Mycobacterium AND ulcerans)) AND (treatment OR therapy).' We also highlight the pathogenesis of M. ulcerans infection that is dominated by mycolactone, a secreted exotoxin, that causes skin and soft tissue necrosis, and impaired immune response and tissue repair. Healing is slow, due to the delayed wash-out of mycolactone. An array of repurposed tuberculosis and leprosy drugs appears effective in vitro and in animal models. In clinical trials and observational studies, only rifamycins (notably, rifampicin), macrolides (notably, clarithromycin), aminoglycosides (notably, streptomycin) and fluoroquinolones (notably, moxifloxacin, and ciprofloxacin) have been tested.

EXPERT OPINION

A combination of rifampicin and clarithromycin is highly effective but lesions still take a long time to heal. Novel drugs like telacebec have the potential to reduce treatment duration but this drug may remain unaffordable in low-resourced settings. Research should address ulcer treatment in general; essays to measure mycolactone over time hold promise to use as a readout for studies to compare drug treatment schedules for larger lesions of Buruli ulcer.

The Role of Fluoroquinolones in the Treatment of Tuberculosis in 2019

The inability to use powerful antituberculosis drugs in an increasing number of patients seems to be the biggest threat towards global tuberculosis (TB) elimination. Simplified, shorter and preferably less toxic drug regimens are being investigated for pulmonary TB to counteract emergence of drug resistance. Intensified regimens with high-dose anti-TB drugs during the first weeks of treatment are being investigated for TB meningitis to increase the survival rate among these patients. Moxifloxacin, gatifloxacin and levofloxacin are seen as core agents in case of resistance or intolerance against first-line anti-TB drugs. However, based on their pharmacokinetics (PK) and pharmacodynamics (PD), these drugs are also promising for TB meningitis and might perhaps have the potential to shorten pulmonary TB treatment if dosing could be optimized. We prepared a comprehensive summary of clinical trials investigating the outcome of TB regimens based on moxifloxacin, gatifloxacin and levofloxacin in recent years. In the majority of clinical trials, treatment success was not in favour of these drugs compared to standard regimens. By discussing these results, we propose that incorporation of extended PK/PD analysis into the armamentarium of drug-development tools is needed to clarify the role of moxifloxacin, gatifloxacin and levofloxacin for TB, using the right dose. In addition, to prevent failure of treatment or emergence of drug-resistance, PK and PD variability advocates for concentration-guided dosing in patients at risk for too low a drug-exposure.

Evaluation of Carbapenems for Treatment of Multi- and Extensively Drug-Resistant Mycobacterium tuberculosis

Multi- and extensively drug-resistant tuberculosis (M/XDR-TB) has become an increasing threat not only in countries where the TB burden is high but also in affluent regions, due to increased international travel and globalization. Carbapenems are earmarked as potentially active drugs for the treatment of Mycobacterium tuberculosis To better understand the potential of carbapenems for the treatment of M/XDR-TB, the aim of this review was to evaluate the literature on currently available in vitro, in vivo, and clinical data on carbapenems in the treatment of M. tuberculosis and to detect knowledge gaps, in order to target future research. In February 2018, a systematic literature search of PubMed and Web of Science was performed. Overall, the results of the studies identified in this review, which used a variety of carbapenem susceptibility tests on clinical and laboratory strains of M. tuberculosis, are consistent. In vitro, the activity of carbapenems against M. tuberculosis is increased when used in combination with clavulanate, a BLaC inhibitor. However, clavulanate is not commercially available alone, and therefore, it is impossible in practice to prescribe carbapenems in combination with clavulanate at this time. Few in vivo studies have been performed, including one prospective, two observational, and seven retrospective clinical studies to assess the effectiveness, safety, and tolerability of three different carbapenems (imipenem, meropenem, and ertapenem). We found no clear evidence at the present time to select one particular carbapenem among the different candidate compounds to design an effective M/XDR-TB regimen. Therefore, more clinical evidence and dose optimization substantiated by hollow-fiber infection studies are needed to support repurposing carbapenems for the treatment of M/XDR-TB.

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.

The Sterilizing Effect of Intermittent Tedizolid for Pulmonary Tuberculosis

Background

Linezolid exhibits remarkable sterilizing effect in tuberculosis; however, a large proportion of patients develop serious adverse events. The congener tedizolid could have a better side-effect profile, but its sterilizing effect potential is unknown.

Methods

We performed a 42-day tedizolid exposure-effect and dose-fractionation study in the hollow fiber system model of tuberculosis for sterilizing effect, using human-like intrapulmonary pharmacokinetics. Bacterial burden was examined using time to positivity (TTP) and colony-forming units (CFUs). Exposure-effect was examined using the inhibitory sigmoid maximal kill model. The exposure mediating 80% of maximal kill (EC80) was defined as the target exposure, and the lowest dose to achieve EC80 was identified in 10000-patient Monte Carlo experiments. The dose was also examined for probability of attaining concentrations associated with mitochondrial enzyme inhibition.

Results

At maximal effect, tedizolid monotherapy totally eliminated 7.1 log10 CFU/mL Mycobacterium tuberculosis over 42 days; however, TTP still demonstrated some growth. Once-weekly tedizolid regimens killed as effectively as daily regimens, with an EC80 free drug 0- to 24-hour area under the concentration-time curve-to-minimum inhibitory concentration (MIC) ratio of 200. An oral tedizolid of 200 mg/day achieved the EC80 in 92% of 10000 patients. The susceptibility breakpoint was an MIC of 0.5 mg/L. The 200 mg/day dose did not achieve concentrations associated with mitochondrial enzyme inhibition.

Conclusions

Tedizolid exhibits dramatic sterilizing effect and should be examined for pulmonary tuberculosis. A tedizolid dose of 200 mg/day or 700 mg twice a week is recommended for testing in patients; the intermittent tedizolid dosing schedule could be much safer than daily linezolid.

Meropenem Combined with Ciprofloxacin Combats Hypermutable Pseudomonas aeruginosa from Respiratory Infections of Cystic Fibrosis Patients

Hypermutable Pseudomonas aeruginosa organisms are prevalent in chronic respiratory infections and have been associated with reduced lung function in cystic fibrosis (CF); these isolates can become resistant to all antibiotics in monotherapy. This study aimed to evaluate the time course of bacterial killing and resistance of meropenem and ciprofloxacin in combination against hypermutable and nonhypermutable P. aeruginosa Static concentration time-kill experiments over 72 h assessed meropenem and ciprofloxacin in mono- and combination therapies against PAO1 (nonhypermutable), PAOΔmutS (hypermutable), and hypermutable isolates CW8, CW35, and CW44 obtained from CF patients with chronic respiratory infections. Meropenem (1 or 2 g every 8 h [q8h] as 3-h infusions and 3 g/day as a continuous infusion) and ciprofloxacin (400 mg q8h as 1-h infusions) in monotherapies and combinations were further evaluated in an 8-day hollow-fiber infection model study (HFIM) against CW44. Concentration-time profiles in lung epithelial lining fluid reflecting the pharmacokinetics in CF patients were simulated and counts of total and resistant bacteria determined. All data were analyzed by mechanism-based modeling (MBM). In the HFIM, all monotherapies resulted in rapid regrowth with resistance at 48 h. The maximum daily doses of 6 g meropenem (T_>MIC of 80% to 88%) and 1.2 g ciprofloxacin (area under the concentration-time curve over 24 h in the steady state divided by the MIC [AUC/MIC], 176), both given intermittently, in monotherapy failed to suppress regrowth and resulted in substantial emergence of resistance (≥7.6 log₁₀ CFU/ml resistant populations). The combination of these regimens achieved synergistic killing and suppressed resistance. MBM with subpopulation and mechanistic synergy yielded unbiased and precise curve fits. Thus, the combination of 6 g/day meropenem plus ciprofloxacin holds promise for future clinical evaluation against infections by susceptible hypermutable P. aeruginosa.

Pharmacokinetics of β-Lactam Antibiotics: Clues from the Past To Help Discover Long-Acting Oral Drugs in the Future

β-Lactams represent perhaps the most important class of antibiotics yet discovered. However, despite many years of active research, none of the currently approved drugs in this class combine oral activity with long duration of action. Recent developments suggest that new β-lactam antibiotics with such a profile would have utility in the treatment of tuberculosis. Consequently, the historical β-lactam pharmacokinetic data have been compiled and analyzed to identify possible directions and drug discovery strategies aimed toward new β-lactam antibiotics with this profile.

Optimization and Evaluation of Piperacillin-Tobramycin Combination Dosage Regimens against Pseudomonas aeruginosa for Patients with Altered Pharmacokinetics via the Hollow-Fiber Infection Model and Mechanism-Based Modeling

Augmented renal clearance (ARC) in critically ill patients can result in suboptimal drug exposures and treatment failure. Combination dosage regimens accounting for ARC have never been optimized and evaluated against Pseudomonas aeruginosa by use of the hollow-fiber infection model (HFIM). Using a P. aeruginosa isolate from a critically ill patient and static-concentration time-kill experiments (SCTKs), we studied clinically relevant piperacillin and tobramycin concentrations, alone and in combinations, against two inocula (10^5.8 and 10^7.6 CFU/ml) over 72 h. We subsequently evaluated the effects of optimized piperacillin (4 g every 4 h [q4h], given as 0.5-h infusions) plus tobramycin (5 mg/kg of body weight q24h, 7 mg/kg q24h, or 10 mg/kg q48h, given as 0.5-h infusions) regimens on killing and regrowth in the HFIM, simulating a creatinine clearance of 250 ml/min. Mechanism-based modeling was performed in S-ADAPT. In SCTKs, piperacillin plus tobramycin (except combinations with 8 mg/liter tobramycin and against the low inoculum) achieved synergistic killing (≥2 log₁₀ versus the most active monotherapy at 48 h and 72 h) and prevented regrowth. Piperacillin monotherapy (4 g q4h) in the HFIM provided 2.4-log₁₀ initial killing followed by regrowth at 24 h and resistance emergence. Tobramycin monotherapies displayed rapid initial killing (≥5 log₁₀ at 13 h) followed by extensive regrowth. As predicted by mechanism-based modeling, the piperacillin plus tobramycin dosage regimens were synergistic and provided ≥5-log₁₀ killing with resistance suppression over 8 days in the HFIM. Optimized piperacillin-tobramycin regimens provided significant bacterial killing and suppressed resistance emergence. These regimens appear to be highly promising for effective and early treatment, even in the near-worst-case scenario of ARC.

Pharmacokinetics of 2,000 Milligram Ertapenem in Tuberculosis Patients

Ertapenem is a carbapenem antibiotic with activity against Mycobacterium tuberculosis Dose simulations in a hollow-fiber infection model showed that 2,000 mg once daily is an appropriate dose to be tested in clinical studies. Before using this dose in a phase II study, the aim of this prospective pharmacokinetic study was to confirm the pharmacokinetics of 2,000 mg once daily in tuberculosis (TB) patients. Twelve TB patients received a single intravenous dose of 2,000 mg ertapenem as a 30-min infusion. Blood samples were collected at 0, 0.5, 1, 2, 3, 4, 8, 12, and 24 h postadministration. Drug concentrations were measured using a validated liquid chromatography-tandem mass spectrometry assay. A large interindividual variation in the pharmacokinetics of ertapenem was observed. The median (interquartile range) area under the plasma concentration-time curve to infinity (AUC_0-∞) was 2,032 (1,751 to 2,346) mg · h/liter, the intercompartmental clearance (CL₁₂) was 1.941 (0.979 to 2.817) liters/h, and the volume of distribution in the central compartment (V₁) was 1.514 (1.064 to 2.210) liters. A more than dose-proportional increase in AUC was observed compared to results reported for 1,000 mg ertapenem in multidrug-resistant TB patients. Based on a MIC of 1.0 mg/liter, 11 out of 12 patients would have reached the target value of unbound drug exceeding the MIC over 40% of the time (f40% T>MIC). In conclusion, this study shows that 2,000 mg ertapenem once daily in TB patients reached the expected f40% T>MIC for most of the patients, and exploration in a phase 2 study can be advocated.

Tuberculosis: progress and advances in development of new drugs, treatment regimens, and host-directed therapies

Tuberculosis remains the world's leading cause of death from an infectious disease, responsible for an estimated 1 674 000 deaths annually. WHO estimated 600 000 cases of rifampicin-resistant tuberculosis in 2016-of which 490 000 were multidrug resistant (MDR), with less than 50% survival after receiving recommended treatment regimens. Concerted efforts of stakeholders, advocates, and researchers are advancing further development of shorter course, more effective, safer, and better tolerated treatment regimens. We review the developmental pipeline and landscape of new and repurposed tuberculosis drugs, treatment regimens, and host-directed therapies (HDTs) for drug-sensitive and drug-resistant tuberculosis. 14 candidate drugs for drug-susceptible, drug-resistant, and latent tuberculosis are in clinical stages of drug development; nine are novel in phase 1 and 2 trials, and three new drugs are in advanced stages of development for MDR tuberculosis. Specific updates are provided on clinical trials of bedaquiline, delamanid, pretomanid, and other licensed or repurposed drugs that are undergoing investigation, including trials aimed at shortening duration of tuberculosis treatment, improving treatment outcomes and patient adherence, and reducing toxic effects. Ongoing clinical trials for shortening tuberculosis treatment duration, improving treatment outcomes in MDR tuberculosis, and preventing disease in people with latent tuberculosis infection are reviewed. A range of HDTs and immune-based treatments are under investigation as adjunctive therapy for shortening duration of therapy, preventing permanent lung injury, and improving treatment outcomes of MDR tuberculosis. We discuss the HDT development pipeline, ongoing clinical trials, and translational research efforts for adjunct tuberculosis treatment.

Antibacterial and Sterilizing Effect of Benzylpenicillin in Tuberculosis

The modern chemotherapy era started with Fleming's discovery of benzylpenicillin. He demonstrated that benzylpenicillin did not kill Mycobacterium tuberculosis In this study, we found that >64 mg/liter of static benzylpenicillin concentrations killed 1.16 to 1.43 log10 CFU/ml below starting inoculum of extracellular and intracellular M. tuberculosis over 7 days. When we added the β-lactamase inhibitor avibactam, benzylpenicillin maximal kill (Emax) of extracellular log-phase-growth M. tuberculosis was 6.80 ± 0.45 log10 CFU/ml at a 50% effective concentration (EC50) of 15.11 ± 2.31 mg/liter, while for intracellular M. tuberculosis it was 2.42 ± 0.14 log10 CFU/ml at an EC50 of 6.70 ± 0.56 mg/liter. The median penicillin (plus avibactam) MIC against South African clinical M. tuberculosis strains (80% either multidrug or extensively drug resistant) was 2 mg/liter. We mimicked human-like benzylpenicillin and avibactam concentration-time profiles in the hollow-fiber model of tuberculosis (HFS-TB). The percent time above the MIC was linked to effect, with an optimal exposure of ≥65%. At optimal exposure in the HFS-TB, the bactericidal activity in log-phase-growth M. tuberculosis was 1.44 log10 CFU/ml/day, while 3.28 log10 CFU/ml of intracellular M. tuberculosis was killed over 3 weeks. In an 8-week HFS-TB study of nonreplicating persistent M. tuberculosis, penicillin-avibactam alone and the drug combination of isoniazid, rifampin, and pyrazinamide both killed >7.0 log10 CFU/ml. Monte Carlo simulations of 10,000 preterm infants with disseminated disease identified an optimal dose of 10,000 U/kg (of body weight)/h, while for pregnant women or nonpregnant adults with pulmonary tuberculosis the optimal dose was 25,000 U/kg/h, by continuous intravenous infusion. Penicillin-avibactam should be examined for effect in pregnant women and infants with drug-resistant tuberculosis, to replace injectable ototoxic and teratogenic second-line drugs.