Clinical significance of 2 h plasma concentrations of first-line anti-tuberculosis drugs: a prospective observational study

Study of risk factors and clinical management of patients with clinical non-response due to low plasma levels of anti-tubercular drugs

This study was carried out to assess the role of therapeutic drug monitoring of crucial first-line anti-tubercular drugs: rifampicin (R) and isoniazid (H) among 75 non-responding proven drug-sensitive tuberculosis patients on treatment followed by intervention in field conditions. The intervention was done in the form of either an increase in the dosage of R and H in patients with minimally low drug levels or a modification of the regimen in a certain group of patients with significantly low drug levels by augmenting it with three or four second-line drugs in addition to standard first-line drugs. This study also aimed to determine the relationship between the measured plasma concentration of anti-tubercular drugs and various demographic, microbiological, radiological, and malabsorption factors and the presence of co-morbidities affecting them. The study also focused on the clinical impact of the intervention for low plasma levels of anti-TB drugs on TB treatment outcomes. In our study overall, 85.5% of patients had low levels of any drug. In 85.3% of patients, R levels were low, and in 39.1%, H levels were low. On univariate analysis, low body mass index (BMI), hypoalbuminemia, bilateral disease on chest X-rays, and the presence of cavities were found to be significantly associated with low drug levels, while none of the factors were independently significantly associated. Low BMI, pulmonary tuberculosis and disseminated tuberculosis, far-advanced disease and bilateral disease on chest X-ray, presence of cavities, and only low R levels were associated with unfavorable outcomes, with none of the factors found to be significant on multivariate analysis. In our study, it was seen that the treatment outcome was favorable in 59.6% of patients in whom this intervention was done by augmenting the treatment regimen with three/four second-line drugs along with increasing the dose of R and H. To conclude, various factors may be associated with low plasma levels of anti-tubercular drugs. If such patients show clinical non-response after >6 months of treatment and have significantly low drug levels, with an absence of drug resistance, their treatment regimen may need augmentation with three/four second-line drugs along with an increase in the dose of R and H, which may lead to a favorable outcome.

Effects of sub-inhibitory concentrations of nafcillin, vancomycin, ciprofloxacin, and rifampin on biofilm formation of clinical methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) infections are often difficult to treat because of their biofilm-forming ability and antimicrobial resistance. We investigated the effects of sub-minimal inhibitory concentrations (MICs) of antibiotics on MRSA biofilm formation. Clinical MRSA isolates were grown with sub-MICs (1/256-1/2 × MICs) of nafcillin, vancomycin, ciprofloxacin, and rifampin. The biofilm biomass was measured using crystal violet staining. Of the 107 MRSA isolates tested, 63 (58.9%) belonged to sequence type 5 (ST5), and 44 (41.1%) belonged to ST72. The MIC50/MIC90 values of nafcillin, vancomycin, ciprofloxacin, and rifampin were 256/512, 1/2, 64/512, and 0.008/0.03 mg/L, respectively. The sub-MICs of nafcillin, vancomycin, ciprofloxacin, and rifampin promoted biofilm formation in 75 (70.1%), 49 (45.8%), 89 (83.2%), and 89 (83.2%) isolates, respectively. At sub-MICs of nafcillin, the factors associated with strong biofilm induction were the ST5 strain (P = 0.001) and agr dysfunction (P = 0.005). For the sub-MICs of ciprofloxacin, the associated factors were the ST5 strain (P = 0.002), staphylococcal protein A type t002 strain (P < 0.001), and ciprofloxacin resistance (P < 0.001). Among the sub-MICs of rifampin, only ST5 was associated with strong biofilm induction (P = 0.006). Because the sub-MICs of rifampin were much lower than clinically relevant concentrations, we further tested the capability of biofilm induction in 0.03[Formula: see text]32 mg/L of rifampin. At these concentrations, rifampin-induced biofilm formation was rare in rifampin-susceptible MRSA [1.0% (1 of 100)] but common in rifampin-resistant MRSA [71.4% (5 of 7), P < 0.001]. Induction of biofilm biomass at sub-MICs of antibiotics is common in clinical MRSA isolates and is differentially affected by the MRSA strain and antibiotic class.

IMPORTANCE

Bacteria can be exposed to sub-MICs of antibiotics at the beginning and end of a dosing regimen, between doses, or during low-dose therapies. Growing evidence suggests that sub-MICs of antimicrobials can stimulate MRSA biofilm formation and alter the composition of the biofilm matrix. Pevious studies have found that sub-MICs of oxacillin, methicillin, and amoxicillin promote biofilm formation in some community-acquired MRSA (CA-MRSA). We evaluated biofilm induction by sub-MICs of four different classes of antibiotics in 44 CA-MRSA and 63 healthcare-associated MRSA (HA-MRSA) strains. Our study indicated that sub-MICs of nafcillin, vancomycin, ciprofloxacin, and rifampin frequently promote biofilm induction in clinical MRSA isolates. Strong biofilm induction in sub-MICs of nafcillin, ciprofloxacin, and rifampin was more frequent in HA-MRSA than in CA-MRSA. Antibiotic-induced biofilm formation depends on the antibiotic class, MRSA strain, and antibiotic resistance. Our results emphasize the importance of maintaining effective bactericidal concentrations of antibiotics to treat biofilm-related infections.

Efficacy, safety, and pharmacokinetics of isoniazid affected by NAT2 polymorphisms in patients with tuberculosis: A systematic review

N-acetyltransferase 2 (NAT2) genetic polymorphisms might alter isoniazid metabolism leading to toxicity. We reviewed the impact of NAT2 genotype status on the pharmacokinetics, efficacy, and safety of isoniazid, a treatment for tuberculosis (TB). A systematic search for research articles published in Scopus, PubMed, and Embase until August 31, 2023, was conducted without filters or limits on the following search terms and Boolean operators: "isoniazid" AND "NAT2." Studies were selected if NAT2 phenotypes with pharmacokinetics or efficacy or safety of isoniazid in patients with TB were reported. Patient characteristics, NAT2 status, isoniazid pharmacokinetic parameters, early treatment failure, and the prevalence of drug-induced liver injury were extracted. If the data were given as a median, these values were standardized to the mean. Forty-one pharmacokinetics and 53 safety studies were included, but only one efficacy study was identified. The average maximum concentrations of isoniazid were expressed as supratherapeutic concentrations in adults (7.16 ± 4.85 μg/mL) and children (6.43 ± 3.87 μg/mL) in slow acetylators. The mean prevalence of drug-induced liver injury was 36.23 ± 19.84 in slow acetylators, which was significantly different from the intermediate (19.49 ± 18.20) and rapid (20.47 ± 20.68) acetylators. Subgroup analysis by continent showed that the highest mean drug-induced liver injury prevalence was in Asian slow acetylators (42.83 ± 27.61). The incidence of early treatment failure was decreased by genotype-guided isoniazid dosing in one study. Traditional weight-based dosing of isoniazid in most children and adults yielded therapeutic isoniazid levels (except for slow acetylators). Drug-induced liver injury was more commonly observed in slow acetylators. Genotype-guided dosing may prevent early treatment failure.

Correlation between serum isoniazid concentration and therapeutic response in patients of pulmonary tuberculosis in Central India: A prospective observational study

BACKGROUND

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis is one of the top ten causes of death worldwide. Isoniazid (INH) is an important component of anti-tuberculosis therapy (ATT). Low isoniazid levels can serve as a risk factor for the development of treatment failure, relapse of disease and acquired secondary resistance. Hence, serum level of isoniazid becomes a critical factor in determining the treatment outcome of patients on ATT. This study aimed to evaluate the correlation between serum isoniazid concentration and therapeutic response in patients of pulmonary tuberculosis in Central India.

METHODS

This was a prospective single cohort observational study conducted at a tertiary care hospital. Therapeutic response in newly diagnosed patients of pulmonary TB was determined based the microbiological, clinical and radiological parameters. Serum INH levels were estimated based on a spectrophotometric method using nano-spectrophotometer.

RESULTS

In this study, patients had a significant improvement in treatment outcome as evident by a significant decrease in the TB score I at end of IP (p = 0.001) and a significant decline in the Timika score at end of CP (p = 0.001). Although all patients converted to sputum negative at end of CP, 20% remained positive at end of IP. Lower INH levels were seen in 13.3% of the study population. Higher INH levels were observed in sputum converters, patients with low TB score I and low Timika score, although no statistically significant difference was noted (p > 0.05).

CONCLUSION

In this study, we could not find any statistically significant association between serum INH levels and therapeutic outcome of the patients. Further studies on a larger population could provide better understanding about the prevalence of low serum isoniazid levels among the Indian population and establish its relationship with therapeutic outcome. Also, the usage of a comparatively less expensive spectrophotometric method of analysis makes this feasible in almost every district hospital without the need of high-performance liquid chromatography which is costlier and needs more expertise.

Variability in plasma rifampicin concentrations and role of SLCO1B1, ABCB1, AADAC2 and CES2 genotypes in Ethiopian patients with tuberculosis

BACKGROUND

Rifampicin, a key drug against tuberculosis (TB), displays wide between-patient pharmacokinetics variability and concentration-dependent antimicrobial effect. We investigated variability in plasma rifampicin concentrations and the role of SLCO1B1, ABCB1, arylacetamide deacetylase (AADAC) and carboxylesterase 2 (CES-2) genotypes in Ethiopian patients with TB.

METHODS

We enrolled adult patients with newly diagnosed TB (n = 119) who had received 2 weeks of rifampicin-based anti-TB therapy. Venous blood samples were obtained at three time points post-dose. Genotypes for SLCO1B1 (c.388A > G, c.521T > C), ABCB1 (c.3435C > T, c.4036A > G), AADACc.841G > A and CES-2 (c.269-965A > G) were determined. Rifampicin plasma concentration was quantified using LC-MS/MS. Predictors of rifampicin Cmax and AUC0-7 h were analysed.

RESULTS

The median rifampicin Cmax and AUC0-7 were 6.76 µg/mL (IQR 5.37-8.48) and 17.05 µg·h/mL (IQR 13.87-22.26), respectively. Only 30.3% of patients achieved the therapeutic efficacy threshold (Cmax>8 µg/mL). The allele frequency for SLCO1B1*1B (c.388A > G), SLCO1B1*5 (c.521T > C), ABCB1 c.3435C > T, ABCB1c.4036A > G, AADAC c.841G > A and CES-2 c.269-965A > G were 2.2%, 20.2%, 24.4%, 14.6%, 86.1% and 30.6%, respectively. Sex, rifampicin dose and ABCB1c.4036A > G, genotypes were significant predictors of rifampicin Cmax and AUC0-7. AADACc.841G > A genotypes were significant predictors of rifampicin Cmax. There was no significant influence of SLCO1B1 (c.388A > G, c.521T > C), ABCB1c.3435C > T and CES-2 c.269-965A > G on rifampicin plasma exposure variability.

CONCLUSIONS

Subtherapeutic rifampicin plasma concentrations occurred in two-thirds of Ethiopian TB patients. Rifampicin exposure varied with sex, dose and genotypes. AADACc.841G/G and ABCB1c.4036A/A genotypes and male patients are at higher risk of lower rifampicin plasma exposure. The impact on TB treatment outcomes and whether high-dose rifampicin is required to improve therapeutic efficacy requires further investigation.

The Role of Therapeutic Drug Monitoring in Slow Response Extra-Pulmonary Tuberculosis Treatment: A Case Report

Tuberculosis is caused by an infectious bacterium and it has significant morbidity and mortality rates globally. It mostly affects the lungs, but it can also spread to other parts of the body, like the lymph nodes (tuberculous lymphadenitis). The most common way to treat it is with the RIPE regimen, which includes rifampin, isoniazid, pyrazinamide, and ethambutol. The drugs can be slowly or rapidly metabolized, resulting in either increased toxicity or subtherapeutic drug levels. In this paper, we discuss the case of a slow responder who was treated with increased rifampin and isoniazid doses and improved clinically and biochemically. It's the first case of a slow responder diagnosed with tuberculous lymphadenitis reported in the Gulf region.

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.

Correlations among the plasma concentrations of first-line anti-tuberculosis drugs and the physiological parameters influencing concentrations

Background: The plasma concentrations of the four most commonly used first-line anti-tuberculosis (TB) drugs, isoniazid (INH), rifampicin (RMP), ethambutol (EMB), and pyrazinamide (PZA), are often not within the therapeutic range. Insufficient drug exposure could lead to drug resistance and treatment failure, while excessive drug levels may lead to adverse reactions. The purpose of this study was to identify the physiological parameters influencing anti-TB drug concentrations. Methods: A retrospective cohort study was conducted. The 2-h plasma concentrations of the four drugs were measured by using the high-performance liquid chromatography-tandem mass spectrometry method. Results: A total of 317 patients were included in the study. The proportions of patients with INH, RMP, EMB, and PZA concentrations within the therapeutic range were 24.3%, 31.5%, 27.8%, and 18.6%, respectively. There were positive associations between the concentrations of INH and PZA and RMP and EMB, but negative associations were observed between the concentrations of INH and RMP, INH and EMB, RMP and PZA, and EMB and PZA. In the multivariate analysis, the influencing factors of the INH concentration were the PZA concentration, total bile acid (TBA), serum potassium, dose, direct bilirubin, prealbumin (PA), and albumin; those of the RMP concentration were PZA and EMB concentrations, weight, α-l-fucosidase (AFU), drinking, and dose; those of the EMB concentration were the RMP and PZA concentrations, creatinine, TBA and indirect bilirubin; and those of the PZA concentration were INH, RMP and EMB concentrations, sex, weight, uric acid and drinking. Conclusion: The complex correlations between the concentrations of the four first-line anti-TB drugs lead to a major challenge in dose adjustment to maintain all drugs within the therapeutic window. Levels of TBA, PA, AFU, and serum potassium should also be considered when adjusting the dose of the four drugs.

Clinical impact of plasma concentrations of first-line antituberculosis drugs

BACKGROUND

The clinical significance of low antituberculosis (anti-TB) drug concentrations has not been fully elucidated.

OBJECTIVES

To investigate the clinical consequences of first-line drug concentrations in adult patients with drug-susceptible pulmonary TBin South Africa (SA).

METHOD

We conducted a pharmacokinetic study nested within the control arm of the Improving Treatment Success (IMPRESS) trial(NCT02114684) in Durban, SA. During the first 2 months of treatment, participants received weight-based dosing of first-line anti-TBdrugs (rifampicin, isoniazid, pyrazinamide and ethambutol), and had plasma drug concentrations measured at 2 and 6 hours after drugadministration during the 8th week of treatment. Intermediate (8 weeks), end-of-treatment (6 months) and follow-up TB outcomes wereassessed using World Health Organization criteria.

RESULTS

We measured plasma drug concentrations on available samples in 43 participants. Peak drug concentrations were below thetherapeutic range in 39/43 (90.7%) for rifampicin, 32/43 (74.4%) for isoniazid, 27/42 (64.3%) for pyrazinamide and 5/41 (12.2%) forethambutol. At the end of the intensive phase of treatment (week 8), 20.9% (n=9/43) of participants remained culture positive. We did notfind a relationship between the concentrations of first-line drugs and treatment outcomes at week 8. All participants were cured at the endof treatment, and there were no relapses during the 12-month follow-up period.

CONCLUSION

Treatment outcomes were favourable despite low drug concentrations as defined by current reference thresholds.

Plasma drug concentrations of 4-drug fixed-dose combination regimen and its efficacy for treatment of pulmonary tuberculosis under National Tuberculosis Elimination Programme: A prospective pilot study

BACKGROUND

The thrice weekly dosing regimen of DOTS has shown low rifampicin plasma concentrations as an independent risk factor for unfavourable tuberculosis (TB) outcome. With introduction of daily regimen using fixed dose combinations (FDC) under National Tuberculosis Elimination Programme (NTEP) the existence of suboptimal plasma levels of first-line antitubercular drugs and its clinical significance remain poorly understood.

METHOD

We included a prospective cohort of newly diagnosed pulmonary tuberculosis (PTB) patients receiving 4-FDC daily regimen under NTEP. Plasma concentration at 2 hours (C_2h) of each drug was determined after two weeks of treatment using liquid chromatography (LCMS/MS) developed by us. TB card and laboratory reports were reviewed for baseline characteristics and clinical status at 2, 4 and 6 months after the initiation of treatment. At a 1 year follow-up, therapy failure was defined as death or a relapse of tuberculosis.

RESULTS

Among 40 PTB patients, the C_2h post dose plasma concentrations of H, R and E were suboptimal in 25%, 60% and 10% respectively. The C_2h of H, R, Z and E were respectively 4.2 ± 2.0, 7.3 ± 2.8, 39.2 ± 8.8 and 3.5 ± 1.2 μg/ml; 60% of the patients had suboptimal plasma concentrations and commonly it was observed with H and R. C_2h were lower than expected for at least two drugs i.e. H and R in 25% (10/40) of the patients. Plasma concentration of isoniazid and rifampicin has always been considered important for microbiological response and treatment outcome and low concentrations has been associated with poor treatment response. These patients may require a two year follow up and critical evaluation for prevention of MDR-TB. However, all the TB patients were cured and none of them had recurrence within one year follow up.

CONCLUSIONS

All the pulmonary TB patients administering 4-FDC daily regimen under programmatic settings were cured despite the suboptimal levels of isoniaizd and rifampicin. All the patients achieved pyrazinamide plasma levels and probably this could be the reason behind favourable outcome. Further study is required on large sample size with various subset of population to understand the need of therapeutic drug monitoring.

Very-Rapidly Dissolving Printlets of Isoniazid Manufactured by SLS 3D Printing: In Vitro and In Vivo Characterization

The focus of this research was to understand the effects of formulation and processing variables on the very-rapidly dissolving printlets of isoniazid (INH) manufactured by the selective laser sintering (SLS) three-dimensional (3D) printing method, and to characterize their physicochemical properties, stability, and pharmacokinetics. Fifteen printlet formulations were manufactured by varying the laser scanning speed (400-500 mm/s, X₁), surface temperature (100-110 °C, X₂), and croscarmellose sodium (CCS, %, X₃), and the responses measured were weight (Y₁), hardness (Y₂), disintegration time (DT, Y₃), and dissolution (Y₄). Laser scanning was the most important processing factor affecting the responses. DT was very rapid (≥3 s), and dissolution (>99%) was completed within 3 min. The root-mean-square error in the studied responses was low and analysis of variance (ANOVA) was statistically significant (p < 0.05). X-ray micro-computed tomography (micro-CT) images showed very porous structures with 24.6-34.4% porosity. X-ray powder diffraction and differential scanning calorimetry data indicated partial conversion of the crystalline drug into an amorphous form. The printlets were stable at 40 °C/75% RH with no significant changes in assay and dissolution. Pharmacokinetic profiles of the printlets and compressed tablets were superimposable. In conclusion, the rapidly dissolving printlets of the INH were stable, and oral bioavailability was similar to that of compositionally identical compressed tablets.

Semi-Automated Therapeutic Drug Monitoring as a Pillar toward Personalized Medicine for Tuberculosis Management

Standard tuberculosis (TB) management has failed to control the growing number of drug-resistant TB cases worldwide. Therefore, innovative approaches are required to eradicate TB. Model-informed precision dosing and therapeutic drug monitoring (TDM) have become promising tools for adjusting anti-TB drug doses corresponding with individual pharmacokinetic profiles. These are crucial to improving the treatment outcome of the patients, particularly for those with complex comorbidity and a high risk of treatment failure. Despite the actual benefits of TDM at the bedside, conventional TDM encounters several hurdles related to laborious, time-consuming, and costly processes. Herein, we review the current practice of TDM and discuss the main obstacles that impede it from successful clinical implementation. Moreover, we propose a semi-automated TDM approach to further enhance precision medicine for TB management.

A Simple and Sensitive UPLC–UV Method for Simultaneous Determination of Isoniazid, Pyrazinamide, and Rifampicin in Human Plasma and Its Application in Therapeutic Drug Monitoring

As the first-line clinical drugs for tuberculosis (TB), isoniazid (INH), pyrazinamide (PZA), and rifampicin (RMP) are playing important roles for preventing the rapid spread of TB. Precise quantification of these drugs in biological samples is crucial to evaluate or improve the efficacy of advanced TB drug delivery systems, which are designed for reducing drug resistance, minimizing side effects, etc. Herein, a simple and sensitive method based on UPLC–UV was established and investigated for simultaneous quantification of PZA, INH, and RMP in human plasma and was applied to anti-TB drug therapeutic drug monitoring. The analytes were implemented on an HSS T3 C18 column at 40°C. The separation was performed with a gradient elution with methanol–acetonitrile–water (3:3:94) at 0.1 ml/min. The analysis only involved plasma with a small volume of 100 µL and a rapid one-step protein precipitation with methanol–acetonitrile (1:1). The results showed that the calibration curves for INH, PZA, and RMP were linear in a range of 0.5–20 μg/ml, 5–60 μg/ml, and 5–60 μg/ml, respectively. The intra- and inter-day precisions were both smaller than 15%, and the lower limit of quantitation (LLOQ) was identifiable and reproducible at 0.5 μg/ml for INH and 5 μg/ml for both PZA and RMP, respectively. The target drugs in plasma were stable after 21 days of storage at −80°C. The results indicated that our developed method is suitable for the simultaneous monitoring of INH, PZA, and RMP in human plasma.

High intrapulmonary rifampicin and isoniazid concentrations are associated with rapid sputum bacillary clearance in patients with pulmonary tuberculosis

Background

Intrapulmonary pharmacokinetics may better explain response to tuberculosis (TB) treatment than plasma pharmacokinetics. We explored these relationships by modeling bacillary clearance in sputum in adult patients on first-line treatment in Malawi.

Methods

Bacillary elimination rates (BER) were estimated using linear mixed-effects modelling of serial time-to-positivity in mycobacterial growth indicator tubes for sputum collected during the intensive phase of treatment (weeks 0–8) for microbiologically confirmed TB. Population pharmacokinetic models used plasma and intrapulmonary drug levels at 8 and 16 weeks. Pharmacokinetic-pharmacodynamic relationships were investigated using individual-level measures of drug exposure (area-under-the-concentration-time-curve [AUC] and C_max) for rifampicin, isoniazid, pyrazinamide, and ethambutol, in plasma, epithelial lining fluid, and alveolar cells as covariates in the bacillary elimination models.

Results

Among 157 participants (58% human immunodeficiency virus [HIV] coinfected), drug exposure in plasma or alveolar cells was not associated with sputum bacillary clearance. Higher peak concentrations (C_max) or exposure (AUC) to rifampicin or isoniazid in epithelial lining fluid was associated with more rapid bacillary elimination and shorter time to sputum negativity. More extensive disease on baseline chest radiograph was associated with slower bacillary elimination. Clinical outcome was captured in 133 participants, with 15 (11%) unfavorable outcomes recorded (recurrent TB, failed treatment, or death). No relationship between BER and late clinical outcome was identified.

Conclusions

Greater intrapulmonary drug exposure to rifampicin or isoniazid in the epithelial lining fluid was associated with more rapid bacillary clearance. Higher doses of rifampicin and isoniazid may result in sustained high intrapulmonary drug exposure, rapid bacillary clearance, shorter treatment duration and better treatment outcomes.

Population Pharmacokinetics Analyses of Rifampicin in Adult and Children Populations: A Systematic Review

AIMS

Rifampicin has become an essential component as the first-line therapy for pulmonary tuberculosis (PTB). Several population pharmacokinetic (PK) studies on rifampicin in the adult and children population have been studied previously. Therefore, the aims of the systematic review were (i) to summarize the relevant published studies and significant covariates that influence the PK of rifampicin across different populations, (ii) to identify any knowledge gap that requires additional research in the future.

METHODS

A total of 121 relevant population PK articles were systematically identified using PubMed and Scopus from inception to October 2021. Review articles, in-vitro, and physiological methods, animal studies, and noncompartmental analysis were excluded.

RESULTS

19 studies which 16 involved adults, two involved children, and one involved both adults and children were included in the review. The structural model of rifampicin can be described as one compartment with a transient compartment absorption model and first-order elimination in most of the studies. Pharmaceutical formulation, body weight, gender, pregnancy status, diabetes, and nutritional supplementation were found to be the significant covariates that affect the PK parameters. External validation of the developed PK model was only conducted in two studies.

CONCLUSIONS

The source of variability for PK parameters of rifampicin remains inconsistent and poorly understood even though there were many potential covariates investigated in the selected studies. Exploring other possible factors and implementation a strict sampling strategy by considering the induction effects might unravel precise and reliable information. Furthermore, external validation should be frequently conducted to produce better predictability of model performance.

Real-life isoniazid and rifampicin plasma concentrations in children: a tool for therapeutic drug monitoring of tuberculosis

Background

Low plasma levels of first-line antitubercular drugs can be counted among the main causes of poor response to antitubercular therapy, and therapeutic drug monitoring has been proposed as a method to promote tailored treatments for both child and adult patients. The main aim of the study was to evaluate serum concentrations of isoniazid (INH) and rifampicin (RIF) and to investigate reasons for sub-therapeutic plasma concentrations in order to fix dosages.

Methods

Children with TB were prospectively enrolled from January to August 2019. Two venous blood samples were collected (the first at least 15 days after the beginning of antitubercular treatment, and the second between 1 and 8 weeks later). Plasma concentrations were determined by a validated high-performance liquid chromatography method.

Results

In all, 45 children were included. Seventy blood samples for INH plasma concentration were collected between 120 and 240 min after drug intake. Adjusting for dose (mg/kg/day) and time of INH administration, when considering three different age groups (≤ 2 years, 2–12 years, > 12 years), a statistically significant lower INH plasma concentration was observed in younger children compared to the older age groups in the multivariate analysis (p < 0.001 and p < 0.001). A total of 68 blood samples were evaluated for RIF concentrations. Both for INH and RIF a statistically significant lower plasma concentration was also observed in adolescents (p < 0.001). Fifteen children (15/45, 33%) presented drug concentrations under the referral therapeutic range.

Conclusions

Based on our findings, monitoring patients’ drug plasma concentrations in children under 2 years of age and in adolescents can make treatment more patient-tailored.

Effect of serum isoniazid level on treatment outcomes among tuberculosis patients with slow response - A retrospective cohort study

BACKGROUND

In this study, we investigate the effects of low serum TB drug level on treatment outcome among TB patients with slow response in South Korea, where the prevalence of rapid acetylator is relatively high.

METHODS

Among the pulmonary TB patients whose treatment outcomes were reported between 2014 and 2018 at Incheon St. Mary hospital, those who underwent TDM because of delayed culture conversion or reversion were included. Primary outcome was microbiological failure defined as (1) positive sputum culture after 120 days of treatment, or (2) culture-confirmed relapse within one year after treatment completion. Patients with culture conversion within 120 days and no relapse were classified as the final conversion group. Clinical characteristics and serum drug concentration at 2 h after administration (C_2hr) were compared between those two groups.

RESULTS

A total of 55 pulmonary TB patients were included. Prevalence of subtherapeutic range of C_2hr for isoniazid and rifampin was 78.2% and 21.8%, respectively. With one year of follow-up, 21 cases were classified as the microbiological failure group, and 34 cases as the final conversion group. In a multivariable logistic regression model for predicting microbiological failure, C_2hr of isoniazid was the most significant predictor after adjusting for the effects of age and sex (adjusted odds ratio, 0.29; p = 0.009). In a tree-based classification model, C_2hr of isoniazid with cutoff level 2.5 μg/ml was the most important variable for predicting microbiological failure.

CONCLUSIONS

Low serum isoniazid level was related to poor treatment outcomes among the TB patients with slow response.

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.

The Impact of First-Line Anti-Tubercular Drugs' Pharmacokinetics on Treatment Outcome: A Systematic Review

BACKGROUND

Tuberculosis remains the major public health problem besides tremendous efforts to combat it. Most tuberculosis patients are treated with a standard dose of first-line anti-TB drugs. The cure rate, however, varies from patient to patient. Various factors have been related to anti-TB treatment failure. In recent years, studies associating lower plasma concentrations of anti-TB drugs with poor treatment outcomes are emerging although the results are inconclusive.

OBJECTIVE

Investigate the impact of first-line anti-tubercular drugs pharmacokinetics on treatment outcome.

METHODS

A systematic search of Pubmed, EMBASE, Web of Science, and the Cochrane Library for articles published in the English language between January 2010 to June 2020 was conducted to identify eligible studies describing associations of first-line anti-tubercular drug pharmacokinetics with treatment outcomes. The primary outcomes considered were pharmacokinetics parameter results and its association with treatment outcome.

RESULTS

The search identified 1754 articles of which twelve articles; ten prospective observational studies and two controlled clinical trials fulfilled the eligibility criteria. The majority of the studies showed target concentrations for the first-line anti-tubercular drugs below the current standard range. Among the twelve studies, eleven studies assessed rifampicin pharmacokinetics of which eight reported association of drug concentration and treatment outcomes. Similarly, four out of eight and three out of seven reported drug concentration and treatment outcome association for isoniazid and pyrazinamide, respectively. Despite the low plasma concentration, a favorable treatment outcome was achieved for the bulk of the patients. Irrespective of the inconsistency, an increase in exposure to rifampicin improved the outcome, and lower rifampicin, isoniazid, and pyrazinamide concentration are associated with poor outcome. No data are available for ethambutol associating its pharmacokinetics with treatment outcomes.

CONCLUSION

The pharmacokinetics of first-line antitubercular drugs can influence treatment outcomes. Further controlled clinical studies are, however, required to establish these relationships.

Subtherapeutic Rifampicin Concentration Is Associated With Unfavorable Tuberculosis Treatment Outcomes

BACKGROUND

The relationships between first-line drug concentrations and clinically important outcomes among patients with tuberculosis (TB) remain poorly understood.

METHODS

We enrolled a prospective cohort of patients with new pulmonary TB receiving thrice-weekly treatment in India. The maximum plasma concentration of each drug was determined at months 1 and 5 using blood samples drawn 2 hours postdose. Subtherapeutic cutoffs were: rifampicin <8 µg/mL, isoniazid <3 µg/mL, and pyrazinamide <20 µg/mL. Factors associated with lower log-transformed drug concentrations, unfavorable outcomes (composite of treatment failure, all-cause mortality, and recurrence), and individual outcomes were examined using Poisson regression models.

RESULTS

Among 404 participants, rifampicin, isoniazid, and pyrazinamide concentrations were subtherapeutic in 85%, 29%, and 13%, respectively, at month 1 (with similar results for rifampicin and isoniazid at month 5). Rifampicin concentrations were lower with human immunodeficiency virus coinfection (median, 1.6 vs 4.6 µg/mL; P = .015). Unfavorable outcome was observed in 19%; a 1-μg/mL decrease in rifampicin concentration was independently associated with unfavorable outcome (adjusted incidence rate ratio [aIRR], 1.21 [95% confidence interval {CI}, 1.01-1.47]) and treatment failure (aIRR, 1.16 [95% CI, 1.05-1.28]). A 1-μg/mL decrease in pyrazinamide concentration was associated with recurrence (aIRR, 1.05 [95% CI, 1.01-1.11]).

CONCLUSIONS

Rifampicin concentrations were subtherapeutic in most Indian patients taking a thrice-weekly TB regimen, and low rifampicin and pyrazinamide concentrations were associated with poor outcomes. Higher or more frequent dosing is needed to improve TB treatment outcomes in India.

A simple and reliable analytical method for simultaneous quantification of first line antitubercular drugs in human plasma by LCMS/MS

The present study describes the optimization of a simple and reliable method for the determination of four first line antitubercular drugs in human plasma. The studied analytes were isoniazid (H), rifampicin (R), pyrazinamide (Z) and ethambutol (E) in fixed dose combination recommended to patients under the Revised National Tuberculosis Control Programme (RNTCP, India). The analytes were extracted from the human plasma (150 μL) using the single step liquid-liquid extraction approach and were analyzed by liquid chromatography (LC) coupled to tandem mass spectrometry (MS/MS). The method was fully validated, according to USFDA guidelines. A linear range of 0.05-10 μg mL^-1, 0.1-20 μg mL^-1, 0.5-100 μg mL^-1 and 0.05-10 μg mL^-1 for H, R, Z and E respectively was established, presenting determination coefficients above 0.99. Concerning imprecision, the CV was lower than 15% for all analytes. All tested analytes were found to be stable in the samples. Although the values obtained for recovery were above 85%, the method proved to be sensitive, since low detection limits of 0.05 μg mL^-1 for H and E, 0.1 μg mL^-1 for R and 0.5 μg mL^-1 for Z were obtained. The intra-day and inter-day accuracy and imprecision were within CV ±15%. The use of the conventional silica column in the extraction of these compounds through a single step protein precipitation method simplifies the analytical process. In addition due to its simplicity and sensitivity, it can be applied to carry out therapeutic drug monitoring and drug level assessment in human plasma samples. The results of analyte levels are comparable to other reported methods. The method had been successfully applied for simultaneous determination of first line anti-tubercular drugs in pulmonary tubercular patients. The method requires 150 μL of patient plasma and offers low volume for injection (10 μL) and blood sample collection (3 mL) which will be an added advantage for pediatric anti-TB drug level assessment and monitoring.

A public-private model to scale up diabetes mellitus screening among people accessing tuberculosis diagnostics in Dhaka, Bangladesh

Background:

Data are scarce regarding the prevalence of diabetes mellitus (DM) among tuberculosis (TB) patients in Bangladesh. This study was undertaken to estimate the number needed to screen (NNS) to identify a case of DM among those with TB symptoms and those with confirmed TB disease, and to identify factors predicting treatment outcomes of TB patients with and without DM.

Methods:

Persons attending public–private model screening centres in urban Dhaka for the evaluation of TB were offered free blood glucose testing in addition to computer-aided chest X-ray and sputum Xpert MTB/RIF.

Results:

Among 7647 people evaluated for both TB and DM, the NNS was 35 (95% confidence interval (CI) 31–40) to diagnose one new case of DM; among those diagnosed with TB, the NNS was 21 (95% CI 17–29). Among those with diagnosed TB, patients with DM were more likely to have cavitation on chest X-ray compared to those without DM (31% vs 22%). Treatment failure (odds ratio (OR) 18.9, 95% CI 5.43–65.9) and death (OR 2.08, 95% CI 1.11–3.90) were more common among TB patients with DM than among TB patients without DM. DM was the most important predictor of a poor treatment outcome in the classification analysis for TB patients aged 39 years and above.

Conclusions:

A considerable burden of DM was found among patients accessing TB diagnostics through a public–private model in urban Bangladesh, and DM was associated with advanced TB disease and a high rate of poor treatment outcome.

Development and Application of a LC-MS/MS Method for Simultaneous Quantification of Four First-Line Antituberculosis Drugs in Human Serum

A simple, rapid, and sensitive liquid chromatography (LC)/mass spectrometry (MS) method was established and validated for simultaneous quantitation of pyrazinamide, isoniazid, rifampicin, and ethambutol in human blood sample. Samples were pretreated by a single-step precipitation with acetonitrile. Chromatographic separation was achieved on XSelecT HSS T3 column by gradient elution with a total run time of 5.0 min. MS detection was performed by a triple quadrupole tandem mass spectrometer in the multiple reaction monitoring mode with a positive electrospray ionization source. Isotope-labeled internal standard, especially rifampicin-D8, was applied to adjust for the loss during sample treatment. The established LC-MS/MS method showed a wide analytical range (pyrazinamide: 1.02∼60.0 μg/mL, isoniazid: 0.152∼10.0 μg/mL, rifampicin: 0.500∼30.0 μg/mL, and ethambutol: 0.0998∼5.99 μg/mL) and a good linearity (r > 0.99 for the four analytes) with acceptable accuracy and precision (90.15%∼104.62% and 94.00%∼104.02% for intra- and interaccuracy, respectively; RSD%: <12.46% and <6.43% for intra- and interprecision, respectively). It also showed excellent recoveries (79.24%∼94.16% for all analytes) and absence of significant matrix effect. This method was successfully applied to the quantification of four first-line antituberculosis (anti-TB) drugs, suggesting its suitability for therapeutic drug monitoring in the clinical practices.

Determinants of serum concentration of first-line anti-tuberculosis drugs from China

Therapeutic drug monitoring has been employed in anti-tuberculosis (TB) drugs to assess optimal dose for maximum therapeutic effects and minimal toxicity. But the determinants of serum concentration need further evidences.In a retrospective case-control study, clinical and laboratory data were collected from 717 in-patients with TB at Xi'an Chest Hospital, China. Two hours serum concentrations of isoniazid, rifampicin, pyrazinamide as well as ethambutol were obtained and analyzed by liquid chromatography-tandem mass spectrometry.The month 2 culture conversion group had lower concentration of isoniazid, pyrazinamide, and ethambutol than month 1 group. Statistical analysis showed that serum concentrations of isoniazid, rifampicin, pyrazinamide, and ethambutol revealed a positive relationship with dose (mg/kg) (P < .001, P < .001, P < .001, and P = .003, respectively). Furthermore, isoniazid concentration was related to smoking (P = .009) and prior TB (P = .011), while rifampicin and pyrazinamide concentrations were correlated to sex (P = .004 and 0.025, respectively). Ethambutol concentration was associated with creatinine clearance (Ccr, P = .002).It is necessary to optimize drug doses using therapeutic drug monitoring while considering the following determinants: weight, smoking status, prior TB, sex, and Ccr. Furthermore, low 2 hours serum concentrations can be associated with longer culture conversion.

Distribution of plasma concentrations of first-line anti-TB drugs and individual MICs: a prospective cohort study in a low endemic setting

Background

Therapeutic drug monitoring (TDM) could improve current TB treatment, but few studies have reported pharmacokinetic data together with MICs.

Objectives

To investigate plasma concentrations of rifampicin, isoniazid, pyrazinamide and ethambutol along with MICs.

Methods

Drug concentrations of rifampicin, isoniazid, pyrazinamide and ethambutol were analysed pre-dose and 2, 4 and 6 h after drug intake at week 2 in 31 TB patients and MICs in BACTEC 960 MGIT were determined at baseline. The highest plasma concentrations at 2, 4 and 6 h post-dose (Chigh) were determined, as well as estimates of Chigh/MIC and area under the concentration-time curve (AUC0-6)/MIC including the corresponding ratios based on calculated free-drug concentrations. This trial was registered at www.clinicaltrials.gov (NCT02042261).

Results

After 2 weeks of treatment, the median Chigh values for rifampicin, isoniazid, pyrazinamide and ethambutol were 10.0, 5.3, 41.1 and 3.3 mg/L respectively. Lower than recommended drug concentrations were detected in 42% of the patients for rifampicin (<8 mg/L), 19% for isoniazid (<3 mg/L), 27% for pyrazinamide (<35 mg/L) and 16% for ethambutol (<2 mg/L). The median Chigh/MIC values for rifampicin, isoniazid, pyrazinamide and ethambutol were 164, 128, 1.3 and 2.5, respectively, whereas the AUC0-6/MIC was 636 (range 156-2759) for rifampicin and 351 (range 72-895) for isoniazid.

Conclusions

We report low levels of first-line TB drugs in 16%-42% of patients, in particular for rifampicin. There was a wide distribution of the ratios between drug exposures and MICs. The future use of MIC determinations in TDM is dependent on the development of a reference method and clinically validated pharmacokinetic/pharmacodynamic targets.

Individualised dosing algorithm and personalised treatment of high-dose rifampicin for tuberculosis

AIMS

To propose new exposure targets for Bayesian dose optimisation suited for high-dose rifampicin and to apply them using measured plasma concentrations coupled with a Bayesian forecasting algorithm allowing predictions of future doses, considering rifampicin's auto-induction, saturable pharmacokinetics and high interoccasion variability.

METHODS

Rifampicin exposure targets for Bayesian dose optimisation were defined based on literature data on safety and anti-mycobacterial activity in relation to rifampicin's pharmacokinetics i.e. highest plasma concentration up to 24 hours and area under the plasma concentration-time curve up to 24 hours (AUC_0-24h ). Targets were suggested with and without considering minimum inhibitory concentration (MIC) information. Individual optimal doses were predicted for patients treated with rifampicin (10 mg/kg) using the targets with Bayesian forecasting together with sparse measurements of rifampicin plasma concentrations and baseline rifampicin MIC.

RESULTS

The suggested exposure target for Bayesian dose optimisation was a steady state AUC_0-24h of 181-214 h × mg/L. The observed MICs ranged from 0.016-0.125 mg/L (mode: 0.064 mg/L). The predicted optimal dose in patients using the suggested target ranged from 1200-3000 mg (20-50 mg/kg) with a mode of 1800 mg (30 mg/kg, n = 24). The predicted optimal doses when taking MIC into account were highly dependent on the known technical variability of measured individual MIC and the dose was substantially lower compared to when using the AUC_0-24h -only target.

CONCLUSIONS

A new up-to-date exposure target for Bayesian dose optimisation suited for high-dose rifampicin was derived. Using measured plasma concentrations coupled with Bayesian forecasting allowed prediction of the future dose whilst accounting for the auto-induction, saturable pharmacokinetics and high between-occasion variability of rifampicin.

Current research toward optimizing dosing of first-line antituberculosis treatment

Introduction: Drug concentrations in tuberculosis patients on standard regimens vary widely with clinically important consequences.

Areas covered: We review the available literature identifying factors correlated with pharmacokinetic variability of antituberculosis drugs. Based on population pharmacokinetic models and the weight, height, and sex distributions in a large data base of African tuberculosis patients, we propose simplified weight-based doses of the available fixed dose combination(FDC) for adults with drug susceptible tuberculosis. Emerging studies will support optimized weight-based dosing for children. Other sources of important pharmacokinetic variability include genetic variants, drug-drug interactions, formulation quality, and methods of preparation and administration.

Expert commentary: Optimized weight band-based dosing will result in more equitable distribution of drug exposures by weight. The use of high doses of isoniazid in patients with drug-resistant tuberculosis would be safer and more effective if a feasible test was developed to allow stratified dosing according to acetylator type. There is an urgent need for more suitable formulations of many second-line drugs for children. The adoption of new technologies and efficient FDC design may allow further advances for patients and treatment programs. Lastly, current efforts to ensure adequate quality of antituberculosis drug products are not preventing the use of substandard products to treat patients with tuberculosis.

Delayed Sputum Culture Conversion in Tuberculosis-Human Immunodeficiency Virus-Coinfected Patients With Low Isoniazid and Rifampicin Concentrations

Background

The relationship between concentrations of antituberculosis drugs, sputum culture conversion, and treatment outcome remains unclear. We sought to determine the association between antituberculosis drug concentrations and sputum conversion among patients coinfected with tuberculosis and human immunodeficiency virus (HIV) and receiving first-line antituberculosis drugs.

Methods

We enrolled HIV-infected Ugandans with pulmonary tuberculosis. Estimation of first-line antituberculosis drug concentrations was performed 1, 2, and 4 hours after drug intake at 2, 8, and 24 weeks of tuberculosis treatment. Serial sputum cultures were performed at each visit. Time-to-event analysis was used to determine factors associated with sputum culture conversion.

Results

We enrolled 268 HIV-infected patients. Patients with low isoniazid and rifampicin concentrations were less likely to have sputum culture conversion before the end of tuberculosis treatment (hazard ratio, 0.54; 95% confidence interval, .37-.77; P = .001) or by the end of follow-up (0.61; .44-.85; P = .003). Patients in the highest quartile for area under the rifampicin and isoniazid concentration-time curves for were twice as likely to experience sputum conversion than those in the lowest quartile. Rifampicin and isoniazid concentrations below the thresholds and weight <55 kg were both risk factors for unfavorable tuberculosis treatment outcomes. Only 4.4% of the participants had treatment failure.

Conclusion

Although low antituberculosis drug concentrations did not translate to a high proportion of patients with treatment failure, the association between low concentrations of rifampicin and isoniazid and delayed culture conversion may have implications for tuberculosis transmission. Clinical Trials Registration: NCT01782950.

Pharmacokinetics and pharmacogenetics of anti-tubercular drugs: a tool for treatment optimization?

INTRODUCTION

WHO global strategy is to end tuberculosis epidemic by 2035. Pharmacokinetic and pharmacogenetic studies are increasingly performed and might confirm their potential role in optimizing treatment outcome in specific settings and populations. Insufficient drug exposure seems to be a relevant factor in tuberculosis outcome and for the risk of phenotypic resistance. Areas covered: This review discusses available pharmacokinetic and pharmacogenetic data of first and second-line antitubercular agents in relation to efficacy and toxicity. Pharmacodynamic implications of optimized drugs and new options regimens are reviewed. Moreover a specific session describes innovative investigations on drug penetration. Expert opinion: The optimal use of available antitubercular drugs is paramount for tuberculosis control and eradication. Whilst trials are still on-going, higher rifampicin doses should be reserved to treatment for tubercular meningitis. Therapeutic Drug Monitoring with limiting sampling strategies is advised in patients at risk of failure or with slow treatment response. Further studies are needed in order to provide definitive recommendations of pharmacogenetic-based individualization: however lower isoniazid doses in NAT2 slow acetylators and higher rifampicin doses in individuals with SLCO1B1 loss of function genes are promising strategies. Finally in order to inform tailored strategies we need more data on tissue drug penetration and pharmacological modelling.

The utility of pharmacokinetic studies for the evaluation of exposure-response relationships for standard dose anti-tuberculosis drugs

Tuberculosis (TB) is a major public health problem. Many countries still fall below the minimum World Health Organization (WHO) TB treatment target success rate. There is conflicting evidence about whether concentrations of anti-tuberculosis drugs given at standard doses have an effect on treatment outcomes. The current data correlating anti-TB drug concentrations and treatment outcome is limited. This article summarized the existing literature and their utility in evaluating the association between each anti-TB drug's concentrations using current target concentrations and treatment outcomes in patients with pulmonary tuberculosis receiving standard WHO-recommended dosing.

Cohort profile of a study on outcomes related to tuberculosis and antiretroviral drug concentrations in Uganda: design, methods and patient characteristics of the SOUTH study

PURPOSE

Tuberculosis (TB) is a leading cause of death among people living with HIV in sub-Saharan Africa. Several factors influence the efficacy of TB treatment by leading to suboptimal drug concentrations and subsequently affecting treatment outcome. The aim of this cohort is to determine the association between anti-TB drug concentrations and TB treatment outcomes.

PARTICIPANTS

Patients diagnosed with new pulmonary TB at the integrated TB-HIV outpatient clinic in Kampala, Uganda, were enrolled into the study and started on first-line anti-TB treatment.

FINDINGS TO DATE

Between April 2013 and April 2015, the cohort enrolled 268 patients coinfected with TB/HIV ; 57.8% are male with a median age of 34 years (IQR 29-40). The median time between the diagnosis of HIV and the diagnosis of TB is 2 months (IQR 0-22.5). The majority of the patients are antiretroviral therapy naive (75.4%). Our population is severely immunosuppressed with a median CD4 cell count at enrolment of 163 cells/µL (IQR 46-298). Ninety-nine per cent of the patients had a diagnosis of pulmonary TB confirmed by sputum microscopy, Xpert/RIF or culture and 203 (75.7%) have completed TB treatment with 5099 aliquots of blood collected for pharmacokinetic analysis.

FUTURE PLANS

This cohort provides a large database of well-characterised patients coinfected with TB/HIV which will facilitate the description of the association between serum drug concentrations and TB treatment outcomes as well as provide a research platform for future substudies including evaluation of virological outcomes.

TRIAL REGISTRATION NUMBER

NCT01782950; Pre-results.

The importance of clinical pharmacokinetic-pharmacodynamic studies in unraveling the determinants of early and late tuberculosis outcomes

Tuberculosis remains a major infectious cause of morbidity and mortality worldwide. Current antibiotic regimens, constructed prior to the development of modern pharmacokinetic-pharmacodynamic (PK–PD) tools, are based on incomplete understanding of exposure–response relationships in drug susceptible and multidrug resistant tuberculosis. Preclinical and population PK data suggest that clinical PK–PD studies may enable therapeutic drug monitoring for some agents and revised dosing for others. Future clinical PK–PD challenges include: incorporation of PK methods to assay free concentrations for all active metabolites; selection of appropriate early outcome measures which reflect therapeutic response; elucidation of genetic contributors to interindividual PK variability; conduct of targeted studies on special populations (including children); and measurement of PK–PD parameters at the site of disease.

Factors Influencing Tuberculosis Treatment Outcome in Adult Patients Treated with Thrice-Weekly Regimens in India

The Indian Revised National Tuberculosis (TB) Control Programme uses thrice-weekly treatment with standard drug dosages. The role of plasma drug levels and other factors in determining TB treatment outcomes is not well understood. We aimed to determine the factors influencing the concentrations of rifampin (RMP), isoniazid (INH), and pyrazinamide (PZA) at 2 h postdosing in adult TB patients and to study the factors impacting TB treatment outcome. We recruited 1,912 adult TB patients (newly treated and retreated patients) with pulmonary/extrapulmonary TB receiving antitubercular treatment (ATT) in the RNTCP in Chennai, India. At steady state, the concentrations of RMP, INH, and PZA were determined at 2 h postdosing after supervised drug administration. A total of 1,648 patients had a favorable outcome, while 264 (14%) had an unfavorable outcome. A total of 91%, 16%, and 17% of the patients had suboptimal concentrations of RMP (<8 μg/ml), INH (<3 μg/ml), and PZA (<20 μg/ml), respectively. Factors associated with treatment outcome were low RMP concentrations (adjusted odds ratio [aOR], 0.94; 95% confidence interval [CI], 0.89 to 0.99; P = 0.036), category II ATT (aOR, 2.39; 95% CI, 1.56 to 3.65; P < 0.001), low body weight (aOR, 0.96; 95% CI, 0.94 to 0.98; P < 0.001), alcohol use (aOR, 2.17; 95% CI, 1.42 to 3.31; P < 0.001), male gender (aOR, 1.92; 95% CI, 1.02 to 3.62; P = 0.043), and baseline INH resistance (aOR, 5.74; 95% CI, 3.12 to 10.59; P < 0.001), which significantly increased the likelihood of an unfavorable outcome in multivariate logistic regression analysis. Further studies are needed to optimize anti-TB drug dosages and improve cure rates. Drug susceptibility testing at the baseline and attention to undernutrition and alcohol dependence are other important interventions.

Determination of plasma concentrations of levofloxacin by high performance liquid chromatography for use at a multidrug-resistant tuberculosis hospital in Tanzania

Therapeutic drug monitoring may improve multidrug-resistant tuberculosis (MDR-TB) treatment outcomes. Levofloxacin demonstrates significant individual pharmacokinetic variability. Thus, we sought to develop and validate a high-performance liquid chromatography (HPLC) method with ultraviolet (UV) detection for levofloxacin in patients on MDR-TB treatment. The HPLC-UV method is based on a solid phase extraction (SPE) and a direct injection into the HPLC system. The limit of quantification was 0.25 μg/mL, and the assay was linear over the concentration range of 0.25—15 μg/mL (y = 0.5668x—0.0603, R² = 0.9992) for the determination of levofloxacin in plasma. The HPLC-UV methodology achieved excellent accuracy and reproducibility along a clinically meaningful range. The intra-assay RSD% of low, medium, and high quality control samples (QC) were 1.93, 2.44, and 1.90, respectively, while the inter-assay RSD% were 3.74, 5.65, and 3.30, respectively. The mean recovery was 96.84%. This method was then utilized to measure levofloxacin concentrations from patients’ plasma samples from a retrospective cohort of consecutive enrolled subjects treated for MDR-TB at the national TB hospital in Tanzania during 5/3/2013–8/31/2015. Plasma was collected at 2 hours after levofloxacin administration, the time of estimated peak concentration (eC_max) treatment. Forty-one MDR-TB patients had plasma available and 39 had traceable programmatic outcomes. Only 13 (32%) patients had any plasma concentration that reached the lower range of the expected literature derived C_max with the median eC_max being 5.86 (3.33–9.08 μg/ml). Using Classification and Regression Tree analysis, an eC_max ≥7.55 μg/mL was identified as the threshold which best predicted cure. Analyzing this CART derived threshold on treatment outcome, the time to sputum culture conversion was 38.3 ± 22.7 days vs. 47.8 ± 26.5 days (p = 0.27) and a greater proportion were cured, in 10 out of 15 (66.7%) vs. 6 out of 18 (33.3%) (p = 0.06) respectively. Furthermore, one patient with an eC_max/minimum inhibitory concentration (MIC) of only 1.13 acquired extensively drug resistant (XDR)-TB while undergoing treatment. The individual variability of levofloxacin concentrations in MDR-TB patients from Tanzania supports further study of the application of onsite therapeutic drug monitoring and MIC testing.

The pharmacological challenges of treating tuberculosis and HIV coinfections

INTRODUCTION

Tuberculosis (TB) is the most prevalent opportunistic infection among HIV patients, and the leading cause of death among HIV patients worldwide. Simultaneous treatment of both diseases is recommended by current guidelines, but can be challenging due to the potential for drug-drug interactions, overlapping toxicities, difficulty adhering to medications, and an increased risk for immune reconstitution inflammatory syndrome (IRIS). Clinical manifestations of TB can also vary between HIV-infected patients and uninfected patients, which can increase the risk for delayed diagnosis. Areas covered: Topics covered in this review include the following: the inter-related pathophysiology of HIV and TB; clinical manifestations and diagnosis; drug-drug interactions, particularly the rifamycins with the antiretrovirals; IRIS presentation and treatment, as well as a discussion on overlapping toxicity between the two disease states. Expert commentary: The complexity of managing these two disease states simultaneously requires a multidisciplinary approach to care and dedicated resources. If properly funded, TB/HIV co-infection will continue to decline over the coming years.

Simultaneous quantification of isoniazid, rifampicin, ethambutol and pyrazinamide by liquid chromatography/tandem mass spectrometry

A remediable cause of poor treatment response in drug-susceptible tuberculosis (TB) patients may be low plasma levels of one or more of the first-line anti-TB drugs. The aim of this work was to develop an accurate and precise LC-MS/MS method for simultaneous quantification of all four first-line anti-TB drugs in plasma suitable for therapeutic drug monitoring (TDM). To adjust for degradation and losses during sample preparation, isotopically labeled compounds were used as internal standards. Plasma samples spiked with internal standards were extracted using protein precipitation with methanol and acetonitrile. Simultaneous separation of all four drugs was accomplished with a Chromolith Reversed-Phase column and mobile phases consisting of water, methanol, ammonium acetate and formic acid with subsequent mass spectrometric quantification. The linear range of the calibration curve for isoniazid was 0.5-10 mg/L, for rifampicin 0.75-30 mg/L, for ethambutol 0.25-10 mg/L and for pyrazinamide 4-80 mg/L. The lower limit of quantification was 0.5 mg/L, 0.75 mg/L, 0.25 mg/L and 4.0 mg/L, respectively. Precision estimated by the coefficient of variation was <15% for all four drugs. The LC-MS/MS method can readily be used for simultaneous quantification of first-line anti-TB drugs in plasma and is well suited for TDM.

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.

Naïve-pooled pharmacokinetic analysis of pyrazinamide, isoniazid and rifampicin in plasma and cerebrospinal fluid of Vietnamese children with tuberculous meningitis

BACKGROUND

Among the various forms of TB, tuberculous meningitis (TBM) is the most severe, with about 30% mortality and 50% of survivors left with neurological sequelae. Children suffer more frequently from TBM than adults and outcomes are often poor due to difficulties in making the diagnosis and uncertainty regarding the best anti-tuberculosis drug regimen. The aim of this prospective study was to describe the pharmacokinetics of pyrazinamide, isoniazid and rifampicin in plasma and cerebrospinal fluid of children with tuberculous meningitis treated with the standard TBM regimen.

METHODS

We performed a prospective observational study of 100 consecutively treated children (≤ 15 years of age) with tuberculous meningitis in Ho Chi Minh City, Vietnam. Children were treated according to the 2006 WHO recommended pediatric treatment regimen consisting of isoniazid (5 mg/kg), rifampicin (10 mg/kg) and ethambutol (15 mg/kg) for 8 months, with the addition of pyrazinamide (25 mg/kg) for the first 3 months and streptomycin (15 mg/kg) for the first 2 months. Pyrazinamide, isoniazid and rifampicin concentrations were measured in plasma at day 14 and in cerebrospinal fluid (CSF) at 1 month by HPLC-UV. A naïve-pooled non-compartmental data analysis was used to describe the pharmacokinetic properties of drugs in the two-age groups of children ≤ 4 years or > 4 years of age.

RESULTS

Younger children, when compared to older children, presented a higher body weight-normalized clearance and volume of distribution, and lower median total plasma exposures for the three studied drugs with -14%, -22% and -16% for Pyrazinamide, Isoniazid and Rifampicin, respectively. In CSF, individual concentrations of isoniazid and pyrazinamide were comparable to that in plasma in both age groups; but rifampicin concentrations were lower than the minimum inhibitory concentration of susceptible bacteria in all but two children.

CONCLUSIONS

There is an age-dependent variation in the plasma and cerebrospinal fluid pharmacokinetics of rifampicin, isoniazid and pyrazinamide. The safety and efficacy of higher doses of rifampicin should be investigated for the treatment of childhood tuberculous meningitis.

Therapeutic drug monitoring of antimicrobials

As pathology services become more centralized and automated, the measurement of therapeutic antimicrobial drugs concentrations is increasingly performed in clinical biochemistry or 'blood science' laboratories. This review outlines key groups of antimicrobial agents: aminoglycosides, glycopeptides, antifungal agents and antituberculosis agents, their role in managing infectious diseases, and the reasons why serum concentration measurement is important.

Serum Levels of Antituberculosis Drugs and Their Effect on Tuberculosis Treatment Outcome

Therapeutic drug monitoring in tuberculosis remains controversial. We evaluated the relationship between antituberculosis drug levels in blood and clinical outcome. Serum concentrations of first-line antituberculosis drugs were measured in tuberculosis patients between March 2006 and April 2013. Venous blood was drawn 2 h after drug ingestion and was analyzed using high-performance liquid chromatography-tandem mass spectrometry. We retrospectively reviewed the data and determined the association of serum drug levels with clinical outcome. Among 413 patients, the prevalences of low serum concentrations of isoniazid (INH), rifampin (RMP), ethambutol (EMB), and pyrazinamide (PZA) were 59.9%, 27.8%, 12.8%, and 8.7%, respectively. The low INH group had a greater percentage of patients with a history of tuberculosis treatment (19.2% versus 11.0%; P = 0.026) and was more likely to present with drug-resistant strains (17.6% versus 8.8%; P = 0.049) than the normal INH group; however, low levels of INH, RMP, EMB, and PZA were not related to treatment outcome. Low INH level had a tendency to be associated with 2-month culture positivity, but it was not statistically significant (P = 0.072) in multivariate analysis. Seventeen (4.1%) patients experienced a recurrence. However, the recurrence rate was not statistically different between the low and normal INH groups. Low serum INH may play a role in recurrence and in acquired drug resistance. However, the serum level of INH was not directly related to either treatment response or recurrence rate. The role and usefulness of therapeutic drug monitoring should be evaluated in further prospective studies.

Pharmacokinetic Modeling and Optimal Sampling Strategies for Therapeutic Drug Monitoring of Rifampin in Patients with Tuberculosis

Rifampin, together with isoniazid, has been the backbone of the current first-line treatment of tuberculosis (TB). The ratio of the area under the concentration-time curve from 0 to 24 h (AUC0-24) to the MIC is the best predictive pharmacokinetic-pharmacodynamic parameter for determinations of efficacy. The objective of this study was to develop an optimal sampling procedure based on population pharmacokinetics to predict AUC0-24 values. Patients received rifampin orally once daily as part of their anti-TB treatment. A one-compartmental pharmacokinetic population model with first-order absorption and lag time was developed using observed rifampin plasma concentrations from 55 patients. The population pharmacokinetic model was developed using an iterative two-stage Bayesian procedure and was cross-validated. Optimal sampling strategies were calculated using Monte Carlo simulation (n = 1,000). The geometric mean AUC0-24 value was 41.5 (range, 13.5 to 117) mg · h/liter. The median time to maximum concentration of drug in serum (Tmax) was 2.2 h, ranging from 0.4 to 5.7 h. This wide range indicates that obtaining a concentration level at 2 h (C2) would not capture the peak concentration in a large proportion of the population. Optimal sampling using concentrations at 1, 3, and 8 h postdosing was considered clinically suitable with an r(2) value of 0.96, a root mean squared error value of 13.2%, and a prediction bias value of -0.4%. This study showed that the rifampin AUC0-24 in TB patients can be predicted with acceptable accuracy and precision using the developed population pharmacokinetic model with optimal sampling at time points 1, 3, and 8 h.