Low Antituberculosis Drug Concentrations in HIV-Tuberculosis-Coinfected Adults with Low Body Weight: Is It Time To Update Dosing Guidelines?

Pharmacokinetics of ethambutol and weight banded dosing in South African adults newly diagnosed with tuberculosis and HIV

Ethambutol is used to treat tuberculosis (TB) in individuals living with HIV. Low concentrations of ethambutol have been reported in patients dosed with the World Health Organization (WHO)-recommended first-line regimen. We analyzed the pharmacokinetics of ethambutol in 61 HIV-positive individuals diagnosed with drug-sensitive TB enrolled in the tuberculosis and highly active antiretroviral therapy (TB-HAART) study. Participants started on TB treatment and were randomized to early or later introduction of efavirenz-based antiretroviral treatment. We explored potential covariate effects and evaluated the current WHO dosing recommendations for ethambutol in drug-susceptible and multidrug-resistant (MDR)-TB. A two-compartment model with first-order elimination allometrically scaled by fat-free mass and transit compartment absorption best described the pharmacokinetics of ethambutol. Clearance was estimated to be 40.3 L/h for a typical individual with a fat-free mass (FFM) of 42 kg. The Antib-4 formulation had 26% higher bioavailability and slower mean transit time by 37% compared with Rifafour. Simulations showed that individuals in the lower weight bands (<55 kg) who were administered ethambutol at WHO-recommended doses had relatively low drug exposures. These individuals would need doses of 825 mg if their body weight is <37.9 kg and 1,100 mg if it is between 38 and 54.9 kg to achieve the reference maximum concentrations of 2-6 mg/L and an area under the concentration-time curve (0-24) of 16-29 mg·h/L. To achieve these targets in MDR-TB treatment, a dose increment of 400 mg (extra tablet) would be required for individuals in the lower weight band (<46 kg). Our dose adjustments are consistent with the literature and can be recommended for consideration by the WHO for first-line drug-susceptible and MDR-TB treatment.

Clinical predictors of 3-month isoniazid rifapentine (3HP)-related adverse drug reactions (ADR) during tuberculosis preventive therapy (PAnDoRA-3HP study): an observational study protocol

INTRODUCTION

Tuberculosis (TB) is the leading infectious cause of death globally. Despite WHO recommendations for TB preventive therapy (TPT), challenges persist, including incompletion of treatment and adverse drug reactions (ADRs). There is limited data on the 3-month isoniazid and rifapentine (3HP) pharmacokinetics, pharmacogenomics and their relation with ADRs. Our study aims to describe the pharmacokinetic and pharmacogenomics of 3HP used for TPT, the ADRs and their association with completion rates, and TPT outcomes, providing vital insights for TB control strategies in resource-limited settings.

METHODS

This is an observational cohort study with a nested case-control study. We enrolled consecutive patients who had been initiated on TPT using the 3HP regimen. These are followed up biweekly and then monthly during the active phase of treatment and 3 monthly for 2 years following completion of TPT. ADR evaluation includes clinical assessment and liver function tests. Cases are selected from those who experience ADRs and controls from those who do not. Serum isoniazid and rifapentine concentrations are measured and pharmacogenomic analysis for NAT2, AADAC and CYP2E1 polymorphisms are done. Participants are followed up for 2 years to determine TPT outcomes.

ANALYSIS

The safety profile of 3HP will be assessed using descriptive statistics, including proportions of patients experiencing ADRs and grade 3 or above events related to treatment. χ2 tests and regression models will determine predictors of ADRs and their impact on treatment completion. Pharmacokinetic-pharmacodynamic modelling will establish population parameters and factors influencing rifapentine and isoniazid concentrations.

ETHICS AND DISSEMINATION

Ethical approval of this study inclusive of all the appropriate documents was obtained from the Infectious Diseases Institute Research and Ethics Committee and the Uganda National Council of Science and Technology. The study adheres to legal, ethical and Good Clinical Practice (GCP) guidelines. Deidentified genotype data from 300 patients will be shared after publication. The protocol and phenotype data will be publicly accessible. Abstracts will be submitted to conferences, and a manuscript will be published poststudy.

Progress in Pharmacometrics Implementation and Regulatory Integration in Africa: A Systematic Review

The availability of clinical trial data, advocacy, and increased funding has facilitated the implementation of pharmacometrics in Africa, resulting in the establishment of additional training programs for pharmacometricians. This study conducted a systematic review to evaluate the progress made from the implementation of pharmacometrics in clinical drug development and its adoption into drug approval by regulatory authorities in Africa. We performed a comprehensive literature search using major databases such as PubMed and Google Scholar. The study included articles published until 2024, with no lower cutoff. Articles were excluded if not addressing the research question or of pharmacometrics studies done outside Africa with no collaboration with African researchers (study setting). For the review, a total of 121 articles were included for analysis. Among the reported pharmacometrics approaches, Population pharmacokinetics modeling approaches are the most used (95 (78.5%)). South Africa and Uganda researchers have the most research output in pharmacometrics in Africa (82 (89.1%) and 7 (7.61%), respectively), with the University of Cape Town (South Africa) producing the highest (71 (78.8%)) of all article in Africa. The most studied conditions are TB (43 (35.5%)), HIV (33 (27.3%), TB and HIV (22 (18.2%)), and malaria (12 (9.92%). Pharmacometrics is gaining momentum in Africa, and the progress made since inception will significantly improve the safety and efficacy of therapeutic agents used to treat HIV, TB, and other emerging conditions.

Precision Medicine Strategies to Improve Isoniazid Therapy in Patients with Tuberculosis

Due to interindividual variability in drug metabolism and pharmacokinetics, traditional isoniazid fixed-dose regimens may lead to suboptimal or toxic isoniazid concentrations in the plasma of patients with tuberculosis, contributing to adverse drug reactions, therapeutic failure, or the development of drug resistance. Achieving precision therapy for isoniazid requires a multifaceted approach that could integrate various clinical and genomic factors to tailor the isoniazid dose to individual patient characteristics. This includes leveraging molecular diagnostics to perform the comprehensive profiling of host pharmacogenomics to determine how it affects isoniazid metabolism, such as its metabolism by N-acetyltransferase 2 (NAT2), and studying drug-resistant mutations in the Mycobacterium tuberculosis genome for enabling targeted therapy selection. Several other molecular signatures identified from the host pharmacogenomics as well as other omics-based approaches such as gut microbiome, epigenomic, proteomic, metabolomic, and lipidomic approaches have provided mechanistic explanations for isoniazid pharmacokinetic variability and/or adverse drug reactions and thereby may facilitate precision therapy of isoniazid, though further validations in larger and diverse populations with tuberculosis are required for clinical applications. Therapeutic drug monitoring and population pharmacokinetic approaches allow for the adjustment of isoniazid dosages based on patient-specific pharmacokinetic profiles, optimizing drug exposure while minimizing toxicity and the risk of resistance. Current evidence has shown that with the integration of the host pharmacogenomics-particularly NAT2 and Mycobacterium tuberculosis genomics data along with isoniazid pharmacokinetic concentrations in the blood and patient factors such as anthropometric measurements, comorbidities, and type and timing of food administered-precision therapy approaches in isoniazid therapy can be tailored to the specific characteristics of both the host and the pathogen for improving tuberculosis treatment outcomes.

Assessment of body mass-related covariates for rifampicin pharmacokinetics in healthy Caucasian volunteers

PURPOSE

Currently, body weight-based dosing of rifampicin is recommended. But lately, fat-free mass (FFM) was reported to be superior to body weight (BW). The present evaluation aimed to assess the influence of body mass-related covariates on rifampicin's pharmacokinetics (PK) parameters in more detail using non-linear mixed effects modeling (NLMEM).

METHODS

Twenty-four healthy Caucasian volunteers were enrolled in a bioequivalence study, each receiving a test and a reference tablet of 600 mg of rifampicin separated by a wash-out period of at least 9 days. Monolix version 2023R1 was used for NLMEM. Monte Carlo simulations (MCS) were performed to visualize the relationship of body size descriptors to the exposure to rifampicin.

RESULTS

A one-compartment model with nonlinear (Michaelis-Menten) elimination and zero-order absorption kinetics with a lag time best described the data. The covariate model including fat-free mass (FFM) on volume of distribution (V/F) and on maximum elimination rate (Vmax/F) lowered the objective function value (OFV) by 56.4. The second-best covariate model of sex on V/F and Vmax/F and BW on V/F reduced the OFV by 51.2. The decrease in unexplained inter-individual variability on Vmax/F in both covariate models was similar. For a given dose, MCS showed lower exposure to rifampicin with higher FFM and accordingly in males compared to females with the same BW and body height.

CONCLUSION

Our results indicate that beyond BW, body composition as reflected by FFM could also be relevant for optimized dosing of rifampicin. This assumption needs to be studied further in patients treated with rifampicin.

Clinical Predictors of 3-Months Isoniazid Rifapentine (3HP) - Related Adverse Drug Reactions (ADR) During Tuberculosis Preventive Therapy. (PAnDoRA-3HP study): An Observational Study Protocol

Introduction

Tuberculosis (TB) is the leading infectious cause of death globally. Despite WHO recommendations for Tuberculosis Preventive Therapy (TPT), challenges persist, including incompletion of treatment and adverse drug reactions (ADRs). There is limited data on the 3-month isoniazid and rifapentine (3HP) pharmacokinetics, pharmacogenomics and their relation with ADRs. Our study aims to describe the pharmacokinetic and pharmacogenomics of 3HP used for TPT, the ADRs and their association with completion rates, and TPT outcomes, providing vital insights for TB control strategies in resource-limited settings.

Methods

This is an observational cohort study with a nested case-control study. We enrolled consecutive patients initiated on TPT using the 3HP regimen. These are followed up bi-weekly and then monthly during the active phase of treatment and 3 monthly for 2 years following completion of TPT. ADR evaluation includes clinical assessment and liver function tests. Cases are selected from those who experience ADRs, and controls from those who do not. Serum isoniazid and rifapentine concentrations are measured and pharmacogenomic analysis for NAT2 and CYP2E1 polymorphisms are done. Participants are followed up for 2 years to determine TPT outcomes.

Analysis

The safety profile of 3HP will be assessed using descriptive statistics, including proportions of patients experiencing ADRs and grade 3 or above events related to treatment. Chi-square tests and regression models will determine predictors of ADRs and their impact on treatment completion. Pharmacokinetic-pharmacodynamic modeling will establish population parameters and factors influencing rifapentine and isoniazid concentrations.

Unexpectedly low drug exposures among Ugandan patients with TB and HIV receiving high-dose rifampicin

We characterized the pharmacokinetics of standard- and high-dose rifampicin in Ugandan adults with tuberculosis and HIV taking dolutegravir- or efavirenz-based antiretroviral therapy. A liver model with saturable hepatic extraction adequately described the data, and the increase in exposure between high and standard doses was 4.7-fold. This was lower than what previous reports of dose-exposure nonlinearity would predict and was ascribed to 38% lower bioavailability of the rifampicin-only top-up formulation compared to the fixed-dose combination.

Pharmacogenetic variability and the probability of site of action target attainment during tuberculosis meningitis treatment: A physiologically based pharmacokinetic modeling and simulations study

OBJECTIVE AND METHODS

Our objective was to investigate the role of patient pharmacogenetic variability in determining site of action target attainment during tuberculous meningitis (TBM) treatment. Rifampin and isoniazid PBPK model that included SLCO1B1 and NAT2 effects on exposures respectively were obtained from literature, modified, and validated using available cerebrospinal-fluid (CSF) concentrations. Population simulations of isoniazid and rifampin concentrations in brain interstitial fluid and probability of target attainment according to genotypes and M. tuberculosis MIC levels, under standard and intensified dosing, were conducted.

RESULTS

The rifampin and isoniazid model predicted steady-state drug concentration within brain interstitial fluid matched with the observed CSF concentrations. At MIC level of 0.25 mg/L, 57% and 23% of the patients with wild type and heterozygous SLCO1B1 genotype respectively attained the target in CNS with rifampin standard dosing, improving to 98% and 91% respectively with 35 mg/kg dosing. At MIC level of 0.25 mg/L, 33% of fast acetylators attained the target in CNS with isoniazid standard dosing, improving to 90% with 7.5 mg/kg dosing.

CONCLUSION

In this study, the combined effects of pharmacogenetic and M. tuberculosis MIC variability were potent determinants of target attainment in CNS. The potential for genotype-guided dosing during TBM treatment should be further explored in prospective clinical studies.

Challenges in treating tuberculosis in the elderly population in tertiary institute

Tuberculosis (TB) epidemic is most prevalent in the India with increase in mortality and morbidity. Ongoing elderly population as a result of increase in health care facilities are at high risk of TB. Elderly people are four-fold more prone to TB. Most cases of TB in the elderly result from reactivation of latent TB due to immunosenescence. Major challenge in dealing with therapeutic aspects of elderly patients is recognising frailty to prevent loss of independence. Challenges facing with elderly TB are difficult to reach out to hospital because of poor health seeking behaviour especially elderly female either due to ignorance or neglected by the family members, atypical presentation mimicking other disorders leading to diagnostic delay, if at all diagnosed impoverished tolerance and adherence to treatment due to various factors like associated comorbidities leading to pill load, impaired renal and hepatic functions with aging and stigma. Emerging resistance with usage of non-standard treatment regimens lead to unpropitious outcomes and increases mortality. The mortality rate is six times higher in elderly compared to younger individuals. Hence elderly people need tertiary level health care facilities for enhancing the diagnosis and appropriate management of tuberculosis and its complications. New set of guidelines to be made for elderly to increase adherence and tolerance thereby decreasing drug interactions and adverse drug reactions. With the increased prevalence of TB in the elderly, it is the need of the hour for India, to focus on this vulnerable population as they are a potential source of infection in the community. Awareness to be created among the elderly community regarding this deadly disease and its outcomes to increase their health consciousness and medical attention. Priming the special focus on females coterie as they are the most neglected population in our society.

A narrative review of tuberculosis in the United States among persons aged 65 years and older

Tuberculosis (TB) is a preventable infectious disease that confers significant morbidity, mortality, and psychosocial challenges. As TB incidence in the United States (U.S.) decreased from 9.7/100,000 to 2.2/100,000 from 1993 to 2020, the proportion of cases occurring among adults aged 65 and older increased. We conducted a review of published literature in the U.S. and other similar low-TB-burden settings to characterize the epidemiology and unique diagnostic challenges of TB in older adults. This narrative review also provides an overview of treatment characteristics, outcomes, and research gaps in this patient population. Older adults had a 30% higher likelihood of delayed TB diagnosis, with contributing factors such as acid-fast bacilli sputum smear-negative disease (56%) and non-classical clinical presentation. At least 90% of TB cases among older adults resulted from reactivation of latent TB infection (LTBI), but guidance around when to screen and treat LTBI in these patients is lacking. In addition, routine TB testing methods such as interferon-gamma release assays were two times more likely to have false-negative results among older adults. Advanced age was also often accompanied by complex comorbidities and impaired drug metabolism, increasing the risk of treatment failure (23%) and death (19%). A greater understanding of the unique factors of TB among older adults will inform clinical and public health efforts to improve outcomes in this complex patient population and TB control in the U.S.

Influence of N-acetyltransferase 2 (NAT2) genotype/single nucleotide polymorphisms on clearance of isoniazid in tuberculosis patients: a systematic review of population pharmacokinetic models

Purpose

Significant pharmacokinetic variabilities have been reported for isoniazid across various populations. We aimed to summarize population pharmacokinetic studies of isoniazid in tuberculosis (TB) patients with a specific focus on the influence of N-acetyltransferase 2 (NAT2) genotype/single-nucleotide polymorphism (SNP) on clearance of isoniazid.

Methods

A systematic search was conducted in PubMed and Embase for articles published in the English language from inception till February 2022 to identify population pharmacokinetic (PopPK) studies of isoniazid. Studies were included if patient population had TB and received isoniazid therapy, non-linear mixed effects modelling, and parametric approach was used for building isoniazid PopPK model and NAT2 genotype/SNP was tested as a covariate for model development.

Results

A total of 12 articles were identified from PubMed, Embase, and hand searching of articles. Isoniazid disposition was described using a two-compartment model with first-order absorption and linear elimination in most of the studies. Significant covariates influencing the pharmacokinetics of isoniazid were NAT2 genotype, body weight, lean body weight, body mass index, fat-free mass, efavirenz, formulation, CD4 cell count, and gender. Majority of studies conducted in adult TB population have reported a twofold or threefold increase in isoniazid clearance for NAT2 rapid acetylators compared to slow acetylators.

Conclusion

The variability in disposition of isoniazid can be majorly attributed to NAT2 genotype. This results in a trimodal clearance pattern with a multi-fold increase in clearance of NAT2 rapid acetylators compared to slow acetylators. Further studies exploring the generalizability/adaptability of developed PopPK models in different clinical settings are required.

Standard versus high dose of rifampicin in the treatment of pulmonary tuberculosis: a systematic review and meta-analysis

OBJECTIVES

A growing amount of evidence suggests that the rifampicin dosing currently recommended for tuberculosis treatment could be associated with inadequate exposure and unfavourable outcomes. We aimed to compare clinical and microbiological efficacy and safety outcomes of standard and higher rifampicin dosing.

METHODS

Data sources were MEDLINE, Google Scholar and the Cochrane Library. This was a systematic review and meta-analysis that included experimental or observational studies comparing 8-week sputum culture conversion, treatment failure, or safety outcomes in naïve patients with pulmonary tuberculosis treated with standard (10 mg/kg) or higher doses of rifampicin.

RESULTS

Of a total of 9683 citations screened, eight randomized controlled trials were included, accounting for 1897 subjects; the risk of bias was low in three studies, high in two and intermediate in three. At week 8 a higher proportion of patients in the high-dose group obtained a sputum culture conversion than those in the standard dose group (83.7% versus 80.6%, RR 1.06; 95%CI 1.01-1.12, p 0.028); this result was confirmed in the sub-analysis including patients treated with a rifampicin dose of ≥20 mg/kg, but not in those treated with 11-19 mg/kg. Events of treatment failure at end of treatment showed no significant difference between the two groups (RR 0.84; 95%CI 0.59-1.21, p 0.362). In the analysis evaluating safety outcome, the difference in the occurrence of a grade 3 or 4 liver toxicity or adverse drug reactions leading to discontinuation was not significant at the statistical analysis among the groups (7.2% versus 5.4%, RR 1.19; 95%CI 0.81-1.73, p 0.370, and 1.5% versus 0.6%, RR 2.31; 95%CI 0.65-8.21, p 0.195, respectively). No statistical heterogeneity among studies was observed for each outcome.

CONCLUSIONS

High doses of rifampicin were associated with an increased rate of sputum culture conversion at 8 weeks of treatment, particularly in patients receiving ≥20 mg/kg.

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.

Rifampicin and Isoniazid Maximal Concentrations are Below Efficacy-associated Thresholds in the Majority of Patients: Time to Increase the Doses?

BACKGROUND

The treatment of drug-sensitive tuberculosis (TB) is highly effective; however, many patients have suboptimal drug exposure, which possibly explains treatment failures and selection of resistance. This study aimed to describe the prevalence and determinants of suboptimal maximal concentrations (C_max) for anti-TB drugs.

METHODS

An observational study was conducted in patients receiving first-line anti-TB treatment. At two early time points (T1 and T2), blood samples were withdrawn 2 hours post-dose (C_max) and drug concentrations were measured. Data were expressed as medians (interquartile ranges).

RESULTS

The study included 199 participants: 72.9% were male and the median age was 39.8 years (27.5-51.4). The median C_max at T1 and T2 were 7950 ng/mL and 7122 ng/mL (rifampicin), 3260 ng/mL and 3185 ng/mL (isoniazid), 4210 ng/mL and 5742 ng/mL (ethambutol), and 31 008 ng/mL and 30 352 ng/mL (pyrazinamide), respectively. Higher doses/kg and other variables (being born in Italy and female gender for rifampicin, older age and proton pump inhibitor use for isoniazid, female gender and older age for pyrazinamide) were identified by multivariate linear regression analysis. Participants with a higher body mass index received lower doses/kg of all anti-TB drugs. Suboptimal C_max at T1 and T2 were observed in 60% and 66% (rifampicin), 54% and 55% (isoniazid), 33% and 39% (ethambutol), 20% and 11% (pyrazinamide) of patients. Despite 21% of patients at T1 and 24% at T2 showing two or more drugs with suboptimal exposure, no effect on treatment outcome was observed.

DISCUSSION

The majority of patients receiving first-line anti-TB drugs had low isoniazid and rifampin C_max. Increased doses or the use of therapeutic drug monitoring in selected patients may be advised.