Pharmacokinetics of bedaquiline in cerebrospinal fluid (CSF) in patients with pulmonary tuberculosis (TB)

Role of therapeutic drug monitoring in the treatment of multi-drug resistant tuberculosis

Tuberculosis (TB) is a leading cause of mortality worldwide, and resistance to anti-tuberculosis drugs is a challenge to effective treatment. Multi-drug resistant TB (MDR-TB) can be difficult to treat, requiring long durations of therapy and the use of second line drugs, increasing a patient's risk for toxicities and treatment failure. Given the challenges treating MDR-TB, clinicians can improve the likelihood of successful outcomes by utilizing therapeutic drug monitoring (TDM). TDM is a clinical technique that utilizes measured drug concentrations from the patient to adjust therapy, increasing likelihood of therapeutic drug concentrations while minimizing the risk of toxic drug concentrations. This review paper provides an overview of the TDM process, pharmacokinetic parameters for MDR-TB drugs, and recommendations for dose adjustments following TDM.

Granulomatous amoebic encephalitis due to Acanthamoeba spp complicating multidrug-resistant tuberculous meningitis in an immunocompetent individual

Granulomatous amoebic encephalitis due to Acanthamoeba spp is a rare, near-fatal central nervous system infection. It is often seen in immunocompromised individuals. Here we describe a survivor of this infection who was co-infected with multidrug-resistant tuberculosis. He presented to us with features of meningitis and a history of chronic cough. The chest X-ray was classical for pulmonary tuberculosis. Neuroimaging was suggestive of encephalitis; herpes simplex virus PCR was negative. Cerebrospinal fluid (CSF) showed lymphocytic pleocytosis. Wet mounts revealed trophozoites of Acanthamoeba Currently, he is being treated with oral bedaquiline, levofloxacin, linezolid, clofazimine, cycloserine and pyridoxine for tuberculosis. He received intravenous amikacin and oral cotrimoxazole and fluconazole for Acanthamoeba infection for 1 month. The resolution was confirmed by repeating the CSF wet mount, culture and neuroimaging. He was then discharged with oral rifampicin, cotrimoxazole and fluconazole. He is currently under our close follow-up.

Predictions of Bedaquiline Central Nervous System Exposure in Patients with Tuberculosis Meningitis Using Physiologically based Pharmacokinetic Modeling

BACKGROUND AND OBJECTIVE

The use of bedaquiline as a treatment option for drug-resistant tuberculosis meningitis (TBM) is of interest to address the increased prevalence of resistance to first-line antibiotics. To this end, we describe a whole-body physiologically based pharmacokinetic (PBPK) model for bedaquiline to predict central nervous system (CNS) exposure.

METHODS

A whole-body PBPK model was developed for bedaquiline and its metabolite, M2. The model included compartments for brain and cerebrospinal fluid (CSF). Model predictions were evaluated by comparison to plasma PK time profiles following different dosing regimens and sparse CSF concentrations data from patients. Simulations were then conducted to compare CNS and lung exposures to plasma exposure at clinically relevant dosing schedules.

RESULTS

The model appropriately described the observed plasma and CSF bedaquiline and M2 concentrations from patients with pulmonary tuberculosis (TB). The model predicted a high impact of tissue binding on target site drug concentrations in CNS. Predicted unbound exposures within brain interstitial exposures were comparable with unbound vascular plasma and unbound lung exposures. However, unbound brain intracellular exposures were predicted to be 7% of unbound vascular plasma and unbound lung intracellular exposures.

CONCLUSIONS

The whole-body PBPK model for bedaquiline and M2 predicted unbound concentrations in brain to be significantly lower than the unbound concentrations in the lung at clinically relevant doses. Our findings suggest that bedaquiline may result in relatively inferior efficacy against drug-resistant TBM when compared with efficacy against drug-resistant pulmonary TB.

Comprehensive Therapeutic Approaches to Tuberculous Meningitis: Pharmacokinetics, Combined Dosing, and Advanced Intrathecal Therapies

Tuberculous meningitis (TBM) presents a critical neurologic emergency characterized by high mortality and morbidity rates, necessitating immediate therapeutic intervention, often ahead of definitive microbiological and molecular diagnoses. The primary hurdle in effective TBM treatment is the blood-brain barrier (BBB), which significantly restricts the delivery of anti-tuberculous medications to the central nervous system (CNS), leading to subtherapeutic drug levels and poor treatment outcomes. The standard regimen for initial TBM treatment frequently falls short, followed by adverse side effects, vasculitis, and hydrocephalus, driving the condition toward a refractory state. To overcome this obstacle, intrathecal (IT) sustained release of anti-TB medication emerges as a promising approach. This method enables a steady, uninterrupted, and prolonged release of medication directly into the cerebrospinal fluid (CSF), thus preventing systemic side effects by limiting drug exposure to the rest of the body. Our review diligently investigates the existing literature and treatment methodologies, aiming to highlight their shortcomings. As part of our enhanced strategy for sustained IT anti-TB delivery, we particularly seek to explore the utilization of nanoparticle-infused hydrogels containing isoniazid (INH) and rifampicin (RIF), alongside osmotic pump usage, as innovative treatments for TBM. This comprehensive review delineates an optimized framework for the management of TBM, including an integrated approach that combines pharmacokinetic insights, concomitant drug administration strategies, and the latest advancements in IT and intraventricular (IVT) therapy for CNS infections. By proposing a multifaceted treatment strategy, this analysis aims to enhance the clinical outcomes for TBM patients, highlighting the critical role of targeted drug delivery in overcoming the formidable challenges presented by the blood-brain barrier and the complex pathophysiology of TBM.

Advancing Diagnosis and Treatment in People Living with HIV and Tuberculosis Meningitis

PURPOSE OF REVIEW

Tuberculous meningitis (TBM) is the most severe form of tuberculosis. Inadequate diagnostic testing and treatment regimens adapted from pulmonary tuberculosis without consideration of the unique nature of TBM are among the potential drivers. This review focuses on the progress being made in relation to both diagnosis and treatment of TBM, emphasizing promising future directions.

RECENT FINDINGS

The molecular assay GeneXpert MTB/Rif Ultra has improved sensitivity but has inadequate negative predictive value to "rule-out" TBM. Evaluations of tests focused on the host response and bacterial components are ongoing. Clinical trials are in progress to explore the roles of rifampin, fluoroquinolones, linezolid, and adjunctive aspirin. Though diagnosis has improved, novel modalities are being explored to improve the rapid diagnosis of TBM. Multiple ongoing clinical trials may change current therapies for TBM in the near future.

Current Insights into Diagnosing and Treating Neurotuberculosis in Adults

Neurotuberculosis has the highest morbidity and mortality risk of all forms of extrapulmonary tuberculosis (TB). Early treatment is paramount, but establishing diagnosis are challenging in all three forms of neurotuberculosis: tuberculous meningitis (TBM), spinal TB and tuberculomas. Despite advancements in diagnostic tools and ongoing research aimed at improving TB treatment regimens, the mortality rate for neurotuberculosis remains high. While antituberculosis drugs were discovered in the 1940s, TB treatment regimens were designed for and studied in pulmonary TB and remained largely unchanged for decades. However, new antibiotic regimens and host-directed therapies are now being studied to combat drug resistance and contribute to ending the TB epidemic. Clinical trials are necessary to assess the effectiveness and safety of these treatments, addressing paradoxical responses in neurotuberculosis cases and ultimately improving patient outcomes. Pharmacokinetic-pharmacodynamic analyses can inform evidence-based dose selection and exposure optimization. This review provides an update on the diagnosis and treatment of neurotuberculosis, encompassing both sensitive and resistant antituberculosis drug approaches, drawing on evidence from the literature published over the past decade.

Liquid chromatography-tandem mass spectrometry analysis of delamanid and its metabolite in human cerebrospinal fluid using protein precipitation and on-line solid-phase extraction

The penetration of the antituberculosis drug delamanid into the central nervous system is not established. The distribution of delamanid and its major metabolite, DM-6705, into the cerebrospinal fluid requires investigation. A liquid chromatography-tandem mass spectrometry method for the quantification of delamanid and DM-6705 in human cerebrospinal fluid was developed and validated. The calibration range for both analytes was 0.300 - 30.0 ng/mL. The deuterium-labelled analogue of delamanid (delamanid-d4) and OPC-14714 were used as internal standards for delamanid and DM-6705, respectively. Samples were processed by protein precipitation followed by on-line solid-phase extraction and high-performance liquid chromatography on an Agilent 1260 HPLC system. A Phenomenex Gemini-NX C18 (5.0 µm, 50 mm × 2.0 mm) analytical column was used for on-line solid-phase extraction, and a Waters Xterra MS C18 (5.0 µm, 100 mm × 2.1 mm) analytical column for chromatographic separation using gradient elution, at a flow rate of 300 µL/min. The total run time was 7.5 min. Analytes were detected by multiple reaction monitoring on an AB Sciex 5500 triple quadrupole mass spectrometer at unit mass resolution, with electrospray ionization in the positive mode. Accuracy and precision were assessed over three independent validation batches. Extraction recoveries were more than 98% and were consistent across the analytical range. Both analytes in CSF exhibited non-specific adsorption to polypropylene tubes. The method was used to analyse cerebrospinal fluid samples from patients with pulmonary tuberculosis in an exploratory pharmacokinetic study.

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

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

Pharmacokinetics of Antituberculosis Drugs in Plasma and Cerebrospinal Fluid in a Patient with Pre-Extensive Drug Resistant Tuberculosis Meningitis

Drug-resistant tuberculous meningitis (TBM) is the most devastating and critical form of extrapulmonary tuberculosis. Here, we present a case of a 45-year-old male with pre-extensive drug-resistant tuberculosis meningitis (pre-XDR-TBM). He underwent emergency surgery for the long-tunneled external ventricular drainage (LTEVD). Molecular test and phenotypic drug sensitivity test (DST) of Mycobacterium tuberculosis in cerebrospinal fluid (CSF) showed that the isolate was resistant to both rifampin and fluoroquinolones. An anti-tuberculous regimen of isoniazid, pyrazinamide, cycloserine, moxifloxacin, clofazimine, and linezolid was tailored accordingly. We monitored the drug concentration in his plasma and CSF before (at 0-hour) and after anti-TB drugs administration (at 1-hour, 2-hour, 6-hour, and 12-hour) on 10^th day after treatment initiation. We hope to provide reference values of drug exposures in plasma and CSF for patients with pre-XDR-TBM.

Dynamic 18F-Pretomanid PET imaging in animal models of TB meningitis and human studies

Pretomanid is a nitroimidazole antimicrobial active against drug-resistant Mycobacterium tuberculosis and approved in combination with bedaquiline and linezolid (BPaL) to treat multidrug-resistant (MDR) pulmonary tuberculosis (TB). However, the penetration of these antibiotics into the central nervous system (CNS), and the efficacy of the BPaL regimen for TB meningitis, are not well established. Importantly, there is a lack of efficacious treatments for TB meningitis due to MDR strains, resulting in high mortality. We have developed new methods to synthesize ¹⁸F-pretomanid (chemically identical to the antibiotic) and performed cross-species positron emission tomography (PET) imaging to noninvasively measure pretomanid concentration-time profiles. Dynamic PET in mouse and rabbit models of TB meningitis demonstrates excellent CNS penetration of pretomanid but cerebrospinal fluid (CSF) levels does not correlate with those in the brain parenchyma. The bactericidal activity of the BPaL regimen in the mouse model of TB meningitis is substantially inferior to the standard TB regimen, likely due to restricted penetration of bedaquiline and linezolid into the brain parenchyma. Finally, first-in-human dynamic ¹⁸F-pretomanid PET in six healthy volunteers demonstrates excellent CNS penetration of pretomanid, with significantly higher levels in the brain parenchyma than in CSF. These data have important implications for developing new antibiotic treatments for TB meningitis.

Pharmacokinetics of Antimicrobials in Children with Emphasis on Challenges Faced by Low and Middle Income Countries, a Clinical Review

Effective antimicrobial exposure is essential to treat infections and prevent antimicrobial resistance, both being major public health problems in low and middle income countries (LMIC). Delivery of drug concentrations to the target site is governed by dose and pharmacokinetic processes (absorption, distribution, metabolism and excretion). However, specific data on the pharmacokinetics of antimicrobials in children living in LMIC settings are scarce. Additionally, there are significant logistical constraints to therapeutic drug monitoring that further emphasize the importance of understanding pharmacokinetics and dosing in LMIC. Both malnutrition and diarrheal disease reduce the extent of enteral absorption. Multiple antiretrovirals and antimycobacterial agents, commonly used by children in low resource settings, have potential interactions with other antimicrobials. Hypoalbuminemia, which may be the result of malnutrition, nephrotic syndrome or liver failure, increases the unbound concentrations of protein bound drugs that may therefore be eliminated faster. Kidney function develops rapidly during the first years of life and different inflammatory processes commonly augment renal clearance in febrile children, potentially resulting in subtherapeutic drug concentrations if doses are not adapted. Using a narrative review approach, we outline the effects of growth, maturation and comorbidities on maturational and disease specific effects on pharmacokinetics in children in LMIC.

Combination Therapy to Kill Mycobacterium tuberculosis in Its Nonreplicating Persister Phenotype

Mycobacterium tuberculosis (Mtb) exists in various metabolic states, including a nonreplicating persister (NRP) phenotype which may affect response to therapy. We have adopted a model-informed strategy to accelerate discovery of effective Mtb treatment regimens and previously found pretomanid (PMD), moxifloxacin (MXF), and bedaquiline (BDQ) to readily kill logarithmic- and acid-phase Mtb. Here, we studied multiple concentrations of each drug in flask-based, time-kill studies against NRP Mtb in single-, two- and three-drug combinations, including the active M2 metabolite of BDQ. We used nonparametric population algorithms in the Pmetrics package for R to model the data and to simulate the 95% confidence interval of bacterial population decline due to the two-drug combination regimen of PMD + MXF and compared this to observed declines with three-drug regimens. PMD + MXF at concentrations equivalent to average or peak human concentrations effectively eradicated Mtb. Unlike other states for Mtb, we observed no sustained emergence of less susceptible isolates for any regimen. The addition of BDQ as a third drug significantly (P < 0.05) shortened time to total bacterial suppression by 3 days compared to the two-drug regimen, similar to our findings for Mtb in logarithmic or acid growth phases.