Therapeutic drug monitoring in the treatment of active tuberculosis

Precision Medicine Strategies to Improve Isoniazid Therapy in Patients with Tuberculosis

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

Therapeutic drug monitoring in India: A strength, weakness, opportunity and threats analysis

Over the last three to four decades, Therapeutic Drug Monitoring (TDM) has shaped itself as therapeutic drug management, an integral component of precision medicine. The practice of TDM is not extensive in India, despite being one of the fastest-growing economies in the world. It is currently limited to a few academic medical centres and teaching hospitals. Apart from the immunosuppressive drugs, several other therapeutic areas, such as anticancer, antifungal, antibiotic and antitubercular, have demonstrated great potential to improve patient outcomes in Indian settings. Factors such as the higher prevalence of nutritional deficiencies, tropical diseases, widespread use of alternative medicines, unalike pharmacogenomics and sparse population-specific data available on therapeutic ranges of several drugs make the population of this subcontinent unique regarding the relevance of TDM. Despite the impact of TDM in clinical science and its widespread application, TDM has failed to receive the attention it deserves in India. This review intends to bring out a strength, weakness, opportunity and threats (SWOT) analysis for TDM in India so that appropriate steps for fostering the growth of TDM could be envisioned. The need of the hour is the creation of a cooperative group including all the stakeholders, such as TDM professionals, clinicians and the government and devising a National Action Plan to strengthen TDM. Nodal TDM centres should be established, and pilot programmes should be rolled out to identify the thrust areas for TDM in the country, capacity building and creating awareness to integrate TDM into mainstream clinical medicine.

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.

Human Cytochrome P450 1, 2, 3 Families as Pharmacogenes with Emphases on Their Antimalarial and Antituberculosis Drugs and Prevalent African Alleles

Precision medicine gives individuals tailored medical treatment, with the genotype determining the therapeutic strategy, the appropriate dosage, and the likelihood of benefit or toxicity. Cytochrome P450 (CYP) enzyme families 1, 2, and 3 play a pivotal role in eliminating most drugs. Factors that affect CYP function and expression have a major impact on treatment outcomes. Therefore, polymorphisms of these enzymes result in alleles with diverse enzymatic activity and drug metabolism phenotypes. Africa has the highest CYP genetic diversity and also the highest burden of malaria and tuberculosis, and this review presents current general information on CYP enzymes together with variation data concerning antimalarial and antituberculosis drugs, while focusing on the first three CYP families. Afrocentric alleles such as CYP2A6*17, CYP2A6*23, CYP2A6*25, CYP2A6*28, CYP2B6*6, CYP2B6*18, CYP2C8*2, CYP2C9*5, CYP2C9*8, CYP2C9*9, CYP2C19*9, CYP2C19*13, CYP2C19*15, CYP2D6*2, CYP2D6*17, CYP2D6*29, and CYP3A4*15 are implicated in diverse metabolic phenotypes of different antimalarials such as artesunate, mefloquine, quinine, primaquine, and chloroquine. Moreover, CYP3A4, CYP1A1, CYP2C8, CYP2C18, CYP2C19, CYP2J2, and CYP1B1 are implicated in the metabolism of some second-line antituberculosis drugs such as bedaquiline and linezolid. Drug-drug interactions, induction/inhibition, and enzyme polymorphisms that influence the metabolism of antituberculosis, antimalarial, and other drugs, are explored. Moreover, a mapping of Afrocentric missense mutations to CYP structures and a documentation of their known effects provided structural insights, as understanding the mechanism of action of these enzymes and how the different alleles influence enzyme function is invaluable to the advancement of precision medicine.

The impact of enteral feeding and therapeutic monitoring of rifampicin with dose escalation in critically ill patients with tuberculosis

OBJECTIVES

Critically ill patients with tuberculosis (TB) face a high mortality risk and require effective treatment. There is a paucity of data on rifampicin pharmacokinetics, the impact of continuous enteral feeding on drug absorption, and the potential of therapeutic drug monitoring (TDM) to optimize drug exposure in these patients.

METHODS

We performed a sequential pharmacokinetic study to determine the impact of feeding and TDM with rifampicin dose escalation in critically ill patients with TB. Noncompartmental pharmacokinetic analysis was performed.

RESULTS

Among 20 critically ill patients (40% were HIV-infected), median rifampicin Cmax (maximum serum concentration) in the fasted and fed states were 5.1 µg/ml versus 3.3 µg/ml, respectively (P <0.0001; geometric mean ratio 1.95; 90% confidence interval 1.46-2.60). The proportion of patients with low rifampicin concentrations in the fasted and fed states was 80% vs 100% (P-value = 0.1336). Optimized dosing led to a per-patient median rifampicin dosing of 24.6 mg/kg and a median Cmax increase from 2.4 µg/ml to 17.8 µg/ml (P-value = 0.0005; geometric mean ratio 8.29; 90% confidence interval 3.88-17.74). TDM-guided dose escalation increased the proportion of patients achieving the suggested target rifampicin concentration compared with standard dosing (83% vs 0%, P-value = 0.004).

CONCLUSION

We found low rifampicin concentrations in all patients receiving continuous enteral feeding. TDM-guided dose escalation provided an effective strategy to achieve target drug exposure in these critically ill patients with TB.

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.

Simultaneous determination of first-line anti-tuberculosis drugs and one metabolite of isoniazid by liquid chromatography/tandem mass spectrometry in patients with human immunodeficiency virus-tuberculosis coinfection

The incidence rate of tuberculosis (TB) in patients with human immunodeficiency virus (HIV) infection is 26 times higher than that in other patients. Patients with both infections require long-term combination therapy, which increases therapy complexity and might lead to serious adverse reactions and drug-drug interactions. To optimize therapy for patients with HIV and TB coinfection, we developed an ultra-high-performance liquid chromatography/tandem mass spectrometry (UHPLC-MS/MS) method to simultaneously quantify four anti-tuberculosis drugs and one isoniazid (INH) metabolite. Blood samples (n = 32) from 16 patients with HIV and TB coinfection were collected. Plasma protein precipitation with acetonitrile was followed by a hydrazine reaction between INH and cinnamaldehyde (CA) to produce phenylhydrazone (CA-INH) and dilution with heptafluorobutyric acid. The separation was performed on an Acquity UHPLC HSS T3 1.8 μm column (2.1 × 100 mm, Waters) with a mobile phase consisting of 10 mmol/L ammonium formate (pH = 4) in water (solvent A) and 0.1 % formic acid in methanol (solvent B) in a gradient elution. The compounds were detected using a positive multiple reaction monitoring model. INH, acetyl-INH (AC-INH), rifampicin (RIF), ethambutol (EMB), and pyrazinamide (PZA) showed good linear relationships in their quantitative ranges, with lower limits of quantification of 48, 192, 200, 96, and 480 ng/mL, respectively. The inter- and intraday precision was within 15 %, and the accuracy was between 85 % and 115 %. The mean plasma concentrations of INH, AC-INH, RIF, EMB, and PZA in patients were 1990.23 (24–16 600), 863.06 (96–2880), 3507.05 (229–9800), 808.10 (149–2130), and 18 838.33 (240–34 800) ng/mL, respectively. The plasma concentrations detected in the 16 patients were lower than the targeted concentrations in HIV-negative TB patients. In summary, we developed a simple UHPLC-MS/MS method for simultaneous quantification of first-line TB drugs, and successfully applied it for therapeutic drug monitoring in patients with HIV and TB coinfection. This method will facilitate monitoring of TB drugs in the future.

Too Much of a Good Thing: Defining Antimicrobial Therapeutic Targets to Minimize Toxicity

Antimicrobials are a common cause of drug toxicity. Understanding the relationship between systemic antimicrobial exposure and toxicity is necessary to enable providers to take a proactive approach to prevent undesired drug effects. When an exposure threshold has been defined that predicts drug toxicity, therapeutic drug monitoring (TDM) can be performed to assure drug exposure does not exceed the defined threshold. Although some antimicrobials have well-defined dose-dependent toxicities, many other exposure-toxicity relationships have either not been well-defined or, in some cases, not been evaluated at all. In this review, we examine the relationship between exposures and toxicities for antibiotic, antifungal, and antiviral agents. Furthermore, we classify these relationships into four categories: known association between drug exposure and toxicity such that clinical implementation of a specific exposure threshold associated with toxicity for TDM is supported (category 1), known association between drug exposure and toxicity but the specific exposure threshold associated with toxicity is undefined (category 2), association between drug exposure and toxicity has been suggested but relationship is poorly defined (category 3), and no known association between drug exposure and toxicity (category 4). Further work to define exposure-toxicity thresholds and integrate effective TDM strategies has the potential to minimize many of the observed antimicrobial toxicities.

Isoniazid Therapeutic Drug Monitoring in Tunisian Patients With Tuberculosis

A regular therapeutic drug monitoring (TDM) of isoniazid could be useful to predict the acetylation profile and to prescribe doses associated with optimal efficacy and safety. We aimed to assess the usefulness of isoniazid TDM in the Tunisian population, to describe the acetylation profile distribution in this population, and to investigate the influence of certain parameters on acetylation phenotype. We performed a retrospective study including Tunisian patients with tuberculosis underwent an isoniazid TDM. Isoniazid concentrations were measured 3 hours after drug intake (C₃ ). Subsequent isoniazid doses were adjusted to maintain the C₃ within the recommended target (1-2 µg/mL). Patients were qualified as slow acetylators (SAs) or rapid acetylators (RAs) according to their acetylation index. Among the 255 patients, 58% were SAs and 42% were RAs. Of all patients, only 30.6% had a C₃ value within the target range. A dose adjustment has been performed for patients with C₃ outside the target range. C₃ was controlled in 77 patients. It became within the target range in 39 patients (50.6%). The median recommended isoniazid weight doses for SAs and RAs were 2.1 ± 0.7 mg/kg and 4.2 ± 1.4 mg/kg, respectively. The multivariate analysis showed that body weight, C_3, and C₃ /isoniazid dose were found to be significantly different between the 2 acetylation groups. In the pediatric group, only 9 had a C₃ value within the target range, and all of them were RAs. The irrevocable interest of isoniazid TDM has been shown in Tunisian patients with tuberculosis, in both adult and pediatric patients, as isoniazid demonstrates an unpredictable pharmacokinetic profile.

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.

Rapid and simultaneous determination of ten anti-tuberculosis drugs in human plasma by UPLC-MS/MS with applications in therapeutic drug monitoring

Tuberculosis remains a global challenge, particularly with a growing number of resistant cases, which may become an obstacle to eliminating this disease. Standardized short-course therapy composed of first-line anti-tuberculosis drugs isoniazid (INH), rifampicin (RIF), ethambutol (EMB), and pyrazinamide (PZA) is playing vital roles for curbing the rapid spread of tuberculosis. However, some patients have poor responses to standardized short-course therapy. As the number of drug-resistant tuberculosis increase, some other anti-tuberculous drugs are needed to achieve better treatment outcomes. In this study, we established a UPLC-MS/MS method for simultaneous detection of ten anti-tuberculosis drugs in human plasma including INH, EMB, PZA, RIF, rifampin, rifapentine as well as four second-line antituberculosis drugs, i.e. ethionamide, protionamide, thiosemicarbazone and clofazimine. This study contains almost all the commonly used anti-tuberculosis drugs. The plasma samples were treated with acetonitrile to precipitate proteins, and doped with the isotope internal standard. A Shiseido CAPCELL RAK-ADME (2.1 mm × 50 mm, 3 μm) column was used for chromatographic separation, and acetonitrile-water (containing 0.1% formic acid) was the mobile phase. The separation used gradient elution with a flow rate of 0.4 mL/min. The column temperature was 40 °C, and the sample volume was 1 μL. The electrospray ionization source (ESI) and the positive ion multiple reaction monitoring (MRM) mode were used for the detection. The analysis time was as short as 7 min. The results show a good linear relationship under optimized conditions in the range of 5.00-7.50 × 10³, 1.00-1.50 × 10³, 5.00-5.00 × 10⁴, 5.00-7.50 × 10³, 1.00-3.00 × 10³, 1.00 × 10¹-1.00 × 10⁴, 1.00-3.00 × 10³, 1.00-3.00 × 10³, 2.00-4.00 × 10³, and 1.00 × 10^-1-2.00 × 10² ng/mL for INH, EMB PZA, RIF, rifabutin, rifapentine, ethionamide, protionamide, thiosemicarbazone, and clofazimine, respectively, with a linear correlation coefficient of R > 0.99. Finally, 34 patients with pulmonary TB were tested for therapeutic drug monitoring. The results showed that the presented method have significant advances in sensitivity, separation efficiency and simplicity.

Pharmacokinetic study of two different rifabutin doses co-administered with lopinavir/ritonavir in African HIV and tuberculosis co-infected adult patients

Background

This study aimed to assess the pharmacokinetic profile of 150 mg rifabutin (RBT) taken every other day (every 48 h) versus 300 mg RBT taken every other day (E.O.D), both in combination with lopinavir/ritonavir (LPV/r), in adult patients with human immunodeficiency virus (HIV) and tuberculosis (TB) co-infection.

Methods

This is a two-arm, open-label, pharmacokinetic, randomised study conducted in Burkina Faso between May 2013 and December 2015. Enrolled patients were randomised to receive either 150 mg RBT EOD (arm A, 9 subjects) or 300 mg RBT EOD (arm B, 7 subjects), both associated with LPV/r taken twice daily. RBT plasma concentrations were evaluated after 2 weeks of combined HIV and TB treatment. Samples were collected just before drug ingestion and at 1, 2, 3, 4, 6, 8, and 12 h after drug ingestion to measure plasma drug concentration using an HPLC-MS/MS assay.

Results

The Cmax and AUC_0–12h medians in arm A (Cmax = 296 ng/mL, IQR: 205–45; AUC_0–12h = 2528 ng.h/mL, IQR: 1684–2735) were lower than those in arm B (Cmax = 600 ng/mL, IQR: 403–717; AUC_0–12h = 4042.5 ng.h/mL, IQR: 3469–5761), with a statistically significant difference in AUC_0–12h (p = 0.044) but not in Cmax (p = 0.313). No significant differences were observed in Tmax (3 h versus 4 h). Five patients had a Cmax below the plasma therapeutic limit (< 300 ng/mL) in the 150 mg RBT arm, while the Cmax was above this threshold for all patients in the 300 mg RBT arm. Additionally, at 48 h after drug ingestion, all patients had a mycobacterial minimum inhibitory concentration (MIC) above the limit (> 64 ng/mL) in the 300 mg RBT arm, while 4/9 patients had such values in the 150 mg RBT arm.

Conclusion

This study confirmed that the 150 mg dose of rifabutin ingested EOD in combination with LPV/r is inadequate and could lead to selection of rifamycin-resistant mycobacteria.

Trial registration

PACTR201310000629390, 28th October 2013.

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 systematic review and meta-analysis of first-line tuberculosis drug concentrations and treatment outcomes

Low serum concentrations of first-line tuberculosis (TB) drugs have been widely reported. However, the impact of low serum concentrations on treatment outcome is less well studied. A systematic search of MEDLINE/Pubmed and the Cochrane Central Register of Controlled Trials up to 31 March 2018 was conducted for articles describing drug concentrations of first-line TB drugs and treatment outcome in adult patients with drug-susceptible TB. The search identified 3073 unique publication abstracts, which were reviewed for suitability: 21 articles were acceptable for inclusion in the qualitative analysis comprising 13 prospective observational cohorts, 4 retrospective observational cohorts, 1 case-control study and 3 randomised controlled trials. Data for meta-analysis were available for 15 studies, 13 studies of rifampicin (RMP), 10 of isoniazid (INH), 8 of pyrazinamide (PZA) and 4 of ethambutol (EMB). This meta-analysis revealed that low PZA concentration appears to increase the risk of poor outcomes (8 studies, n = 2727; RR 1.73, 95%CI 1.10-2.72), low RMP concentrations may slightly increase the risk of poor outcomes (13 studies, n = 2753; RR 1.40, 95%CI 0.91-2.16), whereas low concentrations of INH (10 studies, n = 2640; RR 1.32, 95%CI 0.66-2.63) and EMB (4 studies, n = 551; RR 1.12, 95%CI 0.41-3.05) appear to make no difference to treatment outcome. There was no significant publication bias or between-study heterogeneity in any of the analyses. The potential clinical impact of low concentrations of PZA and RMP warrants further evaluation. Also, comprehensive assessments of the complex pharmacokinetic-pharmacodynamic relationships in the treatment of TB are urgently needed.

Pharmacokinetics of rifampicin in adult TB patients and healthy volunteers: a systematic review and meta-analysis

Objectives

The objectives of this study were to explore inter-study heterogeneity in the pharmacokinetics (PK) of orally administered rifampicin, to derive summary estimates of rifampicin PK parameters at standard dosages and to compare these with summary estimates for higher dosages.

Methods

A systematic search was performed for studies of rifampicin PK published in the English language up to May 2017. Data describing the C_max and AUC were extracted. Meta-analysis provided summary estimates for PK parameter estimates at standard rifampicin dosages. Heterogeneity was assessed by estimation of the I² statistic and visual inspection of forest plots. Summary AUC estimates at standard and higher dosages were compared graphically and contextualized using preclinical pharmacodynamic (PD) data.

Results

Substantial heterogeneity in PK parameters was evident and upheld in meta-regression. Treatment duration had a significant impact on the summary estimates for rifampicin PK parameters, with C_max 8.98 mg/L (SEM 2.19) after a single dose and 5.79 mg/L (SEM 2.14) at steady-state dosing, and AUC 72.56 mg·h/L (SEM 2.60) and 38.73 mg·h/L (SEM 4.33) after single and steady-state dosing, respectively. Rifampicin dosages of at least 25 mg/kg are required to achieve plasma PK/PD targets defined in preclinical studies.

Conclusions

Vast inter-study heterogeneity exists in rifampicin PK parameter estimates. This is not explained by the available modifying variables. The recommended dosage of rifampicin should be increased to improve efficacy. This study provides an important point of reference for understanding rifampicin PK at standard dosages as efforts to explore higher dosing strategies continue in this field.

Historical BCG vaccination combined with drug treatment enhances inhibition of mycobacterial growth ex vivo in human peripheral blood cells

Tuberculosis (TB) is a leading infectious cause of death globally. Drug treatment and vaccination, in particular with Bacillus Calmette-Guérin (BCG), remain the main strategies to control TB. With the emergence of drug resistance, it has been proposed that a combination of TB vaccination with pharmacological treatment may provide a greater therapeutic value. We implemented an ex vivo mycobacterial growth inhibition assay (MGIA) to discriminate vaccine responses in historically BCG-vaccinated human volunteers and to assess the contribution of vaccine-mediated immune response towards the killing effect of mycobacteria in the presence of the antibiotics isoniazid (INH) and rifampicin (RIF), in an attempt to develop the assay as a screening tool for therapeutic TB vaccines. BCG vaccination significantly enhanced the ability of INH to control mycobacterial growth ex vivo. The BCG-vaccinated group displayed a higher production of IFN-γ and IP-10 when peripheral blood mononuclear cells (PBMC) were co-cultured with INH, with a similar trend during co-culture with RIF. A higher frequency of IFN-γ+ and TNF-α+ CD3- CD4- CD8- cells was observed, suggesting the contribution of Natural Killer (NK) cells in the combined effect between BCG vaccination and INH. Taken together, our data indicate the efficacy of INH can be augmented following historical BCG vaccination, which support findings from previous observational and animal studies.

Matryoshka-type gastro-resistant microparticles for the oral treatment of Mycobacterium tuberculosis

AIM

Production of Matryoshka-type gastroresistant microparticles containing antibiotic-loaded poly lactic-co-glycolic acid (PLGA) nanoparticles (NP) against Mycobacterium tuberculosis.

MATERIALS & METHODS

The emulsification and evaporation methods were followed for the synthesis of PLGA-NPs and methacrylic acid-ethyl acrylate-based coatings to protect rifampicin from degradation under simulated gastric conditions.

RESULTS & CONCLUSION

The inner antibiotic-loaded NPs here reported can be released under simulated intestinal conditions whereas their coating protects them from degradation under simulated gastric conditions. The encapsulation does not hinder the antituberculosis action of the encapsulated antibiotic rifampicin. A sustained antibiotic release could be obtained when using the drug-loaded encapsulated NPs. Compared with the administration of the free drug, a more effective elimination of M. tuberculosis was observed when applying the NPs against infected macrophages. The antibiotic-loaded PLGA-NPs were also able to cross an in vitro model of intestinal barrier.

Bacterial Factors That Predict Relapse after Tuberculosis Therapy

BACKGROUND

Approximately 5% of patients with drug-susceptible tuberculosis have a relapse after 6 months of first-line therapy, as do approximately 20% of patients after 4 months of short-course therapy. We postulated that by analyzing pretreatment isolates of Mycobacterium tuberculosis obtained from patients who subsequently had a relapse or were cured, we could determine any correlations between the minimum inhibitory concentration (MIC) of a drug below the standard resistance breakpoint and the relapse risk after treatment.

METHODS

Using data from the Tuberculosis Trials Consortium Study 22 (development cohort), we assessed relapse and cure isolates to determine the MIC values of isoniazid and rifampin that were below the standard resistance breakpoint (0.1 μg per milliliter for isoniazid and 1.0 μg per milliliter for rifampin). We combined this analysis with clinical, radiologic, and laboratory data to generate predictive relapse models, which we validated by analyzing data from the DMID 01-009 study (validation cohort).

RESULTS

In the development cohort, the mean (±SD) MIC of isoniazid below the breakpoint was 0.0334±0.0085 μg per milliliter in the relapse group and 0.0286±0.0092 μg per milliliter in the cure group, which represented a higher value in the relapse group by a factor of 1.17 (P=0.02). The corresponding MIC values of rifampin were 0.0695±0.0276 and 0.0453±0.0223 μg per milliliter, respectively, which represented a higher value in the relapse group by a factor of 1.53 (P<0.001). Higher MIC values remained associated with relapse in a multivariable analysis that included other significant between-group differences. In an analysis of receiver-operating-characteristic curves of relapse based on these MIC values, the area under the curve (AUC) was 0.779. In the development cohort, the AUC in a multivariable model that included MIC values was 0.875. In the validation cohort, the MIC values either alone or combined with other patient characteristics were also predictive of relapse, with AUC values of 0.964 and 0.929, respectively. The use of a model score for the MIC values of isoniazid and rifampin to achieve 75.0% sensitivity in cross-validation analysis predicted relapse with a specificity of 76.5% in the development cohort and a sensitivity of 70.0% and a specificity of 100% in the validation cohort.

CONCLUSIONS

In pretreatment isolates of M. tuberculosis with decrements of MIC values of isoniazid or rifampin below standard resistance breakpoints, higher MIC values were associated with a greater risk of relapse than lower MIC values. (Funded by the National Institute of Allergy and Infectious Diseases.).

Effect of rifampin with bio-enhancer in the treatment of newly diagnosed sputum positive pulmonary tuberculosis patients: A double-center study

Objective

To compare a fixed-dose combination (FDC) of Rifampicin 450 mg, Isoniazid 300 mg, Pyrazinamide 1500 mg and Ethambutol 800 mg (usual care group) and regimen of Rifampicin 200 mg, Isoniazid 300 mg and piperine 10 mg along with Pyrazinamide 1500 mg and Ethambutol 800 mg (intervention care group).

Methods

A randomized, prospective, parallel group study was conducted on newly diagnosed tuberculosis patients. The drugs were given during intensive and continuous phase of treatment to newly diagnosed sputum positive pulmonary tuberculosis. All the patients were subjected to sputum examination, biochemical investigations followed by adverse drug event (ADE) monitoring.

Results

A total of 63 patients completed the study. No significant difference was observed in baseline characteristics of patients between the study groups. At the end of the continuous phase, both the groups showed zero bacteria detection. However, in the intervention group, the rate of sputum conversion was much faster than the usual care group. The rate of increase in SGOT and SGPT was much higher in the usual care group (p < 0.0001) than the interventional group (p < 0.05). Urea and creatinine has also increased from pre-treatment to end visit. The number of patients reported ADEs was less in the intervention care group (22.22%) when compared to the usual care group (36.84%).

Conclusion

Rifampicin 200 mg with piperine 10 mg FDC is compatible with the usual CAT-1 regimen.

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.

Therapeutic drug monitoring of antitubercular agents for disseminated Mycobacterium tuberculosis during intermittent haemodialysis and continuous venovenous haemofiltration

WHAT IS KNOWN AND OBJECTIVE

There is a lack of data regarding therapeutic drug monitoring (TDM) of antitubercular agents in the setting of continuous venovenous haemofiltration (CVVH). We describe TDM results of numerous antitubercular agents in a critically ill patient during CVVH and haemodialysis.

CASE SUMMARY

A 49-year-old man was initiated on treatment for disseminated Mycobacterium tuberculosis. During hospital admission, the patient developed critical illness and required renal replacement therapy. TDM results and pharmacokinetic calculations showed adequate serum concentrations of rifampin, ethambutol and amikacin during CVVH and of rifampin, pyrazinamide, ethambutol and levofloxacin during intermittent haemodialysis.

WHAT IS NEW AND CONCLUSION

The presence of critical illness and renal replacement therapy can induce pharmacokinetic changes that may warrant vigilant TDM to ensure optimal therapy. To our knowledge, this is the first report to describe TDM for several antitubercular agents during CVVH in a critically patient with disseminated M. tuberculosis.

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.

Population pharmacokinetics of rifampicin in adult patients with osteoarticular infections: interaction with fusidic acid

AIMS

Rifampicin represents the key antibiotic for the management of osteoarticular infections. An important pharmacokinetic variability has already been described, particularly for absorption and metabolism. All previous pharmacokinetic studies have been focused only on patients treated for tuberculosis. The objective of the present study was to describe a population pharmacokinetic model of rifampicin in patients with staphylococcal osteoarticular infections, which has not been investigated to date.

METHOD

Rifampicin concentrations were collected retrospectively from 62 patients treated with oral rifampicin 300 mg three times daily. Plasma concentration-time data were analysed using NONMEM to estimate population pharmacokinetic parameters. Demographic data, infection characteristics and antibiotics taken in addition to rifampicin antibiotics were investigated as covariates.

RESULTS

A one-compartment model, coupled to a transit absorption model, best described the rifampicin data. Fusidic acid coadministration was identified as a covariate in rifampicin pharmacokinetic parameters. The apparent clearance and apparent central volume of distribution mean values [95% confidence interval (CI)] were 5.1 1 h^-1 (1.2, 8.2 1 h^-1 )/23.8 l (8.9, 38.7 l) and 13.7 1 h^-1 (10.6, 18.0 1 h^-1 )/61.1 1 (40.8, 129.0 1) for patients with and without administration of fusidic acid, respectively. Interindividual variability (95% CI) in the apparent clearance and apparent central volume of distribution were 72.9% (49.5, 86.0%) and 59.1% (5.5, 105.4%), respectively. Residual variability was 2.3 mg l^-1 (1.6, 2.6 mg l^-1 ).

CONCLUSION

We developed the first population pharmacokinetic model of rifampicin in patients with osteoarticular infections. Our model demonstrated that fusidic acid affects rifampicin pharmacokinetics, leading to potential high drug exposure. This finding suggests that fusidic acid dosing regimens should be reconsidered.

Bioanalysis of antitubercular drugs using liquid chromatography

Tuberculosis is a life threatening disease and second to HIV in terms of deaths due to infectious diseases. Drug resistance development of the first-line drugs is a major concern in the treatment of this disease. There is no comprehensive and critical review in the literature of the bioanalytical methods for the determination of anti-tubercular agents from last two decades. This work offers a detailed account on the liquid chromatographic methods reported in the literature for the estimation of various anti-tubercular drugs. Major emphasis is given to sample preparation process, sensitivity of method, chromatographic separation conditions and detection systems used in their bioanalysis.

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.

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.

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.

A proposal for an individualized pharmacogenetic-guided isoniazid dosage regimen for patients with tuberculosis

BACKGROUND/AIM

Isoniazid (INH) is an essential component of first-line anti-tuberculosis (TB) treatment. However, treatment with INH is complicated by polymorphisms in the expression of the enzyme system primarily responsible for its elimination, N-acetyltransferase 2 (NAT2), and its associated hepatotoxicity. The objective of this study was to develop an individualized INH dosing regimen using a pharmacogenetic-driven model and to apply this regimen in a pilot study.

METHODS

A total of 206 patients with TB who received anti-TB treatment were included in this prospective study. The 2-hour post-dose concentrations of INH were obtained, and their NAT2 genotype was determined using polymerase chain reaction and sequencing. A multivariate regression analysis that included the variables of age, sex, body weight, and NAT2 genotype was performed to determine the best model for estimating the INH dose that achieves a concentration of 3.0-6.0 mg/L. This dosing algorithm was then used for newly enrolled 53 patients.

RESULTS

Serum concentrations of INH were significantly lower in the rapid-acetylators than in the slow-acetylators (2.55 mg/L vs 6.78 mg/L, median, P<0.001). A multivariate stepwise linear regression analysis revealed that NAT2 and body weight independently affected INH concentrations: INH concentration (mg/L) = 13.821-0.1× (body weight, kg) -2.273× (number of high activity alleles of NAT2; 0, 1, 2). In 53 newly enrolled patients, the frequency at which they were within the therapeutic range of 3.0-6.0 mg/L was higher in the model-based treatment group compared to the standard treatment group (80.8% vs 59.3%).

CONCLUSION

The use of individualized pharmacogenetic-guided INH dosage regimens that incorporate NAT2 genotype and body weight may help to ensure achievement of therapeutic concentrations of INH in the TB patients.

Limited sampling strategies to predict the area under the concentration-time curve for rifampicin

BACKGROUND

Rifampicin (RMP) is the most effective first-line antituberculosis drug. One of the most critical aspects of using it in fixed-drug combination formulations is to ensure it reaches therapeutic levels in blood. The determination of the area under the concentration-time curve (AUC) and appropriate dose adjustment of this drug may contribute to optimization of therapy. Even when the maximal concentration (Cmax) of RMP also predicts its sterilizing effect, the time to reach it (Tmax) takes 40 minutes to 6 hours. The aim of this study was to develop a limited sampling strategy (LSS) for therapeutic drug monitoring assistance for RMP.

METHODS

Full concentration-time curves were obtained from 58 patients with tuberculosis (TB) after the oral administration of RMP in fixed-drug combination formulation. A validated high-performance liquid chromatographic method was used. Pharmacokinetic parameters were estimated with a noncompartmental model. Generalized linear models were obtained by forward steps, and bootstrapping was performed to develop LSS to predict AUC curve from time 0 to the last measured at 24 hours postdose (AUC0-24). The predictive performance of the proposed models was assessed using RMP profiles from 25 other TB patients by comparing predicted and observed AUC0-24.

RESULTS

The mean AUC0-24 in the current study was 91.46 ± 36.7 mg·h·L, and the most convenient sampling time points to predict it were 2, 4 and 12 hours postdose (slope [m] = 0.955 ± 0.06; r = 0.92). The mean prediction error was -0.355%, and the root mean square error was 5.6% in the validation group. Alternate LSSs are proposed with 2 of these sampling time points, which also provide good predictions when the 3 most convenient are not feasible.

CONCLUSIONS

The AUC0-24 for RMP in TB patients can be predicted with acceptable precision through a 2- or 3-point sampling strategy, despite wide interindividual variability. These LSSs could be applied in clinical practice to optimize anti-TB therapy based on therapeutic drug monitoring.

Limited sampling strategy and target attainment analysis for levofloxacin in patients with tuberculosis

There is an urgent need to improve and shorten the treatment of tuberculosis (TB) and multidrug resistant tuberculosis (MDR-TB). Levofloxacin, a newer fluoroquinolone, has potent activity against TB both in vitro and in vivo. Levofloxacin dosing can be optimized to improve the treatment of both TB and MDR-TB. Levofloxacin efficacy is linked primarily to the ratio of the area under the concentration-time curve for the free fraction of drug (fAUC) to the MIC. Since obtaining a full-time concentration profile is not feasible in the clinic, we developed a limited sampling strategy (LSS) to estimate the AUC. We also utilized Monte Carlo simulations to evaluate the dosing of levofloxacin. Pharmacokinetic data were obtained from 10 Brazilian TB patients. The pharmacokinetic data were fitted with a one-compartment model. LSSs were developed using two methods: linear regression and Bayesian approaches. Several LSSs predicted levofloxacin AUC with good accuracy and precision. The most accurate were the method using two samples collected at 4 and 6 h (R(2) = 0.91 using linear regression and 0.97 using Bayesian approaches) and that using samples collected at 2 and 6 h (R(2) = 0.90 using linear regression and 0.96 using Bayesian approaches). The 2-and-6-h approach also provides a good estimate of the maximum concentration of the drug in serum (Cmax). Our target attainment analysis showed that higher doses (17 to 20 mg/kg of body weight) of levofloxacin might be needed to improve its activity. Doses in the range of 17 to 20 mg/kg showed good target attainment for MICs from 0.25 to 0.50. At an MIC of 2, poor target attainment was observed across all doses. This LSS for levofloxacin can be used for therapeutic drug monitoring and for future pharmacokinetic/pharmacodynamic studies.

Review of evidence for measuring drug concentrations of first-line antitubercular agents in adults

Measurement of drug concentrations and performing therapeutic drug monitoring (TDM) are widely used to optimize efficacy and safety of many commonly used drugs today. Although TDM of first-line antitubercular drugs is used during the treatment of tuberculosis, the extent of any benefit achieved is currently unknown. This review summarizes the available literature describing TDM of first-line treatment agents in patients with tuberculosis and describes clinical associations with achievement of target drug concentrations, including data from special populations. A literature review was conducted for articles describing drug concentration and TDM outcomes for first-line tuberculosis agents in adults. A total of 40 studies were included in the review. Studies were a mixture of controlled trials, observational studies, cross-sectional studies, and case reports. The majority of the studies showed standard dosing does not consistently achieve target concentrations for the first-line antitubercular drugs; however, the clinical implications of this finding are still unclear. Presence of HIV and diabetes mellitus appeared to indicate achievement of lower than target concentrations and this warrants further study in prospective studies. Current published data neither prove nor disprove the utility of TDM for general tuberculosis populations but evidence does not currently support routine measurement of drug concentrations.

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

OBJECTIVES

To study 2 h plasma concentrations of the first-line tuberculosis drugs isoniazid, rifampicin, ethambutol and pyrazinamide in a cohort of patients with tuberculosis in Denmark and to determine the relationship between the concentrations and the clinical outcome.

METHODS

After 6-207 days of treatment (median 34 days) 2 h blood samples were collected from 32 patients with active tuberculosis and from three patients receiving prophylactic treatment. Plasma concentrations were determined using LC-MS/MS. Normal ranges were obtained from the literature. Clinical charts 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

Plasma concentrations below the normal ranges were frequently observed: isoniazid in 71%, rifampicin in 58%, ethambutol in 46%, pyrazinamide in 10% and both isoniazid and rifampicin in 45% of the patients. The plasma concentrations of isoniazid correlated inversely with the C-reactive protein level at the time of sampling (P = 0.001). During 1 year of follow-up, therapy failure occurred in five patients. Therapy failure occurred more frequently when the concentrations of isoniazid and rifampicin were both below the normal ranges (P = 0.013) and even more frequently when they were below the median 2 h drug concentrations obtained in the study (P = 0.005).

CONCLUSIONS

At 2 h, plasma concentrations of isoniazid and rifampicin below the normal ranges were frequently observed. The inverse correlation between the plasma concentrations of isoniazid and C-reactive protein indicate a suboptimal treatment effect at standard dosing regimens. Dichotomization based on median 2 h drug concentrations was more predictive of outcome than dichotomization based on normal ranges.

Pharmacokinetics of rifampicin in Mexican patients with tuberculosis and healthy volunteers

OBJECTIVE

The aim of this study was to compare the pharmacokinetics (PK) of rifampicin (RIF) between healthy volunteers and patients with tuberculosis (TB).

METHODS

RIF was administered as a single 600-mg dose to 24 healthy volunteers and 24 TB patients, followed by serial blood sampling. Plasma concentrations were analysed using a chromatographic method, and the PK parameters were estimated using WinNonlin software.

KEY FINDINGS

Peak plasma concentration ranged from 6.4 to 19.9 mg/l, which was subtherapeutic for 15% of the study participants in both groups, mostly in men (71.4%). The mean area under the concentration-time curve (AUC0-24h ) did not show differences between these groups (P > 0.05). The absorption rate was slower in TB patients and the volume of distribution normalized by total body weight (Vd/kg) was greater than healthy volunteers (P < 0.05). A greater Vd and clearance were found in male subjects. The lag time (tlag) and the time before reach Cmax (Tmax) were longer for female TB patients (P < 0.05).

CONCLUSION

The main differences in PK parameters of RIF between Mexican TB patients and healthy volunteers were demonstrated in absorption and distribution processes. In addition, differences in PK parameters observed by sex should be considered for further dosing recommendations.

Sensititre MYCOTB MIC plate for testing Mycobacterium tuberculosis susceptibility to first- and second-line drugs

For Mycobacterium tuberculosis, phenotypic methods for drug susceptibility testing of second-line drugs are poorly standardized and technically challenging. The Sensititre MYCOTB MIC plate (MYCOTB) is a microtiter plate containing lyophilized antibiotics and configured for determination of MICs to first- and second-line antituberculosis drugs. To evaluate the performance of MYCOTB for M. tuberculosis drug susceptibility testing using the Middlebrook 7H10 agar proportion method (APM) as the comparator, we conducted a two-site study using archived M. tuberculosis isolates from Uganda and the Republic of Korea. Thawed isolates were subcultured, and dilutions were inoculated into MYCOTB wells and onto 7H10 agar. MYCOTB results were read at days 7, 10, 14, and 21; APM results were read at 21 days. A total of 222 isolates provided results on both platforms. By APM, 106/222 (47.7%) of isolates were resistant to at least isoniazid and rifampin. Agreement between MYCOTB and APM with respect to susceptibility or resistance was ≥92% for 7 of 12 drugs when a strict definition was used and ≥96% for 10 of 12 drugs when agreement was defined by allowing a ± one-well range of dilutions around the APM critical concentration. For ethambutol, agreement was 80% to 81%. For moxifloxacin, agreement was 83% to 85%; incorporating existing DNA sequencing information for discrepant analysis raised agreement to 91% to 96%. For MYCOTB, the median time to plate interpretation was 10 days and interreader agreement was ≥95% for all drugs. MYCOTB provided reliable results for M. tuberculosis susceptibility testing of first- and second-line drugs except ethambutol, and results were available sooner than those determined by APM.

Plasma concentrations of isoniazid and rifampin are decreased in adult pulmonary tuberculosis patients with diabetes mellitus

Plasma isoniazid and rifampin concentrations, but not pyrazinamide and ethambutol concentrations, were decreased by about 50% (P < 0.05) in diabetic pulmonary tuberculosis patients. The prevalences of subnormal plasma isoniazid, rifampin, pyrazinamide, and ethambutol concentrations were 49% or 100% (P < 0.01), 66% or 100% (P < 0.05), 30% or 50% (P = 0.198), and 32% or 21% (P = 0.742) in nondiabetic or diabetic tuberculosis patients, respectively. These data show that plasma concentrations of isoniazid and rifampin were greatly reduced in diabetic tuberculosis patients.

Isoniazid, rifampin, and pyrazinamide plasma concentrations in relation to treatment response in Indonesian pulmonary tuberculosis patients

Numerous studies have reported low concentrations of antituberculosis drugs in tuberculosis (TB) patients, but few studies have examined whether low drug concentrations affect TB treatment response. We examined steady-state plasma concentrations of isoniazid, rifampin, and pyrazinamide at 2 h after the administration of drugs (C(2 h)) among 181 patients with pulmonary tuberculosis in Indonesia and related these to bacteriological response during treatment. C(2 h) values below reference values for either isoniazid, rifampin, or pyrazinamide were found in 91% of patients; 60% had at least two low C(2 h) concentrations. The isoniazid C2 h was noticeably lower in fast versus slow acetylators (0.9 mg/liter versus 2.2 mg/liter, P < 0.001). At the end of treatment, 82% of the patients were cured, whereas 30 patients (17%) had dropped out during the study, and 2 patients (1%) failed treatment. No association was found between C(2 h) concentrations and sputum culture results at 8 weeks of treatment. Post hoc analysis showed that patients with low pyrazinamide C2 h (P = 0.01) and patients with large extensive lung lesions (P = 0.01) were at risk of at least one positive culture at week 4, 8, or 24/32. Antituberculosis drug concentrations were often low, but treatment response was nevertheless good. No association was found between drug concentrations and 8 weeks culture conversion, but low pyrazinamide drug concentrations may be associated with a less favorable bacteriological response. The use of higher doses of pyrazinamide may warrant further investigation.

Method for simultaneous analysis of nine second-line anti-tuberculosis drugs using UPLC-MS/MS

OBJECTIVES

Therapeutic drug monitoring (TDM) of anti-tuberculosis (TB) drugs is beneficial for patients responding slowly to treatment and those with multidrug-resistant TB. We used ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) to develop a rapid method for simultaneously measuring the blood concentrations of nine second-line anti-TB drugs: streptomycin, kanamycin, clarithromycin, cycloserine, moxifloxacin, levofloxacin, para-aminosalicylic acid, prothionamide and linezolid.

METHODS

Serum samples were extracted with acidified methanol and neutralized with NaOH. A Waters Acquity HSS T3 column and gradients of ammonium formate and acetonitrile in 0.1% formic acid were used for UPLC separation. Drug concentrations were determined by multiple reaction monitoring in positive ion mode, and assay performance was evaluated. We applied this method to TDM, analysing random serum samples from 85 patients treated with second-line drugs.

RESULTS

Sample preparation using acidified methanol extraction followed by neutralization yielded good recovery and ionization efficiency, with chromatographic separation achieved within 3 min per sample. Within-run and between-run precisions were 1.7%-7.5% and 1.7%-12.4%, respectively, at concentrations representing low and high levels for the nine drugs. Lower limits of detection and quantification were 0.025-0.5 and 0.25-5.0 μg/mL, respectively. Linearity was acceptable at five concentrations for each drug. No ion suppression was observed at the retention time for most compounds, except for streptomycin, kanamycin and cycloserine, which were eluted close to the void volume of the column. In a limited pilot study, all quantifiable human samples had values within the validated assay ranges.

CONCLUSIONS

The performance of our MS/MS detection technique was generally acceptable. The method provided rapid, sensitive and reproducible quantification of nine second-line anti-TB drugs and should facilitate drug monitoring during treatment.

Hepatotoxicity Related to Anti-tuberculosis Drugs: Mechanisms and Management

Development of idiosyncratic hepatotoxicity is an intricate process involving both concurrent as well as sequential events determining the direction of the pathways, degree of liver injury and its outcome. Decades of clinical observation have identified a number of drug and host related factors that are associated with an increased risk of antituberculous drug-induced hepatotoxicity, although majority of the studies are retrospective with varied case definitions and sample sizes. Investigations on genetic susceptibility to hepatotoxicity have so far focused on formation and accumulation reactive metabolite as well as factors that contribute to cellular antioxidant defense mechanisms and the environment which can modulate the threshold for hepatocyte death secondary to oxidative stress. Recent advances in pharmacogenetics have promised the development of refined algorithms including drug, host and environmental risk factors that allow better tailoring of medications based on accurate estimates of risk-benefit ratio. Future investigations exploring the pathogenesis of hepatotoxicity should be performed using human tissue and samples whenever possible, so that the novel findings can be translated readily into clinical applications.