Limited sampling strategies for therapeutic drug monitoring of amikacin and kanamycin in patients with multidrug-resistant tuberculosis

Limited sampling strategies for therapeutic drug monitoring of anti-tuberculosis medications: A systematic review of their feasibility and clinical utility

Therapeutic drug monitoring (TDM) is recommended for medications with high inter-individual variability, narrow therapeutic index drugs, possible drug-drug interactions, drug toxicity, and subtherapeutic concentrations, as well as to assess noncompliance. The area under the plasma concentration-time curve (AUC) is a significant pharmacokinetic parameter since it calculates the drug's total systematic exposure in the body. However, multiple blood samples from the patient are required to calculate the area under the curve, which is inconvenient for both the patient and the healthcare professional. To alleviate the issue, the limited sampling strategy (LSS) was devised, in which sampling is minimized while obtaining complete and precise findings to anticipate the area under the curve. One can reduce costs, labor, and discomfort for patients and healthcare workers by applying this limited sampling strategy. This article examines a systematic evaluation of all the limited sampling done in anti-tuberculosis (anti-TB) medications resulting from the literature search of several research papers. This article also briefly describes the two methodologies: Multiple regression analysis (MRA) and the Bayesian approach used to develop a limited sampling strategy model. Anti-TB medications have been found to have considerable inter-individual variability, and isoniazid has a narrow therapeutic index, both of which are criteria for therapeutic drug monitoring. To avoid multi-drug resistance and therapy failure, it is proposed that limited sampling strategy-based therapeutic drug monitoring of anti-TB medications be undertaken to generate an individualized dose regimen, particularly for individuals at high risk of treatment failure or delayed response.

Tuberkulose im Erwachsenenalter

Die Tuberkulose ist in Deutschland eine seltene, überwiegend gut behandelbare Erkrankung. Weltweit ist sie eine der häufigsten Infektionserkrankungen mit ca. 10 Millionen Neuerkrankungen/Jahr. Auch bei einer niedrigen Inzidenz in Deutschland bleibt Tuberkulose insbesondere aufgrund der internationalen Entwicklungen und Migrationsbewegungen eine wichtige Differenzialdiagnose. In Deutschland besteht, aufgrund der niedrigen Prävalenz der Erkrankung und der damit verbundenen abnehmenden klinischen Erfahrung, ein Informationsbedarf zu allen Aspekten der Tuberkulose und ihrer Kontrolle. Diese Leitlinie umfasst die mikrobiologische Diagnostik, die Grundprinzipien der Standardtherapie, die Behandlung verschiedener Organmanifestationen, den Umgang mit typischen unerwünschten Arzneimittelwirkungen, die Besonderheiten in der Diagnostik und Therapie resistenter Tuberkulose sowie die Behandlung bei TB-HIV-Koinfektion. Sie geht darüber hinaus auf Versorgungsaspekte und gesetzliche Regelungen wie auch auf die Diagnosestellung und präventive Therapie einer latenten tuberkulösen Infektion ein. Es wird ausgeführt, wann es der Behandlung durch spezialisierte Zentren bedarf.

Die Aktualisierung der S2k-Leitlinie „Tuberkulose im Erwachsenenalter“ soll allen in der Tuberkuloseversorgung Tätigen als Richtschnur für die Prävention, die Diagnose und die Therapie der Tuberkulose dienen und helfen, den heutigen Herausforderungen im Umgang mit Tuberkulose in Deutschland gewachsen zu sein.

Therapeutic Drug Monitoring in Non-Tuberculosis Mycobacteria Infections

Nontuberculous mycobacteria can cause minimally symptomatic self-limiting infections to progressive and life-threatening disease of multiple organs. Several factors such as increased testing and prevalence have made this an emerging infectious disease. Multiple guidelines have been published to guide therapy, which remains difficult owing to the complexity of therapy, the potential for acquired resistance, the toxicity of treatment, and a high treatment failure rate. Given the long duration of therapy, complex multi-drug treatment regimens, and the risk of drug toxicity, therapeutic drug monitoring is an excellent method to optimize treatment. However, currently, there is little available guidance on therapeutic drug monitoring for this condition. The aim of this review is to provide information on the pharmacokinetic/pharmacodynamic targets for individual drugs used in the treatment of nontuberculous mycobacteria disease. Lacking data from randomized controlled trials, in vitro, in vivo, and clinical data were aggregated to facilitate recommendations for therapeutic drug monitoring to improve efficacy and reduce toxicity.

Population Pharmacokinetics and Bayesian Dose Adjustment to Advance TDM of Anti-TB Drugs

Tuberculosis (TB) is still the number one cause of death due to an infectious disease. Pharmacokinetics and pharmacodynamics of anti-TB drugs are key in the optimization of TB treatment and help to prevent slow response to treatment, acquired drug resistance, and adverse drug effects. The aim of this review was to provide an update on the pharmacokinetics and pharmacodynamics of anti-TB drugs and to show how population pharmacokinetics and Bayesian dose adjustment can be used to optimize treatment. We cover aspects on preclinical, clinical, and population pharmacokinetics of different drugs used for drug-susceptible TB and multidrug-resistant TB. Moreover, we include available data to support therapeutic drug monitoring of these drugs and known pharmacokinetic and pharmacodynamic targets that can be used for optimization of therapy. We have identified a wide range of population pharmacokinetic models for first- and second-line drugs used for TB, which included models built on NONMEM, Pmetrics, ADAPT, MWPharm, Monolix, Phoenix, and NPEM2 software. The first population models were built for isoniazid and rifampicin; however, in recent years, more data have emerged for both new anti-TB drugs, but also for defining targets of older anti-TB drugs. Since the introduction of therapeutic drug monitoring for TB over 3 decades ago, further development of therapeutic drug monitoring in TB next steps will again depend on academic and clinical initiatives. We recommend close collaboration between researchers and the World Health Organization to provide important guideline updates regarding therapeutic drug monitoring and pharmacokinetics/pharmacodynamics.

Population Pharmacokinetic Models of Antituberculosis Drugs in Patients: A Systematic Critical Review

BACKGROUND

Tuberculosis (TB) remains one of the most important infectious diseases. Population pharmacokinetic (pop-PK) models are widely used to individualize dosing regimens of several antibiotics, but their application in anti-TB drug studies is scant. The aim of this study was to provide an insight regarding the status of pop-PK for these drugs and to compare results obtained through both parametric and nonparametric approaches to design precise dosage regimens.

METHODS

First, a systematic approach was implemented, searching in PubMed and Google Scholar. Articles that did not include human patients, that lacked an explicit structural model, that analyzed drugs inactive against M. tuberculosis, or were without full-text access, were excluded. Second, the PK parameters were summarized and categorized as parametric versus nonparametric results. Third, a Monte Carlo simulation was performed in Pmetrics using the results of both groups, and an error term was built to describe the imprecision of each PK modeling approach.

RESULTS

Thirty-three articles reporting at least 1 pop-PK model of 19 anti-TB drug were found; 46 different models including PK parameter estimates and their relevant covariates were also reported. Only 9 models were based on nonparametric approaches. Rifampin was the drug most studied, but only using parametric approaches. The simulations showed that nonparametric approaches improve the error term compared with parametric approaches.

CONCLUSIONS

More and better models, ideally using nonparametric approaches linked with clear pharmacodynamic goals, are required to optimize anti-TB drug dosing, as recommended in the WHO End TB strategy.

Therapeutic drug monitoring in patients with tuberculosis and concurrent medical problems

INTRODUCTION

Therapeutic drug monitoring (TDM) has been recommended for treatment optimization in tuberculosis (TB) but is only is used in certain countries e.g. USA, Germany, the Netherlands, Sweden and Tanzania. Recently, new drugs have emerged and PK studies in TB are continuing, which contributes further evidence for TDM in TB. The aim of this review is to provide an update on drugs used in TB, treatment strategies for these drugs, and TDM to support broader implementation.

AREAS COVERED

This review describes the different drug classes used for TB, multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB), along with their pharmacokinetics, dosing strategies, TDM and sampling strategies. Moreover, the review discusses TDM for patient TB and renal or liver impairment, patients co-infected with HIV or hepatitis, and special patient populations - children and pregnant women.

EXPERT OPINION

TB treatment has a long history of using 'one size fits all.' This has contributed to treatment failures, treatment relapses, and the selection of drug-resistant isolates. While challenging in resource-limited circumstances, TDM offers the clinician the opportunity to individualize and optimize treatment early in treatment. This approach may help to refine treatment and thereby reduce adverse effects and poor treatment outcomes. Funding, training, and randomized controlled trials are needed to advance the use of TDM for patients with TB.

Population pharmacokinetic evaluation and optimization of amikacin dosage regimens for the management of mycobacterial infections

Background

There is limited information on amikacin pharmacokinetics (PK) and dose requirements in patients with mycobacterial infections.

Objectives

To conduct a population PK analysis of amikacin data from patients with mycobacterial infections and compare predicted concentrations from standard and modified dosage guidelines with recommended target ranges.

Methods

A population PK model was developed using NONMEM. Cmax, Cmin, concentration 1 h post-infusion (C1h) and AUC0–24 using 15 mg/kg daily (once daily), the WHO table, 25 mg/kg three times weekly (TTW) and modified guidelines were compared using Monte Carlo simulations of 1000 patients.

Results

Data were available from 124 patients (684 concentrations) aged 16–92 years. CL was 4.64 L/h per 100 mL/min CLCR; V was 0.344 L/kg. With once-daily regimens, Cmax was 35–45 mg/L in 30%–35% of patients and 35–50 mg/L in 46%–48%; C1h was 25–40 mg/L in 53%–59%. The WHO table produced high Cmax values in patients <60 kg and low in patients >75 kg. With TTW dosing, around 30% of Cmax values were 65–80 mg/L, 40% were 60–80 mg/L, and 48% of C1h were 45–65 mg/L. Increasing the dosage interval for patients with CLCR <50 mL/min reduced Cmin values >2 mg/L from 34% to 25% for once-daily dosing and from 18% to 13% for TTW. In patients whose Cmin was <2 mg/L, 82% of AUC0–24 values were 100–300 mg.h/L.

Conclusions

Standard amikacin dosing guidelines achieve low percentages of target concentrations for mycobacterial infections. Extending the dosing interval in renal impairment and widening target ranges would reduce the need for dose adjustment.

Pharmacokinetic Modeling, Simulation, and Development of a Limited Sampling Strategy of Cycloserine in Patients with Multidrug-/Extensively Drug-Resistant Tuberculosis

BACKGROUND AND OBJECTIVE

Multidrug-resistant tuberculosis has much poorer treatment outcomes compared with drug-susceptible tuberculosis because second-line drugs for treating multidrug resistant tuberculosis are less effective and are frequently associated with side effects. Optimization of drug treatment is urgently needed. Cycloserine is a second-line tuberculosis drug with variable pharmacokinetics and thus variable exposure when programmatic doses are used. The objective of this study was to develop a population pharmacokinetic model of cycloserine to assess drug exposure and to develop a limited sampling strategy for cycloserine exposure monitoring.

MATERIAL AND METHODS

Patients with multidrug-/extensively drug-resistant tuberculosis who were treated for > 7 days with cycloserine were eligible for inclusion. Patients received cycloserine 500 mg (body weight ≤ 50 kg) or 750 mg (body weight > 50 kg) once daily. MW/Pharm 3.83 (Mediware, Groningen, The Netherlands) was used to parameterize the population pharmacokinetic model. The model was compared with pharmacokinetic values from the literature and evaluated with a bootstrap analysis, Monte Carlo simulation, and an external dataset. Monte Carlo simulations were used to develop a limited sampling strategy.

RESULTS

Cycloserine plasma concentration vs time curves were obtained from 15 hospitalized patients (nine male, six female, median age 35 years). Mean dose/kg body weight was 11.5 mg/kg (standard deviation 2.04 mg/kg). Median area under the concentration-time curve over 24 h (AUC_0-24 h) of cycloserine was 888 h mg/L (interquartile range 728-1252 h mg/L) and median maximum concentration of cycloserine was 23.31 mg/L (interquartile range 20.14-33.30 mg/L). The final population pharmacokinetic model consisted of the following pharmacokinetic parameters [mean (standard deviation)]: absorption constant K_{a_po} of 0.39 (0.31) h^-1, distribution over the central compartment (V_d) of 0.54 (0.26) L/kg LBM, renal clearance as fraction of the estimated glomerular filtration rate of 0.092 (0.038), and metabolic clearance of 1.05 (0.75) L/h. The population pharmacokinetic model was successfully evaluated with a bootstrap analysis, Monte Carlo simulation, and an external dataset of Chinese patients (difference of 14.6% and 19.5% in measured and calculated concentrations and AUC_0-24 h, respectively). Root-mean-squared-errors found in predicting the AUC_0-24 h using a one- (4 h) and a two- (2 h and 7 h) limited sampling strategy were 1.60% and 0.14%, respectively.

CONCLUSIONS

This developed population pharmacokinetic model can be used to calculate cycloserine concentrations and exposure in patients with multidrug-/extensively drug-resistant tuberculosis. This model was successfully validated by internal and external validation methods. This study showed that the AUC_0-24 h of cycloserine can be estimated in patients with multidrug-/extensively drug-resistant tuberculosis using a 1- or 2-point limited sampling strategy in combination with the developed population pharmacokinetic model. This strategy can be used in studies to correlate drug exposure with clinical outcome. This study also showed that good target attainment rates, expressed by time above the minimal inhibitory concentration, were obtained for cycloserine with a minimal inhibitory concentration of 5 and 10 mg/L, but low rates with a minimal inhibitory concentration of 20 and 32.5 mg/L.

Amikacin Dosing for MDR Tuberculosis: A Systematic Review to Establish or Revise the Current Recommended Dose for Tuberculosis Treatment

Background

Amikacin has been used for over 40 years in multidrug resistant tuberculosis (MDR-TB), but there is still debate on the right dose. The aim of this review was to search relevant pharmacokinetic (PK) and pharmacodynamic (PD) literature for the optimal dose and dosing frequency of amikacin in MDR-TB regimens trying to optimize efficacy while minimizing toxicity.

Methods

A systematic review on the value of amikacin as second-line drug in the treatment of MDR-TB was performed.

Results

Five articles were identified with data on PK, hollow-fiber system model for TB and or early bactericidal activity of amikacin. Despite the long period in which amikacin has been available for the treatment of MDR-TB, very little PK data is available. This highlights the need for more research.

Conclusions

Maximum concentration (Cmax) of amikacin related to MIC proved to be the most important PK/PD index for efficacy. The target Cmax/MIC ratio should be 10 at site of infection. Cumulative area under the concentration-time curve (AUC) corresponding with cumulative days of treatment was associated with an increased risk of toxicity.

Limited Sampling Strategies Using Linear Regression and the Bayesian Approach for Therapeutic Drug Monitoring of Moxifloxacin in Tuberculosis Patients

Therapeutic drug monitoring (TDM) of moxifloxacin is recommended to improve the response to tuberculosis treatment and reduce acquired drug resistance. Limited sampling strategies (LSSs) are able to reduce the burden of TDM by using a small number of appropriately timed samples to estimate the parameter of interest, the area under the concentration-time curve. This study aimed to develop LSSs for moxifloxacin alone (MFX) and together with rifampin (MFX+RIF) in tuberculosis (TB) patients. Population pharmacokinetic (popPK) models were developed for MFX (n = 77) and MFX+RIF (n = 24). In addition, LSSs using Bayesian approach and multiple linear regression were developed. Jackknife analysis was used for internal validation of the popPK models and multiple linear regression LSSs. Clinically feasible LSSs (one to three samples, 6-h timespan postdose, and 1-h interval) were tested. Moxifloxacin exposure was slightly underestimated in the one-compartment models of MFX (mean -5.1%, standard error [SE] 0.8%) and MFX+RIF (mean -10%, SE 2.5%). The Bayesian LSSs for MFX and MFX+RIF (both 0 and 6 h) slightly underestimated drug exposure (MFX mean -4.8%, SE 1.3%; MFX+RIF mean -5.5%, SE 3.1%). The multiple linear regression LSS for MFX (0 and 4 h) and MFX+RIF (1 and 6 h), showed mean overestimations of 0.2% (SE 1.3%) and 0.9% (SE 2.1%), respectively. LSSs were successfully developed using the Bayesian approach (MFX and MFX+RIF; 0 and 6 h) and multiple linear regression (MFX, 0 and 4 h; MFX+RIF, 1 and 6 h). These LSSs can be implemented in clinical practice to facilitate TDM of moxifloxacin in TB patients.

Ready for TDM: Simultaneous quantification of amikacin, vancomycin and creatinine in human plasma employing ultra-performance liquid chromatography-tandem mass spectrometry

BACKGROUND

Amikacin (AMI) and vancomycin (VAN) are antibiotics largely used in intensive care in the empiric treatment of severe infections by multi-resistant gram-negative and gram-positive bacteria. AMI and VAN are eliminated untransformed by glomerular filtration, showing depuration ratio highly correlated with creatinine (CRE) clearance. AMI, VAN and CRE are highly polar structures, presenting poor retention in reversed-phase liquid chromatography when using conventional stationary phases.

OBJECTIVE

This study aimed to develop and validate a simple UPLC-MS/MS method for simultaneous determination of AMI, VAN, and CRE in human plasma for therapeutic drug monitoring.

RESULTS

Samples were prepared by protein precipitation, followed by dilution. Heptafluorobutyric acid (HFBA) was added to the mobile phase at low concentration (0.01%), and separation was performed in an ultra-performance reversed-phase column (particle diameter of 1.8 μm). These conditions allowed retention times of 0.92, 0.93, 2.12, 2.17 and 2.27 min for CRE, CRE-D3, AMI, KAN and VAN, respectively. The assay was linear from 0.5 to 100 mg L^-1 for AMI and VAN and 5 to 100 mg L^-1. Precision, accuracy and stability assays were acceptable according to bioanalytical validation guidelines. Suitable results. Matrix effects were in the range of +10.5 to +11.6% for AMI, -4.3 to -4.5% for VAN, and - 1.7 to +0.7 for CRE.

CONCLUSION

The first assay for the simultaneous determination of AMI, VAN and CRE in plasma by liquid chromatography-tandem mass spectrometry was reported. This assay allows the obtention of the necessary analytical data for the clinical application of population pharmacokinetic methods for therapeutic drug monitoring of AMI and VAN.

Population Pharmacokinetics of Amikacin in Adult Patients with Cystic Fibrosis

Practitioners commonly use amikacin in patients with cystic fibrosis. Establishment of the pharmacokinetics of amikacin in adults with cystic fibrosis may increase the efficacy and safety of therapy. This study was aimed to establish the population pharmacokinetics of amikacin in adults with cystic fibrosis. We used serum concentration data obtained during routine therapeutic drug monitoring and explored the influence of patient covariates on drug disposition. We performed a retrospective chart review to collect the amikacin dosing regimens, serum amikacin concentrations, blood sampling times, and patient characteristics for adults with cystic fibrosis admitted for treatment of acute pulmonary exacerbations. Amikacin concentrations were retrospectively collected for 49 adults with cystic fibrosis, and 192 serum concentrations were available for analysis. A population pharmacokinetic model was developed using nonlinear mixed-effects modeling with the first-order conditional estimation method. A two-compartment model with first-order elimination best described amikacin pharmacokinetics. Creatinine clearance and weight were identified as significant covariates for clearance and the volume of distribution, respectively, in the final model. Residual variability was modeled using a proportional error model. Typical estimates for clearance, central and peripheral volumes of distribution, and intercompartmental clearance were 3.06 liters/h, 14.4 liters, 17.1 liters, and 0.925 liters/h, respectively. The pharmacokinetics of amikacin in individuals with cystic fibrosis seems to differ from those in individuals without cystic fibrosis. However, further investigations are needed to confirm these results and, thus, the need for variations in amikacin dosing. Future pharmacodynamic studies will potentially establish the optimal amikacin dosing regimens for the treatment of acute pulmonary exacerbations in adult patients with CF.

Perspectives for personalized therapy for patients with multidrug-resistant tuberculosis

According to the World Health Organization (WHO), tuberculosis is the leading cause of death attributed to a single microbial pathogen worldwide. In addition to the large number of patients affected by tuberculosis, the emergence of Mycobacterium tuberculosis drug-resistance is complicating tuberculosis control in many high-burden countries. During the past 5 years, the global number of patients identified with multidrug-resistant tuberculosis (MDR-TB), defined as bacillary resistance at least against rifampicin and isoniazid, the two most active drugs in a treatment regimen, has increased by more than 20% annually. Today we experience a historical peak in the number of patients affected by MDR-TB. The management of MDR-TB is characterized by delayed diagnosis, uncertainty of the extent of bacillary drug-resistance, imprecise standardized drug regimens and dosages, very long duration of therapy and high frequency of adverse events which all translate into a poor prognosis for many of the affected patients. Major scientific and technological advances in recent years provide new perspectives through treatment regimens tailor-made to individual needs. Where available, such personalized treatment has major implications on the treatment outcomes of patients with MDR-TB. The challenge now is to bring these adances to those patients that need them most.

Modalities to monitor the treatment response in tuberculosis

Considering the global epidemic of drug resistance in Mycobacterium tuberculosis, early and accurate diagnosis as well as prompt initiation of antitubercular therapy (ATT) forms the mainstay of tuberculosis control programs. Patients on ATT may develop treatment failure due to diverse reasons including emergence of drug resistance in the host during the course of therapy. Monitoring the timely response to treatment in such cases has a significant role in rapid identification of drug resistant strains and institution of change of regimen to further decrease the morbidity and mortality associated with the disease. Furthermore, availability of faster surrogate end points to assess treatment efficacy, disease activity, cure, and relapse is one of the crucial requirements for undertaking innovative clinical trials related to TB. The article presents here the compilation of currently available methods for monitoring the treatment response in pulmonary as well as extrapulmonary TB.

In Vitro Susceptibility of Mycobacterium tuberculosis to Amikacin, Kanamycin, and Capreomycin

Amikacin, kanamycin, and capreomycin are among the most important second-line drugs for multidrug-resistant tuberculosis. Although amikacin and kanamycin are administered at the same dose and show the same pharmacokinetics, they have different WHO breakpoints, suggesting that the two drugs have different MICs. The aim of this study was to investigate possible differences in MICs between the aminoglycosides and capreomycin. Using the direct concentration method, a range of concentrations of amikacin, kanamycin, and capreomycin (0.25, 0.50, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0, and 64.0 mg/liter) were tested against 57 clinical Mycobacterium tuberculosis strains. The 7H10 agar plates were examined for mycobacterial growth after 14 days. At 2 mg/liter, 48 strains (84%) were inhibited by amikacin and only 5 strains (9%) were inhibited by kanamycin (P < 0.05, Wilcoxon signed-rank test). The median MICs of amikacin, kanamycin, and capreomycin were 2, 4, and 8 mg/liter, respectively. No difference in amikacin, kanamycin, and capreomycin MIC distributions was observed between multidrug-resistant strains and fully susceptible strains. The results indicate that amikacin is more active than kanamycin and capreomycin against M. tuberculosis with the absolute concentration method. Determination of the impact of this difference on clinical outcomes in daily practice requires a prospective study, including pharmacokinetic and pharmacodynamic evaluations.

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 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.

Population pharmacokinetics of moxifloxacin, cycloserine, p-aminosalicylic acid and kanamycin for the treatment of multi-drug-resistant tuberculosis

Control of multi-drug-resistant tuberculosis (MDR-TB) requires extensive, supervised chemotherapy because second-line anti-TB drugs have a narrower therapeutic range than first-line drugs. This study aimed to develop population pharmacokinetic (PK) models for second-line drugs in patients with MDR-TB, evaluate the recommended dosage regimens and, if necessary, suggest new dosage regimens. A prospective, single-centre PK study was performed on second-line anti-TB drugs in patients with MDR-TB. Moxifloxacin, cycloserine, p-aminosalicylic acid (PAS), kanamycin and other second-line drugs were administered to the patients. Plasma concentrations were analysed using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Population PK models were developed using non-linear mixed effect modelling (NONMEM, Version 7.30; ICON Development Solutions, Ellicott City, MD, USA). Simulations were performed using the calculated PK parameters. The respective absorption rate constant, apparent clearance and apparent volume of distribution values were as follows: 0.305/h, 9.37 L/h and 56.7 L for moxifloxacin; 0.135/h, 1.38 L/h and 10.5 L for cycloserine; 0.510/h, 30.8 L/h and 79.4 L for PAS; and 1.67/h, 3.75 L/h and 15.2 L for kanamycin. The simulations showed that the following dosage regimens were more likely to be within the recommended concentration ranges than the raw data in this study: 200 mg of moxifloxacin once daily (QD) (patient weight <50 kg) and 400 mg of moxifloxacin QD (patient weight ≥50 kg), 500-750 mg of cycloserine QD, 4.95-6.6 g of PAS twice daily and 750-1000 mg of intramuscular kanamycin QD. These findings indicate that the recommended doses should be revised to improve the clinical outcomes of MDR-TB treatment.

Kanamycin Sulphate Loaded PLGA-Vitamin-E-TPGS Long Circulating Nanoparticles Using Combined Coating of PEG and Water-Soluble Chitosan

Kanamycin sulphate (KS) is a Mycobacterium tuberculosis protein synthesis inhibitor. Due to its intense hydrophilicity, KS is cleared from the body within 8 h. KS has a very short plasma half-life (2.5 h). KS is used in high concentrations to reach the therapeutic levels in plasma, which results in serious nephrotoxicity/ototoxicity. To overcome aforementioned limitations, the current study aimed to develop KS loaded PLGA-Vitamin-E-TPGS nanoparticles (KS-PLGA-TPGS NPs), to act as an efficient carrier for controlled delivery of KS. To achieve a substantial extension in blood circulation, a combined design, affixation of polyethylene glycol (PEG) to KS-PLGA-TPGS NPs and adsorption of water-soluble chitosan (WSC) (cationic deacetylated chitin) to particle surface, was raised for surface modification of NPs. Surface modified NPs (KS-PEG-WSC NPs) were prepared to provide controlled delivery and circulate in the bloodstream for an extended period of time, thus minimizing dosing frequency. In vivo pharmacokinetics and in vivo biodistribution following intramuscular administration were investigated. NPs surface charge was close to neutral +3.61 mV and significantly affected by the WSC coating. KS-PEG-WSC NPs presented striking prolongation in blood circulation, reduced protein binding, and long drew-out the blood circulation half-life with resultant reduced kidney sequestration vis-à-vis KS-PLGA-TPGS NPs. The studies, therefore, indicate the successful formulation development of KS-PEG-WSC NPs with reduced frequency of dosing of KS indicating low incidence of nephrotoxicity/ototoxicity.

Reduced Chance of Hearing Loss Associated with Therapeutic Drug Monitoring of Aminoglycosides in the Treatment of Multidrug-Resistant Tuberculosis

Hearing loss and nephrotoxicity are associated with prolonged treatment duration and higher dosage of amikacin and kanamycin. In our tuberculosis center, we used therapeutic drug monitoring (TDM) targeting preset pharmacokinetic/pharmacodynamic (PK/PD) surrogate endpoints in an attempt to maintain efficacy while preventing (oto)toxicity. To evaluate this strategy, we retrospectively evaluated medical charts of tuberculosis (TB) patients treated with amikacin or kanamycin in the period from 2000 to 2012. Patients with culture-confirmed multiresistant or extensively drug-resistant tuberculosis (MDR/XDR-TB) receiving amikacin or kanamycin as part of their TB treatment for at least 3 days were eligible for inclusion in this retrospective study. Clinical data, including maximum concentration (C_max), C_min, and audiometry data, were extracted from the patients' medical charts. A total of 80 patients met the inclusion criteria. The mean weighted C_max/MIC ratios obtained from 57 patients were 31.2 for amikacin and 12.3 for kanamycin. The extent of hearing loss was limited and correlated with the cumulative drug dose per kg of body weight during daily administration. At follow-up, 35 (67.3%) of all patients had successful outcome; there were no relapses. At a median dose of 6.5 mg/kg, a correlation was found between the dose per kg of body weight during daily dosing and the extent of hearing loss in dB at 8,000 Hz. These findings suggest that the efficacy at this lower dosage is maintained with limited toxicity. A randomized controlled trial should provide final proof of the safety and efficacy of TDM-guided use of aminoglycosides in MDR-TB treatment.

Comparative study of kanamycin sulphate microparticles and nanoparticles for intramuscular administration: preparation in vitro release and preliminary in vivo evaluation

Kanamycin sulphate (KS) is a Mycobacterium tuberculosis protein synthesis inhibitor. KS is polycationic, a property responsible for KS poor oral absorption half-life (2.5 h) and rapid renal clearance, which results in serious nephrotoxicity/ototoxicity. The current study aimed to develop KS-loaded PLGA vitamin-E-TPGS microparticles (MPs) and nanoparticles (NPs) to reduce the dosing frequency and dose-related adverse effect. In vitro release was sustained up to 10 days for KS PLGA-TPGS MPs and 13 days for KS PLGA-TPGS NPs in phosphate-buffered saline (PBS) pH 7.4. The in vivo pharmacokinetic test in Wistar rats showed that the AUC_0-∞ of KS PLGA-TPGS NPs (280.58 μg/mL*min) was about 1.62-fold higher than that of KS PLGA-TPGS MPs (172.30 μg/mL*min). Further, in vivo protein-binding assay ascribed 1.20-fold increase in the uptake of KS PLGA-TPGS NPs through the alveolar macrophage (AM). The studies, therefore, could provide another useful tool for successful development of KS MPs and NPs.

The safety and tolerability of the second-line injectable antituberculosis drugs in children

INTRODUCTION

A growing number of children globally are being treated for multidrug-resistant tuberculosis (MDR-TB). The second-line injectable antituberculosis medications amikacin, kanamycin and capreomycin, traditionally a mainstay of MDR-TB treatment, cause important adverse effects including permanent sensorineural hearing loss, nephrotoxicity, electrolyte abnormalities, injection pain and local injection site complications. Areas covered: To characterize the safety and tolerability of the second-line injectables in children treated for MDR-TB, we reviewed data on the mechanism of injectable associated adverse effects, risk factors for their development, and the incidence of injectable-associated adverse effects in adults and children treated for MDR-TB. Expert opinion: Despite a substantial evidence base in adults demonstrating the frequent and potentially serious adverse effects of second-line injectables, important knowledge gaps remain. Improved characterization of the incidence of injectable-associated adverse effects will inform rational guidance on monitoring children with TB on injectables. Eliminating the need for injectables in MDR-TB treatment regimens is a high priority, and will rely on the use of novel antituberculosis TB drugs. Strategies to reduce the risk of adverse effects of injectables, if used, deserve evaluation. This includes evaluation of potentially otoprotective medications N-acetylcysteine or aspirin, high frequency hearing screening for earlier detection of ototoxicity and therapeutic drug monitoring.

Immunoassay Analysis of Kanamycin in Serum Using the Tobramycin Kit

Kanamycin is one of the aminoglycosides used in the treatment of multidrug-resistant tuberculosis. Blood concentrations of kanamycin are predictive for the treatment efficacy and the occurrence of side effects, and dose adjustments can be needed to optimize therapy. However, an immunoassay method for the quantification of kanamycin is not commercially available. We modified the existing tobramycin immunoassay to analyze kanamycin. This modified method was tested in a concentration range of 0.3 to 80.0 mg/liter for inaccuracy and imprecision. In addition, the analytical results of the immunoassay method were compared to those obtained by a liquid chromatography-tandem mass spectrometry (LC-MS/MS) analytical method using Passing and Bablok regression. Within-day imprecision varied from 2.3 to 13.3%, and between-day imprecision ranged from 0.0 to 11.3%. The inaccuracy ranged from -5.2 to 7.6%. No significant cross-reactivity with other antimicrobials and antiviral agents was observed. The results of the modified immunoassay method were comparable with the LC-MS/MS analytical outcome. This new immunoassay method enables laboratories to perform therapeutic drug monitoring of kanamycin without the need for complex and expensive LC-MS/MS equipment.

Pharmacokinetic Evaluation of Sulfamethoxazole at 800 Milligrams Once Daily in the Treatment of Tuberculosis

For treatment of multidrug-resistant tuberculosis (MDR-TB), there is a scarcity of antituberculosis drugs. Co-trimoxazole is one of the available drug candidates, and it is already frequently coprescribed for TB-HIV-coinfected patients. However, only limited data are available on the pharmacokinetic (PK) and pharmacodynamic (PD) parameters of co-trimoxazole in TB patients. The objective of this study was to evaluate the PK parameters and in vitro PD data on the effective part of co-trimoxazole: sulfamethoxazole. In a prospective PK study in patients infected with drug-susceptible Mycobacterium tuberculosis (drug-susceptible TB patients) (age, >18), sulfamethoxazole-trimethoprim (SXT) was administered orally at a dose of 960 mg once daily. One-compartment population pharmacokinetic modeling was performed using MW\Pharm 3.81 (Mediware, Groningen, The Netherlands). The area under the concentration-time curve for the free, unbound fraction of a drug (ƒAUC)/MIC ratio and the period in which the free concentration exceeded the MIC (fT > MIC) were calculated. Twelve patients received 960 mg co-trimoxazole in addition to first-line drugs. The pharmacokinetic parameters of the population model were as follows (geometric mean ± standard deviation [SD]): metabolic clearance (CLm), 1.57 ± 3.71 liters/h; volume of distribution (V), 0.30 ± 0.05 liters · kg lean body mass(-1); drug clearance/creatinine clearance ratio (fr), 0.02 ± 0.13; gamma distribution rate constant (ktr_po), 2.18 ± 1.14; gamma distribution shape factor (n_po), 2.15 ± 0.39. The free fraction of sulfamethoxazole was 0.3, but ranged between 0.2 and 0.4. The median value of the MICs was 9.5 mg/liter (interquartile range [IQR], 4.75 to 9.5), and that of theƒAUC/MIC ratio was 14.3 (IQR, 13.0 to 17.5). The percentage of ƒT > MIC ranged between 43 and 100% of the dosing interval. The PK and PD data from this study are useful to explore a future dosing regimen of co-trimoxazole for MDR-TB treatment. (This study has been registered at ClinicalTrials.gov under registration no. NCT01832987.).