Dose-escalation study of isoniazid in healthy volunteers with the rapid acetylator genotype of arylamine N-acetyltransferase 2

Risk adjustment model for tuberculosis compared to non-tuberculosis mycobacterium or latent tuberculosis infection: Center for Personalized Precision Medicine of Tuberculosis (cPMTb) cohort database

BACKGROUND

The Center for Personalized Precision Medicine of Tuberculosis (cPMTb) was constructed to develop personalized pharmacotherapeutic systems for tuberculosis (TB). This study aimed to introduce the cPMTb cohort and compare the distinct characteristics of patients with TB, non-tuberculosis mycobacterium (NTM) infection, or latent TB infection (LTBI). We also determined the prevalence and specific traits of polymorphisms in N-acetyltransferase-2 (NAT2) and solute carrier organic anion transporter family member 1B1 (SLCO1B1) phenotypes using this prospective multinational cohort.

METHODS

Until August 2021, 964, 167, and 95 patients with TB, NTM infection, and LTBI, respectively, were included. Clinical, laboratory, and radiographic data were collected. NAT2 and SLCO1B1 phenotypes were classified by genomic DNA analysis.

RESULTS

Patients with TB were older, had lower body mass index (BMI), higher diabetes rate, and higher male proportion than patients with LTBI. Patients with NTM infection were older, had lower BMI, lower diabetes rate, higher previous TB history, and higher female proportion than patients with TB. Patients with TB had the lowest albumin levels, and the prevalence of the rapid, intermediate, and slow/ultra-slow acetylator phenotypes were 39.2%, 48.1%, and 12.7%, respectively. The prevalence of rapid, intermediate, and slow/ultra-slow acetylator phenotypes were 42.0%, 44.6%, and 13.3% for NTM infection, and 42.5%, 48.3%, and 9.1% for LTBI, respectively, which did not differ significantly from TB. The prevalence of the normal, intermediate, and lower transporter SLCO1B1 phenotypes in TB, NTM, and LTBI did not differ significantly; 74.9%, 22.7%, and 2.4% in TB; 72.0%, 26.1%, and 1.9% in NTM; and 80.7%, 19.3%, and 0% in LTBI, respectively.

CONCLUSIONS

Understanding disease characteristics and identifying pharmacokinetic traits are fundamental steps in optimizing treatment. Further longitudinal data are required for personalized precision medicine.

TRIAL REGISTRATION

This study registered ClinicalTrials.gov NO. NCT05280886.

Application of a physiologically based pharmacokinetic model to predict isoniazid disposition during pregnancy

Pregnancy can increase the risk of latent tuberculosis infection (LTBI) progression to tuberculosis (TB) disease. Isoniazid (INH) is the preferred preventative treatment for LTBI in pregnancy. INH is mainly cleared by N-acetyltransferase 2 (NAT2) but the pharmacokinetics (PK) of INH in different NAT2 phenotypes during pregnancy is not well characterized. To address this knowledge gap, we used physiologically based pharmacokinetic (PBPK) modeling to evaluate NAT2 phenotype-specific effects of pregnancy on INH disposition. A whole-body PBPK model for INH was developed and verified for non-pregnant NAT2 fast (FA), intermediate (IA), and slow (SA) acetylators. Model predictive performance was assessed using a drug-specific model acceptance criterion for mean plasma area under the curve (AUC) and peak plasma concentration (Cmax ), and the absolute average fold error (AAFE) for individual plasma concentrations. The verified model was extended to simulate INH disposition during pregnancy in NAT2 SA, IA, and FA populations. A sensitivity analysis was conducted using the verified PBPK model and known changes in INH disposition during pregnancy to determine whether NAT2 activity changes during pregnancy or other INH clearance pathways are altered. This analysis suggested that NAT2 activity is unchanged while other INH clearance pathways increase by ~80% during pregnancy. The model was applied to explore the effect of pregnancy on INH disposition in two ethnic populations with different NAT2 phenotype distributions and with high TB burden. Our PBPK model can be used to predict INH disposition during pregnancy in diverse populations and expanded to other drugs cleared by NAT2 during pregnancy.

The role of arylamine N-acetyltransferases in chronic degenerative diseases: Their possible function in the immune system

Since their discovery, arylamine N-acetyltransferases 1 and 2 (NAT1 and NAT2, respectively) have been associated with the metabolism of xenobiotics. NAT2 is the main factor in the therapeutic success of tuberculosis treatment due to its role in the biotransformation of isoniazid. However, researchers have started to investigate the possible participation of NAT1 and NAT2 (NATs) in carcinogenesis, although the mechanisms have not been elucidated fully. NATs enzymatic activity is essential in some types of cancer, such as breast cancer and acute lymphoblastic leukemia. Whether NAT1 and/or NAT2 participate in insulin resistance level in diabetes mellitus or in the immune system remains to be explored. Therefore, it is clear that its role in cell physiology has more implications than just metabolizing compounds.

Economic Evaluation of Multiple-Pharmacogenes Testing for the Prevention of Adverse Drug Reactions in People Living with HIV

Purpose

Pharmacogenetics (PGx) testing is one of the methods for determining whether individuals are at risk of adverse drug reactions (ADRs). It has been reported that multiple-PGx testing, a sequencing technology, has a higher predictive value than single-PGx testing. Therefore, this study aimed to determine the most cost-effective PGx testing strategies for preventing drug-induced serious ADRs in human immunodeficiency virus (HIV)-infected patients.

Patients and Methods

Potential strategies, including 1) single-PGx esting (ie, HLA-B*57:01 testing before prescribing abacavir, HLA-B*13:01 testing before prescribing co-trimoxazole and dapsone, and NAT2 testing before prescribing isoniazid) and 2) multiple-PGx testing as a combination of four single-gene PGx tests in one panel, were all compared to no PGx testing (current practice). To evaluate total cost in Thai baht (THB) and quality-adjusted life years (QALYs) for each strategy-based approach to a societal perspective, a hybrid decision tree and Markov model was constructed. Incremental cost-effectiveness ratios (ICERs) were estimated. Uncertainty, threshold, and scenario analyses were all performed.

Results

Before prescribing HIV therapy, providing single or multiple-PGx testing might save roughly 68 serious ADRs per year, and the number needed to screen (NNS) to avoid one serious ADR was 40. Consequently, approximately 35% and 40% of the cost of ADR treatment could be avoided by the implementation of single- and multiple-PGx testing, respectively. Compared with no PGx testing strategy, the ICERs were 146,319 THB/QALY gained for single-PGx testing and 152,014 THB/QALY gained for multiple-PGx testing. Moreover, the probability of multiple-PGx testing being cost-effective was 45% at the Thai willingness to pay threshold of 160,000 THB per QALY. Threshold analyses showed that multiple-PGx testing remained cost-effective under the range of cost, sensitivity at 0.95–1.00 and specificity at 0.98–1.00.

Conclusion

Single and multiple-PGx testing might be cost-effective options for reducing the incidence of drug-induced serious ADRs in people living with HIV.

PBPK Analysis to Study the Impact of Genetic Polymorphism of NAT2 on Drug-Drug Interaction Potential of Isoniazid

PURPOSE

Isoniazid (INH) is prescribed both for the prophylaxis as well as the treatment of tuberculosis. It is primarily metabolized through acetylation by a highly polymorphic enzyme, N-acetyl transferase 2 (NAT2), owing to which significant variable systemic drug levels have been reported among slow and rapid acetylators. Furthermore, many drugs, like phenytoin, diazepam, triazolam, etc., are known to show toxic manifestation when co-administered with INH and it happens prominently among slow acetylators. Additionally, it is revealed in in vitro inhibition studies that INH carries noteworthy potential to inhibit CYP2C19 and CYP3A4 enzymes. However, CYP inhibitory effect of INH gets masked by opposite enzyme-inducing effect of rifampicin, when used in combination. Thus, distinct objective of this study was to fill the knowledge gaps related to gene-drug-drug interactions (DDI) potential of INH when given alone for prophylactic purpose.

METHODS

Whole body-PBPK models of INH were developed and verified for both slow and fast acetylators. The same were then utilized to carry out prospective DDI studies with CYP2C19 and CYP3A4 substrates in both acetylator types.

RESULTS

The results highlighted likelihood of significant higher blood levels of CYP2C19 and CYP3A4 substrate drugs in subjects receiving INH pre-treatment. It was also re-established that interaction was more likely in slow acetylators, as compared to rapid acetylators.

CONCLUSION

The novel outcome of the present study is the indication that prescribers should give careful consideration while advising CYP2C19 and CYP3A4 substrate drugs to subjects who are on prophylaxis INH therapy, and are slow to metabolic acetylation.

Genetic characterization of N-acetyltransferase 2 variants in acquired multidrug-resistant tuberculosis in Indonesia

Background: Owing to the high resistance rate of tuberculosis (TB) to isoniazid, which is metabolized by N-acetyltransferase 2 (NAT2), we investigated the associations between NAT2 variants and multidrug-resistant (MDR)-TB. Materials & methods: The acetylator status based on NAT2 haplotypes of 128 patients with MDR-TB in Indonesia were compared with our published data from patients with anti-TB drug-induced liver injury (AT-DILI), TB and the general population. Results: NAT2*4 was more frequent in the MDR-TB group than in the AT-DILI group, TB controls and general controls. NAT2*4/*4 was significantly more frequent in patients with MDR-TB than in those with AT-DILI. NAT2*5B/7B, *6A/6A and *7B/*7B were detected at lower frequencies in patients with AT-DILI. Rapid acetylators were significantly more frequent in patients with MDR-TB than in those with AT-DILI. Conclusion: These results provide an initial data for optimizing TB treatment in the Indonesian population, and suggest that NAT2 genotyping may help to select appropriate treatment by predicting TB-treatment effect.

The Influence of NAT2 Genotypes on Isoniazid Plasma Concentration of Pulmonary Tuberculosis Patients in Southern Thailand

Background

Isoniazid (INH) is metabolized by polymorphic N-acetyltransferase 2 (NAT2) enzyme, which noticeably alters INH plasma concentration. We aimed to determine the distribution of NAT2 genotype in Thai tuberculosis (TB) patients and correlate their genotype with plasma INH concentrations.

Methods

Blood samples from 55 newly diagnosed pulmonary tuberculosis participants from three hospitals were collected to classify the subject by NAT2 genotype performed by the Multiplex haplotype-specific polymerase chain reaction method. Patients were grouped into three acetylators (fast, intermediate, and slow). On day 14 of tuberculosis treatment, the second blood sample was taken to estimate the peak plasma concentration at 2 hours after oral administration. INH plasma concentration was analyzed by liquid chromatography‒tandem mass spectrometry/mass spectrometry method.

Results

The NAT2 genotype distribution of fast, intermediate, and slow acetylator was 10.9%, 36.4%, and 52.7%, from six, 20, and 29 patients, respectively. The median (interquartile range) of INH plasma concentration at 2 hours post drug administration for these three genotypes were 0.75 (0.69–0.86), 2.56 (2.12–3.97), and 4.25 (3.56–5.50) µg/mL from four, 14, and 12 cases, respectively. The INH plasma concentration at 2 hours after administration was significantly associated with body weight and NAT2 acetylator.

Conclusion

The INH plasma concentration was found lower in fast than intermediate and slow acetylators. Body weight and NAT2 acetylator influenced INH plasma concentrations at 2 hours after drug administration. Therefore, the NAT2 genotype should be known before starting TB treatment to maximize therapeutic outcomes.

Association of slow acetylator genotype of N-acetyltransferase 2 with Parkinson's disease in south Indian population

AIM

Parkinson's Disease (PD) is a neurodegenerative disorder with predisposing genetic and environmental factors. The present study was undertaken to elucidate the possible association of NAT2 gene polymorphism in PD patients from south India.

METHODS

Using previously validated PCR-RFLP assays, we genotyped 105 PD subjects and 101 healthy controls for N-acetyl transferase (NAT2) gene polymorphism.

RESULTS

We observed a significantly elevated frequencies of NAT2 *5/6 (OR = 4.21; p < 0.029) and *5/7 (OR = 2.73; p < 0.025) genotypes and NAT2*5 (OR = 1.83; p < 0.039) allele among PD cases showing susceptible associations. The age at onset analysis revealed a significant association of NAT2 *4/6 (OR = 4.62; p < 0.05) genotype with early onset PD (EOPD). A positive association with early onset disease was observed for *5/7 (OR = 3.88; p < 0.075) genotype, however without statistical significance. Whereas, in late onset PD (LOPD) cases, significant susceptible association was observed for NAT2 *5/7 (OR = 5.27; p < 0.029) genotype. We observed a highly significant protective association of NAT2 *4/6 (OR = 0.27; p < 0.012) genotype and NAT2 *4 (OR = 0.52; p < 0.027) allele with LOPD. The acetylator status phenotype analysis have revealed a higher risk for, 'NAT2 slow acetylator' in both overall PD (OR = 2.39; p < 0.002) and LOPD (OR = 2.88; p < 0.007). However, 'NAT2 intermediate acetylator' with a lower risk in both overall PD (OR = 0.47; p < 0.011) and LOPD (OR = 0.36; p < 0.007) cases revealed protective associations.

CONCLUSIONS

Thus, our results revealed the possible susceptible association of NAT2 slow acetylator in PD pathogenesis in south Indian population.

Intermediate Susceptibility Dose-Dependent Breakpoints For High-Dose Rifampin, Isoniazid, and Pyrazinamide Treatment in Multidrug-Resistant Tuberculosis Programs

Background

Bacterial susceptibility is categorized as susceptible, intermediate-susceptible dose-dependent (ISDD), and resistant. The strategy is to use higher doses of first-line agents in the ISDD category, thereby preserving the use of these drugs. This system has not been applied to antituberculosis drugs. Pharmacokinetic/pharmacodynamic (PK/PD) target exposures, in tandem with Monte Carlo experiments, recently identified susceptibility breakpoints of 0.0312 mg/L for isoniazid, 0.0625 mg/L for rifampin, and 50 mg/L for pyrazinamide. These have been confirmed in clinical studies.

Methods

Target attainment studies were carried out using Monte Carlo experiments to investigate whether rifampin, isoniazid, and pyrazinamide dose increases would achieve the PK/PD target in >90% of 10000 patients with tuberculosis caused by bacteria, revealing minimum inhibitory concentrations (MICs) between the proposed and the traditional breakpoints.

Results

We found that an isoniazid dose of 900 mg/day identified a new ISDD MIC range of 0.0312-0.25 mg/L and resistance at MIC ≥0.5 mg/L. Rifampin 1800 mg/day would result in an ISDD of 0.0625-0.25 mg/L and resistance at MIC ≥0.5 mg/L. At a dose of pyrazinamide 4 g/day, the ISDD MIC range was 37.5-50 mg/L and resistance at MIC ≥100 mg/L. Based on MIC distributions, 93% (isoniazid), 78% (rifampin), and 27% (pyrazinamide) of isolates would be within the ISDD range.

Conclusions

Drug susceptibility testing at 2 concentrations delineating the ISDD range, and subsequently using higher doses, could prevent switching to a more toxic second-line treatment. Confirmatory clinical studies would provide evidence to change treatment guidelines.

Modelling the long-acting administration of anti-tuberculosis agents using PBPK: a proof of concept study

SETTING

Anti-tuberculosis formulations necessitate uninterrupted treatment to cure tuberculosis (TB), but are characterised by suboptimal adherence, which jeopardises therapeutic efficacy. Long-acting injectable (LAI) formulations or implants could address these associated issues.

OBJECTIVE

niazid, rifapentine, bedaquiline and delamanid-in adults for treatment for latent tuberculous infection (LTBI).

DESIGN

PBPK models were developed and qualified against available clinical data by integrating drug physicochemical properties and in vitro and population pharmacokinetic data into a mechanistic description of drug distribution. Combinations of optimal dose and release rates were simulated such that plasma concentrations were maintained over the epidemiological cut-off or minimum inhibitory concentration for the dosing interval.

RESULTS

The PBPK model identified 1500 mg of delamanid and 250 mg of rifapentine as sufficient doses for monthly intramuscular administration, if a formulation or device can deliver the required release kinetics of 0.001-0.0025 h-1 and 0.0015-0.0025 h-1, respectively. Bedaquiline and isoniazid would require weekly to biweekly intramuscular dosing.

CONCLUSION

We identified the theoretical doses and release rates of LAI anti-tuberculosis formulations. Such a strategy could ease the problem of suboptimal adherence provided the associated technological complexities for LTBI treatment are addressed.

N-acetyltransferase gene polymorphisms & plasma isoniazid concentrations in patients with tuberculosis

Background & objectives:

Variations in the N-acetyltransferase (NAT2) gene among different populations could affect the metabolism and disposition of isoniazid (INH). This study was performed to genotype NAT2 gene polymorphisms in tuberculosis (TB) patients from Chennai, India, and compare plasma INH concentrations among the different genotypes.

Methods:

Adult patients with TB treated in the Revised National TB Control Programme (RNTCP) in Chennai, Tamil Nadu, were genotyped for NAT2 gene polymorphism, and two-hour post-dosing INH concentrations were compared between the different genotypes. Plasma INH was determined by high-performance liquid chromatography. Genotyping of the NAT2 gene polymorphism was performed by real-time polymerase chain reaction method.

Results:

Among the 326 patients genotyped, there were 189 (58%), 114 (35%) and 23 (7%) slow, intermediate and fast acetylators, respectively. The median two-hour INH concentrations in slow, intermediate and fast acetylators were 10.2, 8.1 and 4.1 μg/ml, respectively. The differences in INH concentrations among the three genotypes were significant (P<0.001).

Interpretation & conclusions:

Genotyping of TB patients from south India for NAT2 gene polymorphism revealed that 58 per cent of the study population comprised slow acetylators. Two-hour INH concentrations differed significantly among the three genotypes.

The challenges of pharmacokinetic variability of first-line anti-TB drugs

INTRODUCTION

Inter-individual variations in the pharmacokinetics (PK) of anti-TB drugs are known to occur, which could have important therapeutic implications in patient management. Areas covered: We compiled factors responsible for PK variability of anti-TB drugs reported from different settings that would give a better understanding about the challenges of PK variability of anti-TB medications. We searched PubMed data base and Google scholar from 1976 to the present using the key words 'Pharmacokinetics', 'pharmacokinetic variability', 'first-line anti-TB therapy', 'Rifampicin', 'Isoniazid', 'Ethambutol', 'Pyrazinamide', 'food', 'nutritional status', 'HIV', 'diabetes', 'genetic polymorphisms' and 'pharmacokinetic interactions'. We also included abstracts from scientific meetings and review articles. Expert commentary: A variety of host and genetic factors can cause inter-individual variations in the PK of anti-TB drugs. PK studies conducted in various settings have adopted different designs, PK sampling time points, drug estimation methodologies. Hence comparison and interpretation of these results should be done with caution More phamacogenomic studies in different patient populations are needed for further understanding.

Prevention of isoniazid toxicity by NAT2 genotyping in Senegalese tuberculosis patients

Isoniazid (INH), recommended by WHO (World Health Organization) in the treatment of tuberculosis (TB), is metabolized primarily by the genetically polymorphic N-acetyltransferase 2 (NAT2) enzyme. The human population is divided into three different phenotypic groups according to acetylation rate: slow, intermediate, and fast acetylators. The objective of this study was to explore the relationship between NAT2 genotypes and the serum concentrations of INH. Blood samples from 96 patients with TB were taken for the analysis. NAT2 polymorphisms on coding region were examined by polymerase chain reaction (PCR) direct sequencing; the acetylation status was obtained by measuring isoniazid (INH) and its metabolite, acetylisoniazid (AcINH) in plasma was obtained by using the liquid chromatography coupled to mass spectrometry. TB patients were distributed into two groups of fast and slow acetylators according to the acetylation index calculated based on the plasma concentration of INH in the 3rd hour (T3) after an oral dose. Our PCR analysis identified several alleles, where NAT2*4, NAT2*5A, NAT2*6A, and NAT2*13A were the most important. The concentrations of INH varied between 1.10 mg/L and 13.10 mg/L at the 3rd hour and between 0.1 and 9.5 mg/L at the 6th hour. The use of the acetylating index I₃ allowed the classification of tested patients into two phenotypic groups: slow acetylators (44.3% of TB patients), and rapid acetylators (55.7%). Patient’s acetylation profile provides valuable information on their therapeutic, pharmacological, and toxicological responses.

A Physiologically Based Pharmacokinetic Model of Isoniazid and Its Application in Individualizing Tuberculosis Chemotherapy

Due to its high early bactericidal activity, isoniazid (INH) plays an essential role in tuberculosis treatment. Genetic polymorphisms of N-acetyltransferase type 2 (NAT2) cause a trimodal distribution of INH pharmacokinetics in slow, intermediate, and fast acetylators. The success of INH-based chemotherapy is associated with acetylator and patient health status. Still, a standard dose recommended by the FDA is administered regardless of acetylator type or immune status, even though adverse effects occur in 5 to 33% of all patients. Slow acetylators have a higher risk of development of drug-induced toxicity, while fast acetylators and immune-deficient patients face lower treatment success rates. To mechanistically assess the trade-off between toxicity and efficacy, we developed a physiologically based pharmacokinetic (PBPK) model describing the NAT2-dependent pharmacokinetics of INH and its metabolites. We combined the PBPK model with a pharmacodynamic (PD) model of antimycobacterial drug effects in the lungs. The resulting PBPK/PD model allowed the simultaneous simulation of treatment efficacies at the site of infection and exposure to toxic metabolites in off-target organs. Subsequently, we evaluated various INH dosing regimens in NAT2-specific immunocompetent and immune-deficient virtual populations. Our results suggest the need for acetylator-specific dose adjustments for optimal treatment outcomes. A reduced dose for slow acetylators substantially lowers the exposure to toxic metabolites and thereby the risk of adverse events, while it maintains sufficient treatment efficacies. Vice versa, intermediate and fast acetylators benefit from increased INH doses and a switch to a twice-daily administration schedule. Our analysis outlines how PBPK/PD modeling may be used to design and individualize treatment regimens.

Optimizing treatment outcome of first-line anti-tuberculosis drugs: the role of therapeutic drug monitoring

INTRODUCTION

Tuberculosis (TB) remains one of the world's deadliest communicable diseases. Although cure rates of the standard four-drug (rifampicin, isoniazid, pyrazinamide, ethambutol) treatment schedule can be as high as 95-98 % under clinical trial conditions, success rates may be much lower in less well resourced countries. Unsuccessful treatment with these first-line anti-TB drugs may lead to the development of multidrug resistant and extensively drug resistant TB. The intrinsic interindividual variability in the pharmacokinetics (PK) of the first-line anti-TB drugs is further exacerbated by co-morbidities such as HIV infection and diabetes.

METHODS

Therapeutic drug monitoring has been proposed in an attempt to optimize treatment outcome and reduce the development of drug resistance. Several studies have shown that maximum plasma concentrations (C max), especially of rifampicin and isoniazid, are well below the proposed target C max concentrations in a substantial fraction of patients being treated with the standard four-drug treatment schedule, even though treatment's success rate in these studies was typically at least 85 %.

DISCUSSION

The proposed target C max concentrations are based on the concentrations of these agents achieved in healthy volunteers and patients receiving the standard doses. Estimation of C max based on one or two sampling times may not have the necessary accuracy since absorption rate, especially for rifampicin, may be highly variable. In addition, minimum inhibitory concentration (MIC) variability should be taken into account to set clinically meaningful susceptibility breakpoints. Clearly, there is a need to better define the key target PK and pharmacodynamic (PD) parameters for therapeutic drug monitoring (TDM) of the first-line anti-TB drugs to be efficacious, C max (or area under the curve (AUC)) and C max/MIC (or AUC/MIC).

CONCLUSION

Although TDM of first-line anti-TB drugs has been successfully used in a limited number of specialized centers to improve treatment outcome in slow responders, a better characterization of the target PK and/or PK/PD parameters is in our opinion necessary to make it cost-effective.

Population pharmacokinetic analysis of isoniazid, acetylisoniazid, and isonicotinic acid in healthy volunteers

In this study, we aimed to quantify the effects of the N-acetyltransferase 2 (NAT2) phenotype on isoniazid (INH) metabolism in vivo and identify other sources of pharmacokinetic variability following single-dose administration in healthy Asian adults. The concentrations of INH and its metabolites acetylisoniazid (AcINH) and isonicotinic acid (INA) in plasma were evaluated in 33 healthy Asians who were also given efavirenz and rifampin. The pharmacokinetics of INH, AcINH, and INA were analyzed using nonlinear mixed-effects modeling (NONMEM) to estimate the population pharmacokinetic parameters and evaluate the relationships between the parameters and the elimination status (fast, intermediate, and slow acetylators), demographic status, and measures of renal and hepatic function. A two-compartment model with first-order absorption best described the INH pharmacokinetics. AcINH and INA data were best described by a two- and a one-compartment model, respectively, linked to the INH model. In the final model for INH, the derived metabolic phenotypes for NAT2 were identified as a significant covariate in the INH clearance, reducing its interindividual variability from 86% to 14%. The INH clearance in fast eliminators was 1.9- and 7.7-fold higher than in intermediate and slow eliminators, respectively (65 versus 35 and 8 liters/h). Creatinine clearance was confirmed as a significant covariate for AcINH clearance. Simulations suggested that the current dosing guidelines (200 mg for 30 to 45 kg and 300 mg for >45 kg) may be suboptimal (3 mg/liter ≤ Cmax ≤ 6 mg/liter) irrespective of the acetylator class. The analysis established a model that adequately characterizes INH, AcINH, and INA pharmacokinetics in healthy Asians. Our results refine the NAT2 phenotype-based predictions of the pharmacokinetics for INH.

Future of pharmacogenetics-based therapy for tuberculosis

Personalized medicine uses technology to enable a level of personalization not previously practical. Currently, tuberculosis (TB) therapy is not personalized. Previous reports have shown that a genetic polymorphism of NAT2 is associated with large interindividual and inter-racial differences in the toxicity and efficacy of isoniazid. Herein, we show the safety and efficacy of a pharmacogenetics-based standard TB therapy and also provide a schematic presentation that proposed therapeutic approaches for latent TB infection (LTBI) using NAT2 genotyping. Our data show that the pharmacogenetics-based TB therapy is safer and more efficacious than the standard therapy. Therefore, the therapy using NAT2 genotyping proposed for LTBI herein will be safer and more efficacious than the standard LTBI therapy. Introduction of this therapy with NAT2 genotyping will be one of the cornerstones of personalized medicine.

NAT2 genotype guided regimen reduces isoniazid-induced liver injury and early treatment failure in the 6-month four-drug standard treatment of tuberculosis: a randomized controlled trial for pharmacogenetics-based therapy

Objective

This study is a pharmacogenetic clinical trial designed to clarify whether the N-acetyltransferase 2 gene (NAT2) genotype-guided dosing of isoniazid improves the tolerability and efficacy of the 6-month four-drug standard regimen for newly diagnosed pulmonary tuberculosis.

Methods

In a multicenter, parallel, randomized, and controlled trial with a PROBE design, patients were assigned to either conventional standard treatment (STD-treatment: approx. 5 mg/kg of isoniazid for all) or NAT2 genotype-guided treatment (PGx-treatment: approx. 7.5 mg/kg for patients homozygous for NAT2*4: rapid acetylators; 5 mg/kg, patients heterozygous for NAT2*4: intermediate acetylators; 2.5 mg/kg, patients without NAT2*4: slow acetylators). The primary outcome included incidences of 1) isoniazid-related liver injury (INH-DILI) during the first 8 weeks of therapy, and 2) early treatment failure as indicated by a persistent positive culture or no improvement in chest radiographs at the8th week.

Results

One hundred and seventy-two Japanese patients (slow acetylators, 9.3 %; rapid acetylators, 53.5 %) were enrolled in this trial. In the intention-to-treat (ITT) analysis, INH-DILI occurred in 78 % of the slow acetylators in the STD-treatment, while none of the slow acetylators in the PGx-treatment experienced either INH-DILI or early treatment failure. Among the rapid acetylators, early treatment failure was observed with a significantly lower incidence rate in the PGx-treatment than in the STD-treatment (15.0 % vs. 38 %). Thus, the NAT2 genotype-guided regimen resulted in much lower incidences of unfavorable events, INH-DILI or early treatment failure, than the conventional standard regimen.

Conclusion

Our results clearly indicate a great potential of the NAT2 genotype-guided dosing stratification of isoniazid in chemotherapy for tuberculosis.

Gene dose effect of NAT2 variants on the pharmacokinetics of isoniazid and acetylisoniazid in healthy Chinese subjects

BACKGROUND

The aim of this study was to elucidate the gene dose effect of NAT2 and the effect on the pharmacokinetics of isoniazid (INH) and its metabolites acetylisoniazid (AcINH) in Chinese subjects.

METHODS

A total of 24 healthy Chinese subjects, consisting of eight homozygous wild types (wt/wt), eight heterozygous mutants (m/wt) and eight homozygous mutants (m/m) for NAT2, were enrolled in the study. The blood samples (0-14 h) of the subjects were taken after oral administration of a single dose (300 mg) of INH. Concentrations of INH and AcINH in plasma were measured by a reversed-phase HPLC method.

RESULTS

The ratio of AcINH and INH (R(A/I)) 3 h post-dose of wt/wt, m/wt and m/m groups were 3.22 ± 1.34, 1.35 ± 0.20 and 0.22 ± 0.06, respectively (p<0.01). The area under concentration-time curve (AUC) values of three groups were 10.35 ± 2.12, 16.34 ± 3.05, 42.24 ± 8.51 mg/h/L for INH and 42.19 ± 8.80, 38.05 ± 5.32, 19.78 ± 3.72 mg/h/L for AcINH, respectively (p<0.01). There was a good linear relationship between pharmacokinetic parameters and the number of active NAT2 genes.

CONCLUSIONS

The results suggest that there is a conspicuous gene dose effect in the pharmacokinetics of INH and AcINH. This finding may be valuable in the personalized therapy of tuberculosis with INH.

Hepatotoxic effects of therapies for tuberculosis

Hepatotoxic effects attributable to antituberculosis therapy are considered unique among drug-related liver problems because almost all first-line antituberculosis medications have such adverse effects, which vary in severity according to the drug and the regimen. In addition, all regimens for the treatment of active tuberculosis include a combination of medications that must typically be administered for at least 6 months to ensure complete cure of the disease and to minimize the development of drug-resistant bacterial strains. Hepatotoxic effects are a serious problem in patients who are undergoing treatment for tuberculosis, not only because of the morbidity and mortality they directly cause, but also because the liver symptoms can necessitate interruption of therapy or affect a patient's adherence to it, which can limit the efficacy of the antitubercular regimen.

Genetic variations of NAT2 and CYP2E1 and isoniazid hepatotoxicity in a diverse population

AIMS

TB is a serious global public health problem. Isoniazid, a key drug used to treat latent TB, can cause hepatotoxicity in some patients. This pilot study investigated the effects of genetic variation in NAT2 and CYP2E1 on isoniazid-induced hepatotoxicity in TB contacts in British Columbia, Canada.

MATERIALS & METHODS

DNA re-sequencing was used to establish the spectrum of genetic variation in the exons, promoter and conserved regions of NAT2 in all subjects. For CYP2E1, the CYP2E1*1C polymorphism was genotyped by PCR-RFLP. Association tests of NAT2 variants and haplotypes, as well acetylator types were performed.

RESULTS

We enrolled 170 subjects on isoniazid treatment (23 cases and 147 controls). Systematic re-sequencing of NAT2 revealed 18 known and 10 novel variants.

CONCLUSION

No single genetic variant of NAT2 and CYP2E1 showed a significant association with isoniazid-induced hepatotoxicity in this highly heterogeneous population. There was evidence of a trend for increasing hepatotoxicity risk across the rapid, intermediate and slow acetylator groups (p = 0.08).

Pharmacogenetic tools for malaria and TB in the Developing World

Some of the largest therapeutic drug exposures in the planet involve drugs employed against malaria and TB, two main global infectious diseases. Amodiaquine for malaria and isoniazid for TB are two pivotal drugs in the management of these diseases. Both drugs have been associated with severe adverse events. Amodiaquine and isoniazid are metabolized polymorphically by CYP2C8 and N-acetyltransferase 2, respectively. The polymorphic genes coding for these enzymes presently represent the best candidates for the application of personal pharmacogenetics for these diseases. We review the main reasons for this view, while asking the pivotal question of whether it is presently possible for pharmacogenetic-based personalized medicine to be applied in the malaria and TB settings of the Developing World.

Polymorphisms of promoter and coding regions of the arylamine N-acetyltransferase 2 (NAT2) gene in the Indonesian population: proposal for a new nomenclature

Polymorphisms of arylamine N-acetyltransferase 2 (NAT2) are reportedly associated with the risk of drug toxicities and development of various diseases. The present study examined NAT2 polymorphisms in both promoter and coding regions in the Indonesian population using PCR direct sequencing. The promoter and coding regions of NAT2 displayed 23 polymorphisms/variations, including eight new ones. Seven haplotypes in the promoter region and six haplotypes in the coding region were inferred. The haplotypes in promoter and coding regions showed limited combinations, and 13 combined haplotypes were inferred. The most frequent haplotypes were U1 (38.9%), U2 (33.5%) in the promoter region and NAT2*4 (37.3%), NAT2*6A (36.8%) in the coding region. When converted to predicted phenotypes, the studied population comprised 65.4% rapid acetylators and 35.6% slow acetylators according to bimodal distribution. According to trimodal distribution, frequencies of predicted phenotypes were 13.6, 50.8 and 35.6% for rapid, intermediate and slow acetylators, respectively. Frequencies of NAT2 alleles for the Indonesian population resembled those of other Southeast Asian populations. We also propose a new NAT2 nomenclature composed of haplotypes in the promoter region and conventional NAT2 haplotypes in the coding region, symbolized by NAT2*4.U1, NAT2*4.U2, NAT2*4.U3, NAT2*4.U5, NAT2*4.U6, NAT2*4.U7, NAT2*6A.U1, NAT2*7B.U2, NAT2*7B.U3, NAT2*5B.U1, NAT2*5B.U4, NAT2*12A.U4 and NAT2*13.U1.