Tedizolid is highly bactericidal in the treatment of pulmonary Mycobacterium avium complex disease

Ceftriaxone Efficacy for Mycobacterium avium Complex Lung Disease in the Hollow Fiber and Translation to Sustained Sputum Culture Conversion in Patients

BACKGROUND

Only 35.6%-50.8% of patients with Mycobacterium avium complex (MAC) pulmonary disease achieve sustained sputum culture conversion (SSCC) on treatment with the azithromycin-ethambutol-rifabutin standard of care (SOC). We tested the efficacy of ceftriaxone, a β-lactam with a lung-to-serum penetration ratio of 12.18-fold.

METHODS

We mimicked lung concentration-time profiles of 7 ceftriaxone once-daily doses for 28 days in the hollow fiber system model of intracellular MAC (HFS-MAC). Monte Carlo experiments were used for dose selection. We also compared once-daily ceftriaxone monotherapy to 3-drug SOC against 5 MAC clinical isolates in HFS-MAC using γ (kill) slopes, and translated to SSCC rates.

RESULTS

Ceftriaxone killed 1.02-3.82 log10 colony-forming units (CFU)/mL, at optimal dose of 2 g once-daily. Ceftriaxone killed all 5 strains below day 0 versus 2 of 5 for SOC. The median γ (95% confidence interval [CI]) was 0.49 (.47-.52) log10 CFU/mL/day for ceftriaxone and 0.38 (.34-.43) log10 CFU/mL/day for SOC. In patients, the SOC was predicted to achieve SSCC rates (CI) of 39.3% (36%-42%) at 6 months. The SOC SSCC was 50% at 8.18 (3.64-27.66) months versus 3.58 (2.20-7.23) months for ceftriaxone, shortening time to SSCC 2.35-fold.

CONCLUSIONS

Ceftriaxone is a promising agent for creation of short-course chemotherapy.

Correlation of drug exposure and bacterial susceptibility with treatment response for Mycobacterium avium complex lung disease: protocol for a prospective observational cohort study

INTRODUCTION

The burden of Mycobacterium avium complex (MAC) lung disease is increasing globally and treatment outcome is in general poor. Therapeutic drug monitoring has the potential to improve treatment outcome by ensuring adequate drug exposure. However, very limited population-based studies exist for MAC lung disease. This study aims to describe the distribution of drug exposure for key antimycobacterial drugs at population level, and to analyse them in relationship to treatment outcome in patients with MAC lung disease.

METHODS AND ANALYSIS

A prospective cohort aiming to include 100 adult patients diagnosed with and treated for MAC lung disease will be conducted in Shanghai Pulmonary Hospital, China. Blood samples will be collected after 1 month MAC treatment for measurement of macrolides, rifamycin, ethambutol, amikacin and/or fluoroquinolones, using a validated liquid-chromatography tandem mass spectrometry method. Respiratory samples will be collected at inclusion and once every 3 months for mycobacterial culture until treatment completion. Minimum inhibitory concentration (MIC) determination will be performed using a commercial broth microdilution plate. In addition to mycobacterial culture, disease severity and clinical improvement will be assessed from the perspective of lung function, radiological presentation and self-reported quality of life. Whole genome sequencing will be performed for any longitudinal isolates with significant change of MIC to explore the emergence of drug resistance-conferring mutations. The relationship between drug exposure and treatment outcome will be analysed and potential confounders will be considered for adjustment in multivariable models. Meanwhile, the associations between drug exposure in relation to MIC and markers of treatment response will be explored using Cox proportional hazards or binary logistic regression models, as appropriate.

ETHICS AND DISSEMINATION

This study has been approved by the ethics committee of Shanghai Pulmonary Hospital (No. K22-149Z). Written and oral informed consent will be obtained from all participants. The study results will be submitted to a peer-reviewed journal.

TRIAL REGISTERATION NUMBER

NCT05824988.

New Antimicrobials for Gram-Positive Sustained Infections: A Comprehensive Guide for Clinicians

Antibiotic resistance is a public health problem with increasingly alarming data being reported. Gram-positive bacteria are among the protagonists of severe nosocomial and community infections. The objective of this review is to conduct an extensive examination of emerging treatments for Gram-positive infections including ceftobiprole, ceftaroline, dalbavancin, oritavancin, omadacycline, tedizolid, and delafloxacin. From a methodological standpoint, a comprehensive analysis on clinical trials, molecular structure, mechanism of action, microbiological targeting, clinical use, pharmacokinetic/pharmacodynamic features, and potential for therapeutic drug monitoring will be addressed. Each antibiotic paragraph is divided into specialized microbiological, clinical, and pharmacological sections, including detailed and appropriate tables. A better understanding of the latest promising advances in the field of therapeutic options could lead to the development of a better approach in managing antimicrobial therapy for multidrug-resistant Gram-positive pathogens, which increasingly needs to be better stratified and targeted.

In vitro Susceptibility of Nontuberculous Mycobacteria to Tedizolid

Objective

Nontuberculous mycobacteria (NTM) can cause pulmonary and extrapulmonary diseases. Tedizolid (TZD) is a new oxazolidinone with in vitro activity against NTM such as Mycobacterium avium complex (MAC), Mycobacterium fortuitum, and Mycobacterium abscessus complex. The aim of this study was to evaluate the TZD susceptibility profiles of clinical isolates of NTM.

Methods

The microdilution method was used to identify the minimum inhibitory concentration (MIC) of TZD and linezolid (LZD) for 133 clinical NTM isolates. Broth microdilution chequerboard assays were used to investigate the synergistic effects of TZD and three antibiotics on two reference isolates and eleven clinical isolates of NTM.

Results

The TZD MIC₅₀ and MIC₉₀ for M. abscessus complex were 2 and 4 μg/mL, 16 and >32 μg/mL for MAC, respectively. TZD exhibited lower MICs than that of LZD for most NTM, which were positively correlated. Due to the high MIC values of TZD against MAC, it is necessary to conduct drug sensitivity tests before TZD administration. TZD-clarithromycin combination had synergistic response on M. abscessus complex in 3 of the 8 isolates, which lasted only 3-5 days. TZD-cefoxitin had synergistic effect against all five M. fortuitum isolates.

Conclusion

Our study demonstrates that TZD had greater in vitro potency than LZD, and synergy studies suggested that TZD may be an important component of multi-drug treatment regimen.

In vitro assessment of 17 antimicrobial agents against clinical Mycobacterium avium complex isolates

Background

Recently, Mycobacterium avium complex (MAC) infections have been increasing, especially in immunocompromised and older adults. The rapid increase has triggered a global health concern due to limited therapeutic strategies and adverse effects caused by long-term medication. To provide more evidence for the treatment of MAC, we studied the in vitro inhibitory activities of 17 antimicrobial agents against clinical MAC isolates.

Results

A total of 111 clinical MAC isolates were enrolled in the study and they were identified as M. intracellulare, M. avium, M. marseillense, M. colombiense, M. yongonense, and two isolates could not be identified at the species level. MAC strains had relatively low (0–21.6%) resistance to clarithromycin, amikacin, bedaquiline, rifabutin, streptomycin, and clofazimine, and the resistant rates to isoniazid, rifampin, linezolid, doxycycline, and ethionamide were very high (72.1–100%). In addition, M. avium had a significantly higher resistance rate than that of M. intracellulare for ethambutol (92.3% vs 40.7%, P < 0.001), amikacin (15.4% vs 1.2%, P = 0.049), and cycloserine (69.2% vs 25.9%, P = 0.004).

Conclusions

Our results supported the current usage of macrolides, rifabutin, and aminoglycosides in the regimens for MAC infection, and also demonstrated the low resistance rate against new drugs, such as clofazimine, tedizolid, and bedaquiline, suggesting the possible implementation of these drugs in MAC treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02582-2.

Pharmacokinetics and Pharmacodynamics of Tedizolid

Tedizolid is an oxazolidinone antibiotic with high potency against Gram-positive bacteria and currently prescribed in bacterial skin and skin-structure infections. The aim of the review was to summarize and critically review the key pharmacokinetic and pharmacodynamic aspects of tedizolid. Tedizolid displays linear pharmacokinetics with good tissue penetration. In in vitro susceptibility studies, tedizolid exhibits activity against the majority of Gram-positive bacteria (minimal inhibitory concentration [MIC] of ≤ 0.5 mg/L), is four-fold more potent than linezolid, and has the potential to treat pathogens being less susceptible to linezolid. Area under the unbound concentration-time curve (fAUC) related to MIC (fAUC/MIC) was best correlated with efficacy. In neutropenic mice, fAUC/MIC of ~ 50 and ~ 20 induced bacteriostasis in thigh and pulmonary infection models, respectively, at 24 h. The presence of granulocytes augmented its antibacterial effect. Hence, tedizolid is currently not recommended for immunocompromised patients. Clinical investigations with daily doses of 200 mg for 6 days showed non-inferiority to twice-daily dosing of linezolid 600 mg for 10 days in patients with acute bacterial skin and skin-structure infections. In addition to its use in skin and skin-structure infections, the high pulmonary penetration makes it an attractive option for respiratory infections including Mycobacterium tuberculosis. Resistance against tedizolid is rare yet effective antimicrobial surveillance and defining pharmacokinetic/pharmacodynamic targets for resistance suppression are needed to guide dosing strategies to suppress resistance development.

Importance and Reality of TDM for Antibiotics Not Covered by Insurance in Japan

Under the Japanese health insurance system, medicines undergoing therapeutic drug monitoring (TDM) can be billed for medical fees if they meet the specified requirements. In Japan, TDM of vancomycin, teicoplanin, aminoglycosides, and voriconazole, which are used for the treatment of infectious diseases, is common practice. This means the levels of antibiotics are measured in-house using chromatography or other methods. In some facilities, the blood and/or tissue concentrations of other non-TDM drugs are measured by HPLC and are applied to treatment, which is necessary for personalized medicine. This review describes personalized medicine based on the use of chromatography as a result of the current situation in Japan.

OUP accepted manuscript

Objectives

The standard of care (SOC) for the treatment of pulmonary Mycobacterium avium complex (MAC) disease (clarithromycin, rifabutin, and ethambutol) achieves sustained sputum conversion rates of only 54%. Thus, new treatments should be prioritized.

Methods

We identified the omadacycline MIC against one laboratory MAC strain and calculated drug half life in solution, which we compared with measured MAC doubling times. Next, we performed an omadacycline hollow fibre system model of intracellular MAC (HFS-MAC) exposure–effect study, as well as the three-drug SOC, using pharmacokinetics achieved in patient lung lesions. Data was analysed using bacterial kill slopes (γ-slopes) and inhibitory sigmoid E_max bacterial burden versus exposure analyses. Monte Carlo experiments (MCE) were used to identify the optimal omadacycline clinical dose.

Results

Omadacycline concentration declined in solution with a half-life of 27.7 h versus a MAC doubling time of 16.3 h, leading to artefactually high MICs. Exposures mediating 80% of maximal effect changed up to 8-fold depending on sampling day with bacterial burden versus exposure analyses, while γ-slope-based analyses gave a single robust estimate. The highest omadacycline monotherapy γ-slope was −0.114 (95% CI: −0.141 to −0.087) (r^2 =0.98) versus −0.114 (95% CI: −0.133 to −0.094) (r²= 0.99) with the SOC. MCEs demonstrated that 450 mg of omadacycline given orally on the first 2 days followed by 300 mg daily would achieve the AUC_0-24 target of 39.67 mg·h/L.

Conclusions

Omadacycline may be a potential treatment option for pulmonary MAC, possibly as a back-bone treatment for a new MAC regimen and warrants future study in treatment of this disease.

Improving the Drug Development Pipeline for Mycobacteria: Modelling Antibiotic Exposure in the Hollow Fibre Infection Model

Mycobacterial infections are difficult to treat, requiring a combination of drugs and lengthy treatment times, thereby presenting a substantial burden to both the patient and health services worldwide. The limited treatment options available are under threat due to the emergence of antibiotic resistance in the pathogen, hence necessitating the development of new treatment regimens. Drug development processes are lengthy, resource intensive, and high-risk, which have contributed to market failure as demonstrated by pharmaceutical companies limiting their antimicrobial drug discovery programmes. Pre-clinical protocols evaluating treatment regimens that can mimic in vivo PK/PD attributes can underpin the drug development process. The hollow fibre infection model (HFIM) allows for the pathogen to be exposed to a single or a combination of agents at concentrations achieved in vivo-in plasma or at infection sites. Samples taken from the HFIM, depending on the analyses performed, provide information on the rate of bacterial killing and the emergence of resistance. Thereby, the HFIM is an effective means to investigate the efficacy of a drug combination. Although applicable to a wide variety of infections, the complexity of anti-mycobacterial drug discovery makes the information available from the HFIM invaluable as explored in this review.

Development of a simple method for measuring tedizolid concentration in human serum using HPLC with a fluorescent detector

The objective of the present study was to develop a method to measure tedizolid (TZD) concentration for studying target concentration intervention, pharmacokinetics, and pharmacodynamics of TZD. We established a high-performance liquid chromatography-fluorescence detector assay to measure the TZD concentration in serum for clinical application. Chromatographic separation was carried out on a 5 μm octadecyl silane hypersil column 150 mm × 4.6 mm. The mobile phase consisted of 0.1 M phosphoric acid and methanol (60:40, pH 7.0). Detection was performed at 300 nm and 340 nm for the excitation and emission wavelengths, respectively. The average retention times of TZD and the internal standard were 12.9 and 8.8 min, respectively. High linearity was exhibited over a concentration range of 0.025 to 10.0 μg/mL for TZD (R2 > 0.999). The intra- and inter-assay accuracies of TZD were 99.2% to 107.0% and 99.2% to 107.7%, respectively. The lower limit of quantitation and the lower limit of detection for TZD measurement were 0.025 and 0.01 μg/mL, respectively. The extraction recoveries of TZD were 100.4% to 114.1%.The high-performance liquid chromatography method developed in this study could separate the analytes with a single eluent (isocratic system), within a total run time of 15 min. Both TZD and IS were well separated, without interference from the peaks. Sharp peaks were observed in the chromatograms; problems such as double peaks, shoulder peaks, and broadened peaks were not observed. The proposed method showed acceptable analytical performance and could be used to evaluate serum TZD concentrations in patients.

In Silico Identification of Possible Inhibitors for Protein Kinase B (PknB) of Mycobacterium tuberculosis

With tuberculosis still being one of leading causes of death in the world and the emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb), researchers have been seeking to find further therapeutic strategies or more specific molecular targets. PknB is one of the 11 Ser/Thr protein kinases of Mtb and is responsible for phosphorylation-mediated signaling, mainly involved in cell wall synthesis, cell division and metabolism. With the amount of structural information available and the great interest in protein kinases, PknB has become an attractive target for drug development. This work describes the optimization and application of an in silico computational protocol to find new PknB inhibitors. This multi-level computational approach combines protein-ligand docking, structure-based virtual screening, molecular dynamics simulations and free energy calculations. The optimized protocol was applied to screen a large dataset containing 129,650 molecules, obtained from the ZINC/FDA-Approved database, Mu.Ta.Lig Virtual Chemotheca and Chimiothèque Nationale. It was observed that the most promising compounds selected occupy the adenine-binding pocket in PknB, and the main interacting residues are Leu17, Val26, Tyr94 and Met155. Only one of the compounds was able to move the active site residues into an open conformation. It was also observed that the P-loop and magnesium position loops change according to the characteristics of the ligand. This protocol led to the identification of six compounds for further experimental testing while also providing additional structural information for the design of more specific and more effective derivatives.

Determination of Tedizolid in Bacterial Growth Medium Mueller-Hinton Broth by High-Performance Liquid Chromatography and Its Application to an In Vitro Study in the Hollow-Fiber Infection Model

Pharmacokinetic/pharmacodynamic (PKPD) studies of anti-infectives are frequently performed in in vitro infection models where accurate quantification of antibiotic concentrations in bacterial growth media is crucial to establish PK/PD relationships. Here, a sensitive and rapid high-performance liquid chromatography (HPLC) method was developed to quantify tedizolid (TDZ) in the bacterial growth medium Mueller-Hinton broth (MHB). Matrix components were separated by direct protein precipitation with methanol (1:1). The chromatographic separation was carried out in a Dionex Ultimate 3000 HPLC system using an Accucore® C-18 RPMS HPLC column (2.6 µm, 100 × 2.1 mm) using isocratic elution with 25% acetonitrile and 75% of 0.1% formic acid. The lower limit of quantification was 0.03 mg/L when measured at 300 nm. Following relevant European Medicine Agency guidelines, the method was successfully validated for linearity, selectivity, recovery, inter- and intra-day precision, and accuracy and stability. When applied to in vitro PKPD studies, the method successfully quantified a range of TDZ concentration (Cmin, 0.09-Cmax, 0.65 mg/L) in MHB. The analyzed concentrations were in line with the planned PK profiles. The application of the developed method to quantify TDZ in MHB in in vitro PKPD studies is warranted.

Standard therapy of Mycobacterium avium complex pulmonary disease shows limited efficacy in an open source hollow fibre system that simulates human plasma and epithelial lining fluid pharmacokinetics

OBJECTIVES

Mycobacterium avium complex (MAC) bacteria can cause chronic pulmonary disease (PD). Current treatment regimens of azithromycin, ethambutol and rifampicin have culture conversion rates of around 65%. Dynamic, preclinical models to assess the efficacy of treatment regimens are important to guide clinical trial development. The hollow fibre system (HFS) has been applied but reports lack experimental details.

METHODS

We simulated the human pharmacokinetics of azithromycin, ethambutol and rifampicin both in plasma and epithelial lining fluid (ELF) in a HFS, exposing THP-1 cells infected with M. avium to the triple-drug regimen for 3 weeks. We accounted for drug-drug interactions and protein-binding and provide all laboratory protocols. We differentiated the effects on the intracellular and extracellular mycobacterial population.

RESULTS

The antibiotic concentrations in the HFS accurately reflected the time to peak concentration (T_max), the peak concentration (C_max) and half-life of azithromycin, rifampicin and ethambutol in plasma and ELF reported in literature. We find that plasma drug concentrations fail to hold the MAC bacterial load static (ΔLog10 CFU/mL_{Control:Regimen} = 0.66 ± 0.76 and 0.45 ± 0.28 at 3 and 21 days); ELF concentrations do hold the bacterial load static for 3 days and inhibit bacterial growth for the duration of the experiment (ΔLog10 CFU/mL_{Control:Regimen} = 1.1 ± 0.1 and 1.64 ± 0.59 at 3 and 21 days).

DISCUSSION

In our model, the current therapy against MAC is ineffective, even when accounting for antibiotic accumulation at the site of infection and intracellularly. New treatment regimens need to be developed and be compared with currently recommended regimens in dynamic models prior to clinical evaluation. With the publication of all protocols we aim to open this technology to new users.

Is there a role for tedizolid in the treatment of non-tuberculous mycobacterial disease?

Background

Pulmonary infections caused by non-tuberculous mycobacteria (NTM) are hard to treat and have low cure rates despite intensive multidrug therapy.

Objectives

To assess the feasibility of tedizolid, a new oxazolidinone, for the treatment of Mycobacterium avium and Mycobacterium abscessus.

Methods

We determined MICs of tedizolid for 113 isolates of NTM. Synergy with key antimycobacterial drugs was assessed using the chequerboard method and calculation of the FIC index (FICI). We performed time–kill kinetics assays of tedizolid alone and combined with amikacin for M. abscessus and with ethambutol for M. avium. Human macrophages were infected with M. abscessus and M. avium and subsequently treated with tedizolid; intracellular and extracellular cfu were quantified over time.

Results

NTM isolates generally had a lower MIC of tedizolid than of linezolid. FICIs were lowest between tedizolid and amikacin for M. abscessus (FICI = 0.75) and between tedizolid and ethambutol for M. avium (FICI = 0.72). Clarithromycin and tedizolid showed initial synergy, which was abrogated by erm(41)-induced macrolide resistance (FICI = 0.53). Tedizolid had a weak bacteriostatic effect on M. abscessus and combination with amikacin slightly prolonged its effect. Tedizolid had concentration-dependent activity against M. avium and its efficacy was enhanced by ethambutol. Both combinations had a concentration-dependent synergistic effect. Tedizolid could inhibit the intracellular bacterial population of both M. avium and M. abscessus.

Conclusions

Tedizolid should be further investigated in pharmacodynamic studies and clinical trials for M. avium complex pulmonary disease. It is less active against M. abscessus, but still promising.

Comparison of Rifamycins for Efficacy Against Mycobacterium avium Complex and Resistance Emergence in the Hollow Fiber Model System

Rifamycins are integral part of the combination regimen for treatment of pulmonary Mycobacterium avium-complex [MAC] infection, but different practitioners prefer different rifamycins. The objective of the study was to compare microbial kill and resistance emergence of rifamycins using principles of pharmacokinetics/pharmacodynamics. First, we identified rifamycin MICs in 20 MAC isolates from patients followed by concentration-response studies in test-tubes. Next, we examined efficacy and resistance suppression of three doses of each rifamycin in the hollow fiber system model of pulmonary MAC [HFS-MAC], mimicking human like concentration-time profile of the drugs. HFS-MAC units were repetitively sampled for total and drug-resistant MAC burden and for drug concentration measurements. Inhibitory sigmoid E max model, linear regression, and analysis of variance was used for data analysis. For rifabutin 90% of isolates had MIC ≤ 0.125 mg/L while for both rifampin and rifapentine this was ≤2.0 mg/L. There was no statistically significant difference (p > 0.05) in maximal kill and effective concentration mediating 50% of the bacterial kill among three rifamycins in the static concentration experiment. In the HFS-MAC, the bactericidal kill (day 0-4) for rifampin was 0.89 (95% Confidence Interval (CI): 0.43-1.35), for rifapentine was 1.05 (95% CI: 0.08-1.23), and for rifabutin was 0.92 (95% CI: 0.61-1.24) log10 CFU/ml, respectively. Rifamycins monotherapy failed after just 4-days of treatment and entire MAC population was drug resistant on day 26 of the study. There was no dose dependent difference in MAC kill or resistance suppression among the three rifamycins tested in the HFS-MAC. Therefore, replacing one rifamycin, due to emergence of drug-resistance, with other may not be beneficial in clinical setting.

Therapeutic Drug Monitoring in Non-Tuberculosis Mycobacteria Infections

Nontuberculous mycobacteria can cause minimally symptomatic self-limiting infections to progressive and life-threatening disease of multiple organs. Several factors such as increased testing and prevalence have made this an emerging infectious disease. Multiple guidelines have been published to guide therapy, which remains difficult owing to the complexity of therapy, the potential for acquired resistance, the toxicity of treatment, and a high treatment failure rate. Given the long duration of therapy, complex multi-drug treatment regimens, and the risk of drug toxicity, therapeutic drug monitoring is an excellent method to optimize treatment. However, currently, there is little available guidance on therapeutic drug monitoring for this condition. The aim of this review is to provide information on the pharmacokinetic/pharmacodynamic targets for individual drugs used in the treatment of nontuberculous mycobacteria disease. Lacking data from randomized controlled trials, in vitro, in vivo, and clinical data were aggregated to facilitate recommendations for therapeutic drug monitoring to improve efficacy and reduce toxicity.

Novel therapies for treatment of resistant and refractory nontuberculous mycobacterial infections in patients with cystic fibrosis

Respiratory infections caused by non-tuberculous mycobacteria (NTM) are a major cause of morbidity for patients living with cystic fibrosis (CF), as NTM pulmonary disease (NTM-PD) is challenging to both diagnose and eradicate. Despite the lengthy courses of the established regimens recommended by the Cystic Fibrosis Foundation (CFF) and European Cystic Fibrosis Society (ECFS) consensus guidelines, only about 50% to 60% of patients achieve culture conversion, and treatment regimens are often complicated by antibiotic resistance and toxicities. Since publication of the CFF/ECFS guidelines, several new or alternative antibiotic regimens have been described for patients with CF who have NTM-PD. These regimens offer new options for patients who do not clear NTM with standard therapies or cannot utilize the usual regimens due to toxicities or drug-drug interactions.

Comparison of a Novel Regimen of Rifapentine, Tedizolid, and Minocycline with Standard Regimens for Treatment of Pulmonary Mycobacterium kansasii

The combination of isoniazid, rifampin, and ethambutol is recommended by the American Thoracic Society (ATS) for treatment of pulmonary Mycobacterium kansasii, while the British Thoracic Society (BTS) recommends clarithromycin, rifampin and ethambutol. Unfortunately, therapy duration for both regimens lasts for years. In this study, we administered tedizolid, minocycline, clarithromycin, and rifapentine as monotherapy as well as novel combinations in the intracellular hollow-fiber model system of M. kansasii (HFS-Mkn) in a 28-day study. The ATS and BTS regimens were used as comparators. Repetitive sampling was used to validate the intended intrapulmonary pharmacokinetics of each drug and to monitor changes in M. kansasii burden. As monotherapy, tedizolid at an observed area under the concentration-time curve from 0 to 24 h (AUC_0-24)/MIC of 5.85 and minocycline at an AUC_0-24/MIC of 5.77 failed to kill the bacteria below day 0 (stasis), clarithromycin at an AUC_0-24/MIC of 2.4 held the bacterial burden at stasis, but rifapentine at an AUC_0-24/MIC of 140 killed 2 log₁₀ CFU/ml below stasis. The BTS regimen kill slope was -0.083 ± 0.035 CFU/ml/day, which was significantly superior to the ATS regimen slope of -0.038 ± 0.038 CFU/ml/day. The rifapentine-tedizolid-minocycline combination kill slope was -0.119 ± 0.031 CFU/ml/day, superior to that of the ATS regimen and comparable to that of the BTS regimen. In conclusion, the BTS regimen and the novel rifapentine-tedizolid-minocycline regimen showed better kill of intracellular bacteria in the HFS-Mkn However, the efficacy of the new combination regimen remains to be tested in clinical settings.

Minocycline treatment for pulmonary Mycobacterium avium complex disease based on pharmacokinetics/pharmacodynamics and Bayesian framework mathematical models

OBJECTIVES

Our aim was to identify the pharmacokinetic/pharmacodynamic parameters of minocycline in the hollow-fibre system (HFS) model of pulmonary Mycobacterium avium complex (MAC) and to identify the optimal clinical dose.

METHODS

Minocycline MICs for 55 MAC clinical isolates from the Netherlands were determined. We also co-incubated primary isolated macrophages infected with MAC with minocycline. Next, we performed a 28 day HFS-MAC model dose-response study in which we mimicked pulmonary concentration-time profiles achieved in patients. The HFS-MAC model was sampled at intervals to determine the minocycline pharmacokinetics and MAC burden. We identified the AUC0-24/MIC ratios associated with 1.0 log10 cfu/mL kill below day 0 (stasis), defined as a bactericidal effect. We then performed 10000 Monte Carlo experiments to identify the optimal dose for a bactericidal effect in patients.

RESULTS

The MIC for 50% and 90% of cumulative clinical isolates was 8 and 64 mg/L, respectively. Minocycline decreased MAC bacterial burden below stasis in primary isolated macrophages. In the HFS-MAC model, minocycline achieved a microbial kill of 3.6 log10 cfu/mL below stasis. The AUC0-24/MIC exposure associated with a bactericidal effect was 59. Monte Carlo experiments identified a minocycline susceptibility MIC breakpoint of 16 mg/L. At this proposed breakpoint, the clinical dose of 200 mg/day achieved the bactericidal effect exposure target in ∼50% of patients, while 400 mg/day achieved this in 73.6% of patients, in Monte Carlo experiments.

CONCLUSIONS

Minocycline at a dose of 400 mg/day is expected to be bactericidal. We propose a clinical trial for validation.

Preclinical Models of Nontuberculous Mycobacteria Infection for Early Drug Discovery and Vaccine Research

Nontuberculous mycobacteria (NTM) represent an increasingly prevalent etiology of soft tissue infections in animals and humans. NTM are widely distributed in the environment and while, for the most part, they behave as saprophytic organisms, in certain situations, they can be pathogenic, so much so that the incidence of NTM infections has surpassed that of Mycobacterium tuberculosis in developed countries. As a result, a growing body of the literature has focused attention on the critical role that drug susceptibility tests and infection models play in the design of appropriate therapeutic strategies against NTM diseases. This paper is an overview of the in vitro and in vivo models of NTM infection employed in the preclinical phase for early drug discovery and vaccine development. It summarizes alternative methods, not fully explored, for the characterization of anti-mycobacterial compounds.

The crystal structure of 5-bromo-2-(2-methyl-2H-tetrazol-5-yl)pyridine, C7H6BrN5

C7H6BrN5, triclinic, P1̄ (no. 2), a = 8.3319(4) Å, b = 10.0666(5) Å, c = 11.4042(6) Å, α = 107.213(5)°, β = 99.394(4)°, γ = 95.540(4)°, V = 890.71(8) Å3, Z = 4, R gt(F) = 0.0452, wR ref(F 2) = 0.0972, T = 293(2) K.

Co-existence of the oxazolidinone resistance genes cfr and optrA on two transferable multi-resistance plasmids in one Enterococcus faecalis isolate from swine

OBJECTIVES

To identify and characterize oxazolidinone resistance genes cfr and optrA in enterococcal isolates.

METHODS

Two hundred and ninety-three enterococcal isolates were screened for the presence of cfr and optrA by polymerase chain reaction. The transferability of cfr and optrA was examined by conjugation. S1 nuclease pulsed-field gel electrophoresis and Southern blotting were used to identify the location of cfr and optrA. One Enterococcus faecalis isolate carrying both cfr and optrA was sequenced in full.

RESULTS

cfr and optrA were detected in 16 (5.5%) and 170 (58.0%) enterococcal isolates, respectively. Sixteen enterococcal isolates (E. faecalis n=13, Enterococcus avium n=2, Enterococcus mundtii n=1) carried both cfr and optrA. The cfr-carrying fragment between res and theta in plasmid p4 showed 98.9% identity to the corresponding region of plasmid pEF120805 from vancomycin-resistant Enterococcus faecium. The optrA-carrying segment between tnpB and optrA in plasmid p1 showed >99.9% identity to the corresponding region of genomic DNA from E. faecalis A101. Plasmid p4 and plasmid p1 were simultaneously conjugated to E. faecalis JH2-2.

CONCLUSIONS

One hundred and seventy optrA-positive enterococci were identified in 293 enterococcal isolates from swine and the farm environment. The co-existence of cfr and optrA in E. avium and E. mundtii has been identified previously. cfr and optrA were identified on two new conjugative plasmids from one E. faecalis isolate. The optrA-carrying segment (IS1216E-optrA-IS1216E) was reported initially. Among different types of enterococcal plasmids, ISEnfa5 and IS1216E elements may play a vital role in the dissemination of cfr and optrA, respectively.

Tedizolid phosphate for the treatment of acute bacterial skin and skin-structure infections: an evidence-based review of its place in therapy

Introduction

Tedizolid phosphate is an oxazolidinone approved for the treatment of acute bacterial skin and skin-structure infections (ABSSSIs) and active against methicillin-resistant Staphylococcus aureus.

Aims

The objective of this article was to review the evidence for the efficacy and safety of tedizolid phosphate for the treatment of ABSSSI.

Evidence review

Approval of tedizolid phosphate for the treatment of ABSSSI was based on the results of two phase III randomized controlled trials, ESTABLISH-1 (NCT01170221) and ESTABLISH-2 (NCT01421511), comparing 6-day once-daily tedizolid vs 10-day twice-daily linezolid. In ESTABLISH-1, noninferiority was met with early clinical response rates of 79.5% and 79.4% in tedizolid and linezolid groups, respectively (difference 0.1%, 95% CI –6.1% to 6.2%, with a 10% noninferiority margin). In ESTABLISH-2, noninferiority was met with 85% and 83% rates of early clinical response in tedizolid and linezolid groups, respectively (difference 2.6%, 95% CI –3.0% to 8.2%). Pooled data from ESTABLISH-1 and ESTABLISH-2 indicated a lower frequency of thrombocytopenia in tedizolid-treated than in linezolid-treated patients.

Conclusion

Tedizolid offers the option of an intravenous to oral switch, allows once-daily administration, and presents lower risk of myelotoxicity when a 6-day course is used for the treatment of ABSSSI. Greater economic cost associated with this antibiotic could be offset by its shorter treatment duration and possibility of oral administration in routine clinical practice, although either sponsored or nonsponsored postmarketing observational experience remains essential for ultimately confirming the effectiveness and tolerability of tedizolid outside clinical trials.

Multiparameter Responses to Tedizolid Monotherapy and Moxifloxacin Combination Therapy Models of Children With Intracellular Tuberculosis

Background

Children are often neglected during early development of antituberculosis agents, and most receive treatment after it is first tested in adults. However, very young children have tuberculosis that differs in many respects from adult cavitary pneumonia and could have different toxicity profiles to drugs. Linezolid is effective against intracellular tuberculosis, a common manifestation in young children. However, linezolid has considerable toxicity due to inhibition of mitochondrial enzymes. Tedizolid could be a replacement if it shows equal efficacy and reduced toxicity.

Methods

We performed tedizolid dose-effect studies in the hollow fiber system model of intracellular tuberculosis. We measured linezolid concentrations, colony-forming units (CFU), time-to-positivity, and monocyte viability and performed RNA sequencing on infected cells collected from repetitive sampling of each system. We also compared efficacy of tedizolid vs linezolid and vs tedizolid-moxifloxacin combination.

Results

There was no downregulation of mitochondrial enzyme genes, with a tedizolid 0-24 hour area under the concentration-time curve (AUC0-24) of up to 90 mg*h/L. Instead, high exposures led to increased mitochondrial gene expression and monocyte survival. The AUC0-24 to minimum inhibitory concentration ratio associated with 80% of maximal bacterial kill (EC80) was 184 by CFU/mL (r2 = 0.96) and 189 by time-to-positivity (r2 = 0.99). Tedizolid EC80 killed 4.0 log10 CFU/mL higher than linezolid EC80. The tedizolid-moxifloxacin combination had a bacterial burden elimination rate constant of 0.27 ± 0.05 per day.

Conclusions

Tedizolid demonstrated better efficacy than linezolid, without the mitochondrial toxicity gene or cytotoxicity signatures encountered with linezolid. Tedizolid-moxifloxacin combination had a high bacterial elimination rate.

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.

Linezolid as treatment for pulmonary Mycobacterium avium disease

Objectives

To identify the pharmacokinetic/pharmacodynamic parameters and exposures of linezolid in the treatment of pulmonary Mycobacterium avium complex (MAC) disease.

Methods

Human-derived monocytes infected with MAC were inoculated into hollow-fibre systems for dose-effect and dose-scheduling studies. We mimicked linezolid concentration-time profiles achieved in adult human lungs treated for 28 days. Sampling to confirm that the intended linezolid pharmacokinetics had been achieved, and for enumeration of MAC colony-forming units, was performed based on repetitive sampling from each system over the 28 days. We then performed 10 000 patient Monte Carlo simulations to identify doses associated with optimal effect in the clinic.

Results

Linezolid achieved a hitherto unprecedented feat of at least 1.0 log10 cfu/mL reduction. Efficacy was most closely linked to the AUC0-24/MIC ratio. The AUC0-24/MIC ratio associated with no change in bacterial burden or bacteriostasis was 7.82, while that associated with 1.0 log10 cfu/mL kill was 42.06. The clinical dose of 600 mg/day achieved or exceeded the bacteriostasis exposure in 98.73% of patients. The proportion of 10 000 patients treated with the standard 1200 mg/day who achieved the exposure for 1.0 log10 cfu/mL kill was 70.64%, but was 90% for 1800 mg/day. The proposed MIC breakpoint for linezolid is 16 mg/L, with which 49%-80% of clinical isolates would be considered resistant.

Conclusions

Linezolid is associated with a bactericidal effect in pulmonary MAC that is greater than that seen with other recommended drugs. However, because of the MIC distribution, doses that would optimize the bactericidal effect would be associated with a high adverse event rate.

A programme to create short-course chemotherapy for pulmonary Mycobacterium avium disease based on pharmacokinetics/pharmacodynamics and mathematical forecasting

Objectives

Pulmonary Mycobacterium avium complex (MAC) prevalence is on the rise worldwide. The average therapy duration is 1.5 years, which is associated with poor cure rates. Our objective was to develop a programme to design a combination therapy regimen for pulmonary MAC to be administered for 6 months or less with efficacy in > 90% of patients.

Methods

We performed a literature search for the following MeSH headings 'Mycobacterium avium' AND 'pharmacokinetics/pharmacodynamics' in PubMed up to 2016. The findings were then used to identify steps in the programme to design new regimens with faster microbial kill rates than the current standard regimen.

Results

First, we designed a strategy for rapid in vitro screening of all antibiotic classes for repurposing against pulmonary MAC. Secondly, we identified and compared maximal microbial kill rates (Emax), and optimal exposures of eight different antibiotics. These studies had all been performed in the hollow-fibre system model of pulmonary MAC (HFS-MAC). Thirdly, all drugs with a high Emax at clinically achievable optimal exposures will be chosen, and exposures associated with synergy or additivity for two/three drugs identified based on Bliss independence. Fourthly, the time-kill slopes and resistance suppression of the chosen combinations will be compared with those of standard combination therapy in the HFS-MAC. Finally, we will identify the clinical doses best able to achieve synergistic or additive combination exposures by taking into account pharmacokinetic variability.

Conclusions

Our stepwise pharmacokinetics/pharmacodynamics approach provides a scientific rationale and a strategy for achieving short-course chemotherapy for pulmonary MAC disease within a few years.

A 'shock and awe' thioridazine and moxifloxacin combination-based regimen for pulmonary Mycobacterium avium-intracellulare complex disease

Objectives

To develop a thioridazine/moxifloxacin-based combination regimen for treatment of pulmonary infection due to Mycobacterium avium-intracellulare complex (MAC) that kills bacteria faster than the standard treatment regimen.

Methods

Monocytes were infected with MAC and inoculated into the hollow-fibre system model for pulmonary MAC disease (HFS-MAC). We co-administered ethambutol plus azithromycin daily for 28 days, to achieve the same human concentration-time profiles that result from standard doses, in three HFS-MAC systems. Two experimental regimens consisted of thioridazine at an exposure associated with optimal kill, given intermittently on days 0, 3, 7 and 10. Regimen A consisted of thioridazine in combination with standard dose azithromycin for the entire study duration. Regimen B was thioridazine plus moxifloxacin at concentration-time profiles achieved by the standard daily dose administered for 14 days, followed by daily azithromycin. Each HFS-MAC was sampled for bacterial burden every 7 days.

Results

The bacteria in the non-treated HFS-MAC grew at a rate of 0.11 ± 0.01 log10 cfu/mL/day. The azithromycin/ethambutol regimen decreased bacterial burden by 1.21 ± 0.74 log10 cfu/mL below baseline during the first 7 days, after which it failed. Regimen A killed 3.28 ± 0.32 log10 cfu/mL below baseline up to day 14, after which regrowth occurred once thioridazine treatment stopped. Regimen B killed bacteria to below the limits of detection in 7 days (≥5.0 log10 cfu/mL kill), with rebound in the azithromycin continuation phase.

Conclusions

The thioridazine/moxifloxacin regimen demonstrated that rapid microbial kill could be achieved within 7 days. This is a proof of principle that short-course chemotherapy for pulmonary MAC is possible.

Meta-analyses and the evidence base for microbial outcomes in the treatment of pulmonary Mycobacterium avium-intracellulare complex disease

Objectives

To perform a systematic review and meta-analysis of the level of funding support and the sputum culture conversion rates in pulmonary Mycobacterium avium-intracellulare complex (P-MAC) disease in adult patients without cystic fibrosis or HIV infection, treated with recommended antibiotic regimens.

Methods

We performed a literature search to identify clinical trials, prospective studies and registries that reported outcomes in P-MAC patients. Studies that reported P-MAC diagnosis and treatments based on established guidelines met the inclusion criteria and were examined for bias and quality. We modified existing quality scales and came up with a 10 star quality score. Outcomes meta-analysed were sputum conversion incidence ratios (IR) and their 95% CI, weighted for study quality.

Results

Twenty-one studies that examined 28 regimens, including 2534 patients in intent-to-treat analyses and 1968 in per-protocol analyses, were identified. The study quality mean ± SD scores were 5.4 ± 2.2 out of 10 stars. Only two (9.5%) studies received public funding. There was significant heterogeneity of microbial effect among treatment regimens (I2 > 40%; P > 0.001). The pooled IR for sustained sputum conversion was 0.54 (95% CI 0.45-0.63) for macrolide-containing regimens versus 0.38 (0.25-0.52) with macrolide-free regimens. Prolonging therapy duration beyond 12 months was associated with an average decline in sputum conversion to 22% (95% CI 1%-44%).

Conclusions

Researchers working on P-MAC therapy have received very little public funding support. As a result, the evidence base for treatment guidelines is based on studies of relatively small numbers of patients in low-quality studies. Nevertheless, these studies showed poor sputum conversion rates in patients receiving recommended treatment regimens.

A novel ceftazidime/avibactam, rifabutin, tedizolid and moxifloxacin (CARTM) regimen for pulmonary Mycobacterium avium disease

Objectives

To compare the efficacy of ceftazidime/avibactam plus tedizolid-based combination regimens with the standard therapy of azithromycin, ethambutol and rifabutin for the treatment of pulmonary Mycobacterium avium complex (MAC) disease.

Methods

We mimicked the human pulmonary concentration-time profiles of ceftazidime/avibactam and tedizolid in combination, ceftazidime/avibactam, rifabutin, tedizolid and moxifloxacin (CARTM), and the standard regimen and examined microbial kill in triplicate hollow-fibre system model of intracellular pulmonary MAC (HFS-MAC) units. The tedizolid and moxifloxacin doses used were non-optimized; the tedizolid dose was that associated with bacteriostasis. Drugs were administered daily for 28 days. Each HFS-MAC was sampled in the central and peripheral compartment to ascertain that the intended drug exposures had been achieved. The peripheral compartments were sampled at regular intervals over the 28 days to quantify the burden of MAC.

Results

MAC-infected macrophages in the HFS-MAC achieved multi-fold higher intracellular versus extracellular concentrations of rifabutin, moxifloxacin, ceftazidime/avibactam. The non-optimized ceftazidime/avibactam plus tedizolid dual therapy held the bacterial burden at the same level as day 0 (stasis) throughout the 28 days. The standard therapy reduced the bacterial load 2 log10 cfu/mL below stasis on day 14 but started failing after that. The CARTM regimen achieved 3.2 log10 cfu/mL kill below stasis on day 21, but had started to fail by day 28.

Conclusions

The CARTM regimen promises to have kill rates better than standard therapy. Experiments to identify exposures of each of the four drugs associated with optimal effect in the CARTM combination are needed in order to design a short-course chemotherapy regimen.

The discovery of ceftazidime/avibactam as an anti-Mycobacterium avium agent

OBJECTIVES

To determine if ceftaroline and ceftazidime combined with avibactam are efficacious against pulmonary Mycobacterium avium complex (MAC) disease.

METHODS

First, we performed a concentration-effect study of ceftaroline and ceftaroline/avibactam against extracellular MAC in test tubes. Given the difficulty of obtaining avibactam at the time of experimentation, we used a single concentration of commercial ceftazidime/avibactam, and two sets of non-treated controls, one with ceftazidime/avibactam and the other without. After finding antimicrobial activity with the ceftazidime/avibactam 'control', we performed ceftazidime/avibactam dose-effect studies in test tubes against extracellular MAC and in 24-well plates against intracellular MAC. We then performed a ceftazidime/avibactam exposure-effect and dose-fractionation studies in the hollow-fibre system model of intracellular pulmonary MAC (HFS-MAC). In each experiment, we repetitively sampled each HFS-MAC at specified times to validate ceftazidime/avibactam pharmacokinetics and to quantify bacterial burden.

RESULTS

Ceftaroline killed extracellular MAC with maximal microbial kill (Emax) of 4.87 ± 0.26 log10 cfu/mL. However, the ceftazidime/avibactam 'control' also killed MAC compared with the non-treated control. Ceftazidime/avibactam Emax was 3.8 log10 cfu/mL against extracellular bacilli and 3.6 log10 cfu/mL against intracellular MAC. In the HFS-MAC, ceftazidime/avibactam achieved a half-life of 2.5-3.3 h and killed MAC 0.61-2.40 log10 cfu/mL below the starting bacterial burden. The ceftazidime/avibactam efficacy was linked to the proportion of the dosing interval for which the concentration persists above the MIC (fT>MIC), with optimal efficacy at free-drug fT>MIC of 52% (r2 = 0.95).

CONCLUSIONS

Ceftazidime/avibactam effectively kills MAC at exposures easily achieved in the lung by clinical doses. Efficacy was higher than with clinically achievable doses of azithromycin and ethambutol.