Rifampin pharmacokinetics in children, with and without human immunodeficiency virus infection, hospitalized for the management of severe forms of tuberculosis

Developmental Pharmacokinetics of Antibiotics Used in Neonatal ICU: Focus on Preterm Infants

Neonatal Infections are among the most common reasons for admission to the intensive care unit. Neonatal sepsis (NS) significantly contributes to mortality rates. Empiric antibiotic therapy of NS recommended by current international guidelines includes benzylpenicillin, ampicillin/amoxicillin, and aminoglycosides (gentamicin). The rise of antibacterial resistance precipitates the growth of the use of antibiotics of the Watch (second, third, and fourth generations of cephalosporines, carbapenems, macrolides, glycopeptides, rifamycins, fluoroquinolones) and Reserve groups (fifth generation of cephalosporines, oxazolidinones, lipoglycopeptides, fosfomycin), which are associated with a less clinical experience and higher risks of toxic reactions. A proper dosing regimen is essential for effective and safe antibiotic therapy, but its choice in neonates is complicated with high variability in the maturation of organ systems affecting drug absorption, distribution, metabolism, and excretion. Changes in antibiotic pharmacokinetic parameters result in altered efficacy and safety. Population pharmacokinetics can help to prognosis outcomes of antibiotic therapy, but it should be considered that the neonatal population is heterogeneous, and this heterogeneity is mainly determined by gestational and postnatal age. Preterm neonates are common in clinical practice, and due to the different physiology compared to the full terms, constitute a specific neonatal subpopulation. The objective of this review is to summarize the evidence about the developmental changes (specific for preterm and full-term infants, separately) of pharmacokinetic parameters of antibiotics used in neonatal intensive care units.

Global estimates and determinants of antituberculosis drug pharmacokinetics in children and adolescents: a systematic review and individual patient data meta-analysis

BACKGROUND

Suboptimal exposure to antituberculosis (anti-TB) drugs has been associated with unfavourable treatment outcomes. We aimed to investigate estimates and determinants of first-line anti-TB drug pharmacokinetics in children and adolescents at a global level.

METHODS

We systematically searched MEDLINE, Embase and Web of Science (1990-2021) for pharmacokinetic studies of first-line anti-TB drugs in children and adolescents. Individual patient data were obtained from authors of eligible studies. Summary estimates of total/extrapolated area under the plasma concentration-time curve from 0 to 24 h post-dose (AUC0-24) and peak plasma concentration (C max) were assessed with random-effects models, normalised with current World Health Organization-recommended paediatric doses. Determinants of AUC0-24 and C max were assessed with linear mixed-effects models.

RESULTS

Of 55 eligible studies, individual patient data were available for 39 (71%), including 1628 participants from 12 countries. Geometric means of steady-state AUC0-24 were summarised for isoniazid (18.7 (95% CI 15.5-22.6) h·mg·L-1), rifampicin (34.4 (95% CI 29.4-40.3) h·mg·L-1), pyrazinamide (375.0 (95% CI 339.9-413.7) h·mg·L-1) and ethambutol (8.0 (95% CI 6.4-10.0) h·mg·L-1). Our multivariate models indicated that younger age (especially <2 years) and HIV-positive status were associated with lower AUC0-24 for all first-line anti-TB drugs, while severe malnutrition was associated with lower AUC0-24 for isoniazid and pyrazinamide. N-acetyltransferase 2 rapid acetylators had lower isoniazid AUC0-24 and slow acetylators had higher isoniazid AUC0-24 than intermediate acetylators. Determinants of C max were generally similar to those for AUC0-24.

CONCLUSIONS

This study provides the most comprehensive estimates of plasma exposures to first-line anti-TB drugs in children and adolescents. Key determinants of drug exposures were identified. These may be relevant for population-specific dose adjustment or individualised therapeutic drug monitoring.

Four months of rifampicin monotherapy for latent tuberculosis infection in children

Diagnosing and treating latent tuberculosis infection (LTBI) is an important part of efforts to combat tuberculosis (TB). The Korean guidelines for TB published in 2020 recommend 2 LTBI regimens for children and adolescents: 9 months of daily isoniazid (9H) and 3 months of daily isoniazid plus rifampicin. Isoniazid for 6-12 months has been used to effectively treat LTBI in children for over 50 years. However, a long treatment period results in poor patient compliance. This review summarizes pediatric data on the treatment completion rate, safety, and efficacy of 4 months of daily rifampicin (4R) and evaluates the pharmacokinetics and pharmacodynamics of rifampicin in children. The 4R regimen has a higher treatment completion rate than the 9H regimen and equivalent safety in children. The efficacy of preventing TB is also consistent with that of 9H when summarizing reports published to date. A shorter treatment period could increase patient compliance and, therefore, prevent TB in more patients. By using an effective, safe, and highly compliant regimen for the treatment of children with LTBI, we would become one step closer to our goal of eradicating TB.

Optimizing dosing and fixed-dose combinations of rifampicin, isoniazid, and pyrazinamide in pediatric patients with tuberculosis: a prospective population pharmacokinetic study

BACKGROUND

In 2010, the WHO revised dosing guidelines for treatment of childhood tuberculosis. Our aim was to investigate first-line antituberculosis drug exposures under these guidelines, explore dose optimization using the current dispersible fixed-dose combination (FDC) table of rifampicin/isoniazid/pyrazinamide; 75/50/150 mg , and suggest a new FDC with revised weight-bands.

METHODS

Children with drug-susceptible tuberculosis in Malawi and South Africa underwent pharmacokinetic sampling while receiving first-line tuberculosis drugs as single formulations according the 2010 WHO recommended doses. Nonlinear mixed-effects modelling and simulation was used to design the optimal FDC and weight-band dosing strategy for achieving the pharmacokinetic targets based on literature-derived adult AUC0-24h for rifampicin (38.7-72.9) isoniazid (11.6-26.3) and pyrazinamide (233-429 mg∙h/L).

RESULTS

180 children (42% female; 13.9% HIV-infected; median [range] age 1.9 [0.22-12] years; weight 10.7 [3.20-28.8] kg) were administered 1, 2, 3, or 4 FDC tablets (rifampicin/isoniazid/pyrazinamide 75/50/150 mg) daily for 4-8, 8-12, 12-16, and 16-25 kg weight-bands, respectively. Rifampicin exposure (for weight and age) was up to 50% lower than in adults. Increasing the tablet number resulted in adequate rifampicin but relatively high isoniazid and pyrazinamide exposures. Administering 1, 2, 3, or 4 optimized FDC tablets (rifampicin/isoniazid/pyrazinamide 120/35/130 mg) to children <6, 6-13, 13-20 and 20-25 kg, and 0.5 tablet in <3-month-olds with immature metabolism, improved exposures to all three drugs.

CONCLUSION

Current pediatric FDC doses resulted in low rifampicin exposures. Optimal dosing of all drugs cannot be achieved with the current FDCs. We propose a new FDC formulation and revised weight-bands.

Pharmacokinetics of antiretroviral and tuberculosis drugs in children with HIV/TB co-infection: a systematic review

INTRODUCTION

Management of concomitant use of ART and TB drugs is difficult because of the many drug-drug interactions (DDIs) between the medications. This systematic review provides an overview of the current state of knowledge about the pharmacokinetics (PK) of ART and TB treatment in children with HIV/TB co-infection, and identifies knowledge gaps.

METHODS

We searched Embase and PubMed, and systematically searched abstract books of relevant conferences, following PRISMA guidelines. Studies not reporting PK parameters, investigating medicines that are not available any longer or not including children with HIV/TB co-infection were excluded. All studies were assessed for quality.

RESULTS

In total, 47 studies met the inclusion criteria. No dose adjustments are necessary for efavirenz during concomitant first-line TB treatment use, but intersubject PK variability was high, especially in children <3 years of age. Super-boosted lopinavir/ritonavir (ratio 1:1) resulted in adequate lopinavir trough concentrations during rifampicin co-administration. Double-dosed raltegravir can be given with rifampicin in children >4 weeks old as well as twice-daily dolutegravir (instead of once daily) in children older than 6 years. Exposure to some TB drugs (ethambutol and rifampicin) was reduced in the setting of HIV infection, regardless of ART use. Only limited PK data of second-line TB drugs with ART in children who are HIV infected have been published.

CONCLUSIONS

Whereas integrase inhibitors seem favourable in older children, there are limited options for ART in young children (<3 years) receiving rifampicin-based TB therapy. The PK of TB drugs in HIV-infected children warrants further research.

A Systematic Review on the Effect of HIV Infection on the Pharmacokinetics of First-Line Tuberculosis Drugs

Introduction

Contrasting findings have been published regarding the effect of human immunodeficiency virus (HIV) on tuberculosis (TB) drug pharmacokinetics (PK).

Objectives

The aim of this systematic review was to investigate the effect of HIV infection on the PK of the first-line TB drugs (FLDs) rifampicin, isoniazid, pyrazinamide and ethambutol by assessing all published literature.

Methods

Searches were performed in MEDLINE (through PubMed) and EMBASE to find original studies evaluating the effect of HIV infection on the PK of FLDs. The included studies were assessed for bias and clinical relevance. PK data were extracted to provide insight into the difference of FLD PK between HIV-positive and HIV-negative TB patients. This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement and its protocol was registered at PROSPERO (registration number CRD42017067250).

Results

Overall, 27 studies were eligible for inclusion. The available studies provide a heterogeneous dataset from which consistent results could not be obtained. In both HIV-positive and HIV-negative TB groups, rifampicin (13 of 15) and ethambutol (4 of 8) peak concentration (C_max) often did not achieve the minimum reference values. More than half of the studies (11 of 20) that included both HIV-positive and HIV-negative TB groups showed statistically significantly altered FLD area under the concentration–time curve and/or C_max for at least one FLD.

Conclusions

HIV infection may be one of several factors that reduce FLD exposure. We could not make general recommendations with respect to the role of dosing. There is a need for consistent and homogeneous studies to be conducted.

Noninvasive 11C-rifampin positron emission tomography reveals drug biodistribution in tuberculous meningitis

Tuberculous meningitis (TBM) is a devastating form of tuberculosis (TB), and key TB antimicrobials, including rifampin, have restricted brain penetration. A lack of reliable data on intralesional drug biodistribution in infected tissues has limited pharmacokinetic (PK) modeling efforts to optimize TBM treatments. Current methods to measure intralesional drug distribution rely on tissue resection, which is difficult in humans and generally limited to a single time point even in animals. In this study, we developed a multidrug treatment model in rabbits with experimentally induced TBM and performed serial noninvasive dynamic ¹¹C-rifampin positron emission tomography (PET) over 6 weeks. Area under the curve brain/plasma ratios were calculated using PET and correlated with postmortem mass spectrometry. We demonstrate that rifampin penetration into infected brain lesions is limited, spatially heterogeneous, and decreases rapidly as early as 2 weeks into treatment. Moreover, rifampin concentrations in the cerebrospinal fluid did not correlate well with those in the brain lesions. First-in-human ¹¹C-rifampin PET performed in a patient with TBM confirmed these findings. PK modeling predicted that rifampin doses (≥30 mg/kg) were required to achieve adequate intralesional concentrations in young children with TBM. These data demonstrate the proof of concept of PET as a clinically translatable tool to noninvasively measure intralesional antimicrobial distribution in infected tissues.

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.

Pharmacokinetics of First-Line Anti-Tubercular Drugs

Determining the optimal dosages of isoniazid, rifampicin, pyrazinamide and ethambutol in children is necessary to obtain therapeutic serum concentrations of these drugs. Revised dosages have improved the exposure of 1st line anti-tubercular drugs to some extent; there is still scope for modification of the dosages to achieve exposures which can lead to favourable outcome of the disease. High dose of rifampicin is being investigated in clinical trials in adults with some benefit; studies are required in children. Inter-individual pharmacokinetic variability and the effect of age, nutritional status, Human immunodeficiency virus (HIV) infection, acetylator genotype may need to be accounted for in striving for the dosages best suited for an individual.

Pharmacokinetic study of isoniazid and pyrazinamide in children: impact of age and nutritional status

OBJECTIVES

To evaluate pharmacokinetics of first-line antitubercular drugs, isoniazid (INH) and pyrazinamide (PZA), with revised WHO dosages and to assess its adequacy in relation to age and nutritional status.

DESIGN

Observational study.

SETTING

This study was conducted at Sarojini Naidu Medical College, Agra, and National Institute for Research in Tuberculosis, Chennai.

PATIENTS

40 subjects diagnosed with tuberculosis were registered in the study and started on daily first-line antitubercular regimen based on the revised WHO guidelines.

INTERVENTIONS

Blood samples were collected at 0, 2, 4, 6 and 8 hours from these subjects after 15 days of treatment for drug estimations.

MAIN OUTCOME MEASURE

The measurement of drug concentrations (maximum peak concentration (C_max) and area under the time -concentration curve (AUC_{0-8 hours})) for INH and PZA. Appropriate statistical methods were used to evaluate the impact of age and nutritional status on pharmacokinetic variables.

RESULTS

For INH, the difference in drug exposures in children <3 years (C_max 3.18 µg/mL and AUC_{0-8 hours}15.76 µg/mL hour) and children >3 years (C_max3.05 µg/mL and AUC_{0-8 hours} 14.37 µg/mL hour) was not significant (P=0.94, P=0.81, respectively). The drug levels in children with low body mass index (BMI) (C_max3.08 µg/mL; AUC_{0-8 hours}14.81 µg/mL hour) were also comparable with their normal counterparts (C_max3.09 µg/mL, P=0.99; AUC_{0-8 hours} 14.69 µg/mL hour, P=0.82). PZA drug exposures obtained in children less than 3 years (C_max29.22 µg/mL, AUC_{0-8 hours} 155.45 µg/mL hour) were significantly lower compared with drug levels in children above 3 years (C_max 37.12 µg/mL, P=0.03; AUC 202.63 µg/mL hour, P value=0.01). Children with low BMI had significantly lower drug concentrations (C_max 31.90 µg/mL, AUC_{0-8 hours}167.64 µg/mL hour) when compared with normal counterparts (C_max 37.60 µg/mL, P=0.02; AUC_{0-8 hours} 208.77 µg/mL hour, P=0.01).

CONCLUSIONS

The revised WHO drug dosages were found to be adequate for INH with respect to age and nutritional status, whereas PZA showed significantly lower drug levels in children <3 years and in malnourished children.

Pharmacokinetics of First-Line Drugs Among Children With Tuberculosis in Rural Tanzania

BACKGROUND

Dosing recommendations for treating childhood tuberculosis (TB) were revised by the World Health Organization, yet so far, pharmacokinetic studies that have evaluated these changes are relatively limited. We evaluated plasma drug concentrations of rifampicin (RIF), isoniazid (INH), pyrazinamide (PZA), and ethambutol (EMB) among children undergoing TB treatment in Tanzania when these dosing recommendations were being implemented.

METHODS

At the end of intensive-phase TB therapy, blood was obtained 2 hours after witnessed medication administration to estimate the peak drug concentration (C2h), measured using high-performance liquid chromatography or liquid chromatography-tandem mass spectrometry methods. Differences in median drug concentrations were compared on the basis of the weight-based dosing strategy using the Mann-Whitney U test. Risk factors for low drug concentrations were analyzed using multivariate regression analysis.

RESULTS

We enrolled 51 human immunodeficiency virus-negative children (median age, 5.3 years [range, 0.75-14 years]). The median C2hs were below the target range for each TB drug studied. Compared with children who received the "old" dosages, those who received the "revised" WHO dosages had a higher median C2h for RIF (P = .049) and PZA (P = .015) but not for INH (P = .624) or EMB (P = .143); however, these revised dosages did not result in the target range for RIF, INH, and EMB being achieved. A low starting dose was associated with a low C2h for RIF (P = .005) and PZA (P = .005). Malnutrition was associated with a low C2h for RIF (P = .001) and INH (P = .001).

CONCLUSIONS

Among this cohort of human immunodeficiency virus-negative Tanzanian children, use of the revised dosing strategy for treating childhood TB did not result in the target drug concentration for RIF, INH, or EMB being reached.

Evaluation of the Adequacy of WHO Revised Dosages of the First-Line Antituberculosis Drugs in Children with Tuberculosis Using Population Pharmacokinetic Modeling and Simulations

Optimal doses for antituberculosis (anti-TB) drugs in children have yet to be established. In 2010, the World Health Organization (WHO) recommended revised dosages of the first-line anti-TB drugs for children. Pharmacokinetic (PK) studies that investigated the adequacy of the WHO revised dosages to date have yielded conflicting results. We performed population PK modeling using data from one of these studies to identify optimal dosage ranges. Ghanaian children with tuberculosis on recommended therapy with rifampin (RIF), isoniazid (INH), pyrazinamide (PZA), and ethambutol (EMB) for at least 4 weeks had blood samples collected predose and at 1, 2, 4, and 8 hours postdose. Drug concentrations were determined by validated liquid chromatography-mass spectrometry methods. Nonlinear mixed-effects models were applied to describe the population PK of those drugs using MonolixSuite2016R1 (Lixoft, France). Bayesian estimation was performed, the correlation coefficient, bias, and precision between the observed and predicted areas under the concentration-time curve (AUCs) were calculated, and Bland-Altman plots were analyzed. The population PK of RIF and PZA was described by a one-compartment model and that for INH and EMB by a two-compartment model. Plasma maximum concentration (C_max) and AUC targets were based on published results for children from India. The lowest target values for pediatric TB patients were attainable at the WHO-recommended dosage schedule for RIF and INH, except for N-acetyltransferase 2 non-slow acetylators (rapid and intermediate acetylators) in the lower-weight bands. However, higher published adult targets were not attainable for RIF and INH. The targets were not achieved for PZA and EMB. (This study has been registered at ClinicalTrials.gov under identifier NCT01687504.).

Evaluation of the Adequacy of the 2010 Revised World Health Organization Recommended Dosages of the First-line Antituberculosis Drugs for Children: Adequacy of Revised Dosages of TB Drugs for Children

BACKGROUND

The World Health Organization recommended increased dosages of the first-line antituberculosis (anti-TB) drugs for children in 2010. We examined the frequency of and factors associated with low plasma maximum concentration (Cmax) of each drug in children treated with the revised dosages.

METHODS

Children on anti-TB therapy for at least 4 weeks underwent pharmacokinetic testing. Plasma Cmax below the lower limit of proposed reference range was considered low. Bivariate and multivariate analyses were used to examine the factors associated with low Cmax of each drug.

RESULTS

Of the 100 children, 58% were male, 50% HIV-infected and 49% younger than 5 years old. The median (interquartile range) Cmax was 5.9 (4.5-7.7) µg/mL for isoniazid, 6.5 (4.9-8.8) µg/mL for rifampin, 26.0 (21.2-33.4) µg/mL for pyrazinamide and 1.7 (0.9-2.7) µg/mL for ethambutol. There was a strong correlation between Cmax and AUC0-8h for all drugs. Low Cmax occurred in 9/100 (9.0%), 61/100 (61.0%), 17/97 (17.5%) and 60/97 (61.9%) for isoniazid, rifampin, pyrazinamide and ethambutol, respectively. In addition, 75/97 (77.3%) children had pyrazinamide Cmax < 35 µg/mL. Factors associated with low Cmax were NAT2 metabolizer phenotype status for isoniazid; height, dosage and HIV coinfection status for rifampin; height for pyrazinamide; and age, dosage and HIV coinfection status for ethambutol.

CONCLUSIONS

The high frequency of low rifampin and ethambutol Cmax in our study is consistent with emerging pharmacokinetic data in children treated according to the new WHO recommendations. Higher dosages than currently recommended especially for rifampin may be necessary in children.

Diagnosis and treatment of paediatric tuberculosis: An insight review

Tuberculosis (TB) is a major public health problem, invading all age groups world-wide. It is an opportunistic infection affecting the individuals alone or with co-infections. Childhood TB is a neglected aspect and a significant health problem in epidemic areas. It constitutes more than 20% of TB incidence. Pediatric TB exists in the shadow of adult TB. The clinicians concentrate on pulmonary manifestation of TB, whereas it is a major problem in both pulmonary and extra-pulmonary infections. The rate of infection with this disease is mostly associated with poverty, social disruption and human immunodeficiency virus (HIV) infection. The diagnosis of extra-pulmonary TB (EPTB) is more difficult than pulmonary TB (PTB). Delayed diagnosis and executive treatment contribute to increase in the mortality rate in endemic areas. This article provides the evidence-based simple and safe screening method, indicating rapid, highly sensitive and specific diagnostic tests for pulmonary and EPTB in children. The most important aspect of treatment is the correct course of anti-tubercular drugs. This review serves the purpose of quick reference for microbiologists, epidemiologists, academicians, students and researchers. It provides guidance regarding early diagnosis and treatment accuracy of pediatric TB.

Pharmacokinetics of the First-Line Antituberculosis Drugs in Ghanaian Children with Tuberculosis with or without HIV Coinfection

Although human immunodeficiency virus (HIV) coinfection is the most important risk factor for a poor antituberculosis (anti-TB) treatment response, its effect on the pharmacokinetics of the first-line drugs in children is understudied. This study examined the pharmacokinetics of the four first-line anti-TB drugs in children with TB with and without HIV coinfection. Ghanaian children with TB on isoniazid, rifampin, pyrazinamide, and ethambutol for at least 4 weeks had blood samples collected predose and at 1, 2, 4, and 8 hours postdose. Drug concentrations were determined by validated liquid chromatography-mass spectrometry methods and pharmacokinetic parameters calculated using noncompartmental analysis. The area under the concentration-time curve from 0 to 8 h (AUC0-8), maximum concentration (Cmax), and apparent oral clearance divided by bioavailability (CL/F) for each drug were compared between children with and without HIV coinfection. Of 113 participants, 59 (52.2%) had HIV coinfection. The baseline characteristics were similar except that the coinfected patients were more likely to have lower weight-for-age and height-for-age Z scores (P < 0.05). Rifampin, pyrazinamide, and ethambutol median body weight-normalized CL/F values were significantly higher, whereas the plasma AUC0-8 values were lower, in the coinfected children than in those with TB alone. In the multivariate analysis, drug dose and HIV coinfection jointly influenced the apparent oral clearance and AUC0-8 for rifampin, pyrazinamide, and ethambutol. Isoniazid pharmacokinetics were not different by HIV coinfection status. HIV coinfection was associated with lower plasma exposure of three of the four first-line anti-TB drugs in children. Whether TB/HIV-coinfected children need higher dosages of rifampin, pyrazinamide, and ethambutol requires further investigation. (This study has been registered at ClinicalTrials.gov under identifier NCT01687504.).

Pharmacokinetics of First-Line Antituberculosis Drugs Using WHO Revised Dosage in Children With Tuberculosis With and Without HIV Coinfection

BACKGROUND

Pharmacokinetic data on the first-line antituberculosis drugs using the World Health Organization (WHO) revised dosages for children are limited. We investigated the pharmacokinetics of these drugs in children who were mostly treated with revised dosages.

METHODS

Children with tuberculosis on first-line therapy for at least 4 weeks had blood samples collected at predose, 1, 2, 4, and 8 hours postdose. Drug concentrations were determined by validated liquid chromatography mass spectrometry methods, and pharmacokinetic parameters were calculated using noncompartmental analysis. Factors associated with plasma peak concentration (C_max) and the area under the time-concentration curve 0-8 hours (AUC_0-8h) of each drug was examined using univariate and multivariate analysis.

RESULTS

Of the 62 children, 32 (51.6%) were male, 29 (46.8%) were younger than 5 years old, and 28 (45.2%) had human immunodeficiency virus (HIV) coinfection. Three patients had undetectable pyrazinamide and ethambutol concentrations. The median (interquartile range) AUC_0-8h for isoniazid was 17.7 (10.2-23.4) µg·h mL^-1, rifampin was 26.0 (15.3-36.1) µg·h mL^-1, pyrazinamide was 144.6 (111.5-201.2) µg·h mL^-1, and ethambutol was 6.7 (3.8-10.4) µg·h mL^-1. Of the children who received recommended weight-band dosages, 44/51 (86.3%), 46/56 (82.1%), 27/56 (48.2%), and 21/51 (41.2%) achieved target C_max for isoniazid, pyrazinamide, ethambutol, and rifampin, respectively. In multivariate analysis, age, sex, HIV coinfection status, and drug dosage in milligrams per kilogram were associated with the drugs' plasma drug C_max or AUC_0-8h.

CONCLUSIONS

The revised dosages appeared to be adequate for isoniazid and pyrazinamide, but not for rifampin or ethambutol in this population. Higher dosages of rifampin and ethambutol than currently recommended may be required in most children.

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.

Low Serum Concentrations of Rifampicin and Pyrazinamide Associated with Poor Treatment Outcomes in Children with Tuberculosis Related to HIV Status

OBJECTIVES

To compare the pharmacokinetics of rifampicin (RMP), isoniazid (INH) and pyrazinamide (PZA) between HIV-infected and HIV-uninfected children with tuberculosis (TB) and correlate it with TB treatment outcome.

METHODS

HIV-uninfected (n = 84) and HIV-infected (n = 77) children with TB receiving standard thrice weekly treatment were recruited from 6 hospitals in India. Semi-intensive pharmacokinetic sampling was performed during intensive phase of TB treatment after directly observed administration of drugs. Drug concentrations were measured by high performance liquid chromatography. INH acetylator status was determined, and nutritional assessment was done. Children were followed-up and treatment outcomes noted.

RESULTS

Children with HIV and TB had significantly lower RMP peak concentration (Cmax) (2.6 vs. 5.1 μg/mL; P < 0.001) and exposure [area under the time-concentration curve (AUC0-8); 10.4 vs. 23.4 μg/mL h; P < 0.001] than those with TB. Among HIV-infected children, a significantly higher proportion had stunting (77% vs. 29%; P < 0.001) and underweight (73% vs. 38%; P < 0.001) compared with children with TB. Combining both groups, RMP Cmax (P = 0.001; adjusted odds ratio = 1.437; 95% confidence interval: 1.157-1.784) and PZA Cmax (P = 0.027; adjusted odds ratio = 1.041; 95% confidence interval: 1.005-1.079) significantly influenced treatment outcome.

CONCLUSIONS

HIV infection was associated with lower Cmax of RMP and INH and AUC0-8 of RMP. Over 90% of children in both groups had subtherapeutic RMP Cmax. Cmax of RMP and PZA significantly influenced TB treatment outcome in children with TB. The findings have important clinical implications and suggest the need to increase anti-TB drug doses in children with HIV and TB.

Pharmacokinetics of Rifampin, Isoniazid, Pyrazinamide, and Ethambutol in Infants Dosed According to Revised WHO-Recommended Treatment Guidelines

There are limited pharmacokinetic data for use of the first-line antituberculosis drugs during infancy (<12 months of age), when drug disposition may differ. Intensive pharmacokinetic sampling was performed in infants routinely receiving antituberculosis treatment, including rifampin, isoniazid, pyrazinamide, and ethambutol, using World Health Organization-recommended doses. Regulatory-approved single-drug formulations, including two rifampin suspensions, were used on the sampling day. Assays were conducted using liquid chromatography-mass spectrometry; pharmacokinetic parameters were generated using noncompartmental analysis. Thirty-nine infants were studied; 14 (36%) had culture-confirmed tuberculosis. Fifteen (38%) were premature (<37 weeks gestation); 5 (13%) were HIV infected. The mean corrected age and weight were 6.6 months and 6.45 kg, respectively. The mean maximum plasma concentrations (Cmax) for rifampin, isoniazid, pyrazinamide, and ethambutol were 2.9, 7.9, 41.9, and 1.3 μg/ml, respectively (current recommended adult target concentrations: 8 to 24, 3 to 6, 20 to 50, and 2 to 6 μg/ml, respectively), and the mean areas under the concentration-time curves from 0 to 8 h (AUC0-8) were 12.1, 24.7, 239.4, and 5.1 μg · h/ml, respectively. After adjusting for age and weight, rifampin exposures for the two formulations used differed inCmax(geometric mean ratio [GMR],2.55; 95% confidence interval [CI], 1.47 to 4.41;P= 0.001) and AUC0-8(GMR, 2.52; 95% CI, 1.34 to 4.73;P= 0.005). HIV status was associated with lower pyrazinamideCmax(GMR, 0.85; 95% CI, 0.75 to 0.96;P= 0.013) and AUC0-8(GMR, 0.79; 95% CI, 0.69 to 0.90;P< 0.001) values. No other important differences were observed due to age, weight, prematurity, ethnicity, or gender. In summary, isoniazid and pyrazinamide concentrations in infants compared well with proposed adult target concentrations; ethambutol concentrations were lower but similar to previously reported pediatric studies. The low rifampin exposures require further investigation. (This study has been registered at ClinicalTrials.gov under registration no. NCT01637558.).

Adequacy of Rifampin Absorption after Jejunostomy Tube Administration

It is not always possible to administer antituberculosis pharmacotherapy orally for reasons that may be a direct consequence of tuberculosis itself. To our knowledge, no published literature is available regarding antituberculosis drug absorption via feeding tube. We present the case of a patient with tuberculosis meningitis who required medication administration via percutaneous endoscopic jejunostomy (PEJ) tube. Blood samples were collected during the continuation phase of antituberculosis therapy, immediately before dose administration, and then at 1, 2, 4, and 6 hours after dose administration for quantification of serum rifampin concentrations. Assaying these concentrations by high‐pressure liquid chromatography demonstrated a peak serum rifampin level (C_max) of 18 μg/ml and total rifampin exposure (area under the curve from 0–6 hours [AUC_0–6]) of 50.1 μg/ml. These are high compared with rifampin C_max and AUC_0–6 values reported in patients after oral rifampin administration; C_max tends to range between 4.0–10.5 μg/ml and AUC_0–6 7.0–52.9 μg/ml after oral administration of 600 mg at steady state. Based on our patient's results, therefore, rifampin administered by PEJ tube appears to be well absorbed, with preservation of adequate C_max and AUC values. It is worth noting that this was in the context of drug administration in the fasted state. In the absence of any published evidence of adequate absorption via jejunal feeding tube in the nonfasted state, it would seem prudent to ensure that patients are fasted when rifampin is administered via PEJ tube, just as patients are when oral rifampin is administered. This report represents the first documented evidence, to our knowledge, of adequate rifampin absorption when administered via PEJ tube and provides important reassurance for health care providers, patients, and families facing similar clinical scenarios.

A simultaneous population pharmacokinetic analysis of rifampicin in Malawian adults and children

AIMS

Low rifampicin plasma concentrations can lead to treatment failure and increased risk of developing drug resistant tuberculosis. The objectives of this study were to characterize the population pharmacokinetics (popPK) of rifampicin in Malawian children and adults with tuberculosis, simulate exposures under revised WHO dosing guidelines that aim to reduce the risk of low exposures of rifampicin and examine predicted exposures using weight- and age-based dosing bands under new dosing recommendations.

METHODS

Patients were recruited at least two weeks after initiation of the intensive phase of treatment and received RIF in FDC of anti-TB drugs. A total of 5-6 rich and 1-2 sparse samples were collected. nonmem (v7.2) was used to build a population-PK model.

RESULTS

A 165 TB patients, 115 adults and 50 children, aged 7 months to 65 years and weighing 4.8 to 87 kg, were included in the one compartment model with first order absorption best described the data. The mean population estimate for CL/F was 23.9 (l h(-1)  70 kg(-1) ) with inter-individual variability of 46.6%. Exposure was unaffected by HIV status. Relative bioavailability in children was estimated at 49% lower compared to adults (100% relative bioavailability). Simulations showed significantly lower rifampicin exposure in children vs. adults. In children average AUC was 13.5 mg l(-1) h, which was nearly half that was observed in adults (26.3 mg l(-1)  h). Using age as a surrogate for weight in dosing bands gave similar results compared with the weight bands. Increasing dose to approximately 15 mg kg(-1) , increased AUC in children to an average of 22 mgl(-1)  h. bringing expected exposures in children closer to those predicted for adults.

CONCLUSION

The popPK model developed can be used to optimize rifampicin exposures through dosing simulations. WHO dosing recommendations may not be achieved using currently licensed fixed dose combination formulations of TB therapy.

Recommendations for treating children with drug-resistant tuberculosis

Tuberculosis (TB) is still one of the most difficult infectious diseases to treat, and the second most frequent cause of death due to infectious disease throughout the world. The number of cases of multidrug-resistant (MDR-TB) and extensively drug-resistant TB (XDR-TB), which are characterised by high mortality rates, is increasing. The therapeutic management of children with MDR- and XDR-TB is complicated by a lack of knowledge, and the fact that many potentially useful drugs are not registered for pediatric use and there are no formulations suitable for children in the first years of life. Furthermore, most of the available drugs are burdened by major adverse events that need to be taken into account, particularly in the case of prolonged therapy. This document describes the recommendations of a group of scientific societies on the therapeutic approach to pediatric MDR- and XDR-TB. On the basis of a systematic literature review and their personal clinical experience, the experts recommend that children with active TB caused by a drug-resistant strain of Mycobacterium tuberculosis should always be referred to a specialised centre because of the complexity of patient management, the paucity of pediatric data, and the high incidence of adverse events due to second-line anti-TB treatment.

A Critical Review of the Current Evidence for Measuring Drug Concentrations of First-Line Agents Used to Treat Tuberculosis in Children

Tuberculosis is a leading cause of infectious disease-related morbidity and mortality worldwide. Additionally, treatment is complex with most patients requiring combination therapy of first-line agents for multiple months. Children are especially at risk from the medications used to treat tuberculosis and therefore interventions to optimize both efficacy and safety are needed. Protocols exist for therapeutic drug monitoring in tuberculosis patients yet there is a gap in knowledge regarding the extent of any benefits achieved, especially in children. This review aims to summarize and evaluate literature reporting outcomes related to the measurement of drug concentrations of first-line agents used to treat tuberculosis (rifampin, isoniazid, pyrazinamide, ethambutol) in children. Findings showed a lack of strong evidence to support therapeutic drug monitoring in children with tuberculosis. Standard weight-based dosing of first-line agents does not commonly achieve target concentrations yet the effect on clinical outcomes remains unclear. As such, therapeutic drug monitoring should not be recommended currently as a widespread practice for all children with tuberculosis. However, future research should assess any benefit in special populations such as those with relapsing or recurrent disease, or those presenting with adverse drug reactions.

Pharmacokinetics of isoniazid, rifampicin, pyrazinamide and ethambutol in Indian children

BACKGROUND

The available pharmacokinetic data on anti-tubercular drugs in children raises the concern of suboptimal plasma concentrations attained when doses extrapolated from adult studies are used. Also, there is lack of consensus regarding the effect of malnutrition on pharmacokinetics of anti-tubercular drugs in children. We conducted this study with the aims of determining the plasma concentrations of isoniazid, rifampicin, pyrazinamide and ethambutol achieved with different dosage of the anti-tubercular drugs so as to provide supportive evidence to the revised dosages and to evaluate the effects of malnutrition on the pharmacokinetics of these drugs in children. We also attempted to correlate the plasma concentrations of these drugs with clinical outcome of therapy.

METHOD

Prospective drug estimation study was conducted in two groups of children, age 6 months to 15 years, with tuberculosis, with or without severe malnutrition, receiving different dosage of daily anti- tubercular therapy. The dosage (range) of isoniazid was 5 (4-6) and 10 (7-15) mg/kg in the two groups, respectively, that of rifampicin-10 (8-12) and 15 (10-12) mg/kg, respectively, both the groups received same dose of pyrazinamide (30-35 mg/kg) and ethambutol (20-25 mg/kg). All four drugs were simultaneously estimated by liquid chromatography-mass spectrometry (LC-MS/MS).

RESULTS AND CONCLUSION

The median (IQR) Cmax of isoniazid increased significantly from 0.6 (0.3,1.2) μg/mL to 3.4 (1.8, 5.0) μg/mL with increase in the dose. Plasma rifampicin concentrations increased only marginally on increasing the dose [median (IQR) Cmax: 10.4 (7.2, 13.9) μg/mL vs. 12.0 (6.1, 24.3) μg/mL, p=0.08]. For ethambutol, 55.9% of the children had inadequate 2-hour concentrations. Two-hour plasma concentrations of at least one drug were low in 59 (92.2%) and 54 (85.7%) children in the two dosing regimen, respectively. We did not observe any effect of malnutrition on pharmacokinetic parameters of the drugs studied. We did not observe an association between low plasma drug concentrations and poor outcome. We may have to be cautious while increasing the doses and strive to asses other factors influencing the drug concentrations and treatment outcomes in children.

Pharmacokinetics of anti-TB drugs in Malawian children: reconsidering the role of ethambutol

Background

Current guidelines for dosing of anti-TB drugs in children advocate higher doses for rifampicin and isoniazid despite limited availability of paediatric data on the pharmacokinetics of these drugs, especially from Africa, where the burden of childhood disease remains high.

Methods

Thirty children aged 6 months to 15 years underwent intensive pharmacokinetic sampling for first-line anti-TB drugs at Queen Elizabeth Central Hospital, Blantyre, Malawi. Rifampicin, isoniazid, pyrazinamide and ethambutol were dosed at 10, 5, 25 and 20 mg/kg, respectively. Plasma drug concentrations were determined using sensitive, validated bioanalytical methods and summary pharmacokinetic parameters were estimated using non-compartmental analysis.

Results

The median (IQR) C_max was 2.90 (2.08–3.43), 3.37 (2.55–4.59), 34.60 (32.30–40.90) and 1.20 (0.85–1.68) mg/L while the median (IQR) AUC_0–∞ was 16.92 (11.10–22.74), 11.48 (7.35–18.93), 333.50 (279.50–487.2) and 8.65 (5.96–11.47) mg·h/L for rifampicin, isoniazid, pyrazinamide and ethambutol, respectively. For all drugs, pharmacokinetic parameters relating to drug absorption and exposure were lower than those published for adults, though similar to existing paediatric data from sub-Saharan Africa. Weight and/or dose predicted at least one measure of exposure for all drugs. Age-related decreases in CL/F for rifampicin and pyrazinamide and a biphasic elimination pattern of isoniazid were observed. Predicted AUC_0–∞ for rifampicin dosed at 15 mg/kg was comparable to that of adults while the dose required to achieve ethambutol exposure similar to that in adults was 55 mg/kg or higher.

Conclusions

These data support recently revised WHO recommendations for dosing of anti-TB drugs in children, but dosing of ethambutol in children also appears inadequate by comparison with adult pharmacokinetic data.

Pharmacokinetics of first-line antituberculosis drugs in HIV-infected children with tuberculosis treated with intermittent regimens in India

The objective of this report was to study the pharmacokinetics of rifampin (RMP), isoniazid (INH), and pyrazinamide (PZA) in HIV-infected children with tuberculosis (TB) treated with a thrice-weekly anti-TB regimen in the government program in India. Seventy-seven HIV-infected children with TB aged 1 to 15 years from six hospitals in India were recruited. During the intensive phase of TB treatment with directly observed administration of the drugs, a complete pharmacokinetic study was performed. Drug concentrations were measured by high-performance liquid chromatography. A multivariable regression analysis was done to explore the factors impacting drug levels and treatment outcomes. The proportions of children with subnormal peak concentrations (Cmax) of RMP, INH, and PZA were 97%, 28%, and 33%, respectively. Children less than 5 years old had a lower median Cmax and lower exposure (area under the time-concentration curve from 0 to 8 h [AUC0-8]) of INH (Cmax, 2.5 versus 5.1 μg/ml, respectively [P=0.016]; AUC0-8, 11.1 versus 22.0 μg/ml·h, respectively [P=0.047[) and PZA (Cmax, 34.1 versus 42.3 μg/ml, respectively [P=0.055]; AUC0-8, 177.9 versus 221.7 μg/ml·h, respectively [P=0.05]) than those more than 5 years old. In children with unfavorable versus favorable outcomes, the median Cmax of RMP (1.0 versus 2.8 μg/ml, respectively; P=0.002) and PZA (31.9 versus 44.4 μg/ml, respectively; P=0.045) were significantly lower. Among all factors studied, the PZA Cmax influenced TB treatment outcome (P=0.011; adjusted odds ratio, 1.094; 95% confidence interval, 1.021 to 1.173). A high proportion of children with HIV and TB had a subnormal RMP Cmax. The PZA Cmax significantly influenced treatment outcome. These findings have important clinical implications and emphasize that drug doses in HIV-infected children with TB have to be optimized.

Pharmacokinetics and safety of moxifloxacin in children with multidrug-resistant tuberculosis

BACKGROUND

Moxifloxacin is currently recommended at a dose of 7.5-10 mg/kg for children with multidrug-resistant (MDR) tuberculosis, but pharmacokinetic and long-term safety data of moxifloxacin in children with tuberculosis are lacking. An area under the curve (AUC) of 40-60 µg × h/mL following an oral moxifloxacin dose of 400 mg has been reported in adults.

METHODS

In a prospective pharmacokinetic and safety study, children 7-15 years of age routinely receiving moxifloxacin 10 mg/kg daily as part of multidrug treatment for MDR tuberculosis in Cape Town, South Africa, for at least 2 weeks, underwent intensive pharmacokinetic sampling (predose and 1, 2, 4, 8, and either 6 or 11 hours) and were followed for safety. Assays were performed using liquid chromatography-tandem mass spectrometry, and pharmacokinetic measures calculated using noncompartmental analysis.

RESULTS

Twenty-three children were included (median age, 11.1 years; interquartile range [IQR], 9.2-12.0 years); 6 of 23 (26.1%) were human immunodeficiency virus (HIV)-infected. The median maximum serum concentration (Cmax), area under the curve from 0-8 hours (AUC0-8), time until Cmax (Tmax), and half-life for moxifloxacin were 3.08 (IQR, 2.85-3.82) µg/mL, 17.24 (IQR, 14.47-21.99) µg × h/mL, 2.0 (IQR, 1.0-8.0) h, and 4.14 (IQR, 3.45-6.11), respectively. Three children, all HIV-infected, were underweight for age. AUC0-8 was reduced by 6.85 µg × h/mL (95% confidence interval, -11.15 to -2.56) in HIV-infected children. Tmax was shorter with crushed vs whole tablets (P = .047). Except in 1 child with hepatotoxicity, all adverse effects were mild and nonpersistent. Mean corrected QT interval was 403 (standard deviation, 30) ms, and no prolongation >450 ms occurred.

CONCLUSIONS

Children 7-15 years of age receiving moxifloxacin 10 mg/kg/day as part of MDR tuberculosis treatment have low serum concentrations compared with adults receiving 400 mg moxifloxacin daily. Higher moxifloxacin dosages may be required in children. Moxifloxacin was well tolerated in children treated for MDR tuberculosis.

Full-gene sequencing analysis of NAT2 and its relationship with isoniazid pharmacokinetics in Venezuelan children with tuberculosis

BACKGROUND

Genetic variants in NAT2 are associated with pharmacokinetic variation of isoniazid, the cornerstone of antituberculosis treatment. We investigated the acetylator genotype and phenotype in children on antituberculosis treatment that were previously shown to have low plasma isoniazid levels.

MATERIALS & METHODS

NAT2 genotyping and phenotyping, represented as metabolic ratio of acetylisoniazid over isoniazid and as isoniazid half-life, were performed in 30 Venezuelan children.

RESULTS

Most children carried genotypes resulting in an intermediate or low enzyme activity (43 and 40%, respectively). Isoniazid exposure differed between genotypically slow and rapid acetylators (13.3 vs 4.5 h×mg/l, p < 0.01). Both the metabolic ratio as well as the half-life of isoniazid distinguished genotypically slow from genotypically rapid or intermediate acetylators (all p ≤ 0.01).

CONCLUSION

In Venezuelan children a clear difference in isoniazid pharmacokinetics and acetylator phenotype between genotypically slow and genotypically intermediate or rapid acetylating children was observed. Original submitted 31 July 2013; Revision submitted 11 November 2013.

Acquired drug resistance during inadequate therapy in a young child with tuberculosis

Drug resistance in children with tuberculosis is usually primary (transmitted); however, resistance acquisition during treatment is possible. We describe a child with tuberculosis who acquired drug resistance while receiving directly observed but inadequate first-line therapy and the programmatic and clinical factors that may have contributed to resistance acquisition.

Understanding pharmacokinetics to improve tuberculosis treatment outcome

INTRODUCTION

Tuberculosis (TB) remains the leading cause of death from a curable infectious disease; drug-resistant TB threatens to dismantle all prior gains in global control. Suboptimal circulating anti-TB drug concentrations can lead to lack of cure and acquired drug resistance.

AREAS COVERED

This review will introduce pharmacokinetic parameters for key anti-TB drugs, as well as the indications and limitations of measuring these parameters in clinical practice. Current and novel methodologies for delivering anti-TB pharmacokinetic-pharmacodynamic data are highlighted and gaps in operational research described.

EXPERT OPINION

Individual pharmacokinetic variability is commonplace, underappreciated and difficult to predict without therapeutic drug monitoring (TDM). Pharmacokinetic thresholds associated with poor TB treatment outcome in drug-susceptible TB have recently been described and may now guide the application of TDM, but require validation in a variety of settings and comorbidities. Dried blood spots for TDM and prepackaged multidrug plates for minimum inhibitory concentration testing will overcome barriers of accessibility and represent areas for innovation. Operationalizing pharmacokinetics has the potential to improve TB outcomes in the most difficult-to-treat forms of the disease such as multidrug resistance. Clinical studies in these areas are eagerly anticipated and we expect will better define the rational introduction of novel therapeutics.

Population pharmacokinetics of rifampicin, pyrazinamide and isoniazid in children with tuberculosis: in silico evaluation of currently recommended doses

OBJECTIVES

To describe the population pharmacokinetics of rifampicin, pyrazinamide and isoniazid in children and evaluate the adequacy of steady-state exposures.

PATIENTS AND METHODS

We used previously published data for 76 South African children with tuberculosis to describe the population pharmacokinetics of rifampicin, pyrazinamide and isoniazid. Monte Carlo simulations were used to predict steady-state exposures in children following doses in fixed-dose combination tablets in accordance with the revised guidelines. Reference exposures were derived from an ethnically similar adult population with tuberculosis taking currently recommended doses.

RESULTS

The final models included allometric scaling of clearance and volume of distribution using body weight. Maturation was included for clearance of isoniazid and clearance and absorption transit time of rifampicin. For a 2-year-old child weighing 12.5 kg, the estimated typical oral clearances of rifampicin and pyrazinamide were 8.15 and 1.08 L/h, respectively. Isoniazid typical oral clearance (adjusted for bioavailability) was predicted to be 4.44, 11.6 and 14.6 L/h for slow, intermediate and fast acetylators, respectively. Higher oral clearance values in intermediate and fast acetylators also resulted from 23% lower bioavailability compared with slow acetylators.

CONCLUSIONS

Simulations based on our models suggest that with the new WHO dosing guidelines and utilizing available paediatric fixed-dose combinations, children will receive adequate rifampicin exposures when compared with adults, but with a larger degree of variability. However, pyrazinamide and isoniazid exposures in many children will be lower than in adults. Further studies are needed to confirm these findings in children administered the revised dosages and to optimize pragmatic approaches to dosing.

Mycobacterium ulcerans disease: experience with primary oral medical therapy in an Australian cohort

Background

Mycobacterium ulcerans (MU) is responsible for disfiguring skin lesions and is endemic on the Bellarine peninsula of southeastern Australia. Antibiotics have been shown to be highly effective in sterilizing lesions and preventing disease recurrences when used alone or in combination with surgery. Our practice has evolved to using primarily oral medical therapy.

Methods

From a prospective cohort of MU patients managed at Barwon Health, we describe those treated with primary medical therapy defined as treatment of a M. ulcerans lesion with antimicrobials either alone or in conjunction with limited surgical debridement.

Results

From 1/10/2010 through 31/12/11, 43 patients were treated with exclusive medical therapy, of which 5 (12%) also underwent limited surgical debridement. The median patient age was 50.2 years, and 86% had WHO category 1 and 91% ulcerative lesions. Rifampicin was combined with ciprofloxacin in 30 (70%) and clarithromycin in 12 (28%) patients. The median duration of antibiotic therapy was 56 days, with 7 (16%) receiving less than 56 days. Medication side effects requiring cessation of one or more antibiotics occurred in 7 (16%) patients. Forty-two (98%) patients healed without recurrence within 12 months, and 1 patient (2%) experienced a relapse 4 months after completion of 8 weeks of antimicrobial therapy.

Conclusion

Our experience demonstrates the efficacy and safety of primary oral medical management of MU infection with oral rifampicin-based regimens. Further research is required to determine the optimal and minimum durations of antibiotic therapy, and the most effective antibiotic dosages and formulations for young children.

Mycobacterium ulcerans (MU) is responsible for disfiguring skin infections which are challenging to treat. The recommended treatment for MU has continued to evolve from surgery to remove all involved tissue, to the use of effective combination oral antibiotics with surgery as required. Our study describes the oral medical treatment utilised for consecutive cases of MU infection over a 15 month period at our institution, in Victoria, Australia. Managing patients primarily with oral antibiotics results in high cure rates and excellent cosmetic outcomes. The success with medical treatment reported in this study will aid those treating cases of MU infection, and will add to the growing body of knowledge about the relative roles of antibiotics and surgery for treating this infection.

Assessment of juvenile pigs to serve as human pediatric surrogates for preclinical formulation pharmacokinetic testing

Pediatric drug development is hampered by biological, clinical, and formulation challenges associated with age-based populations. A primary cause for this lack of development is the inability to accurately predict ontogenic changes that affect pharmacokinetics (PK) in children using traditional preclinical animal models. In response to this issue, our laboratory has conducted a proof-of-concept study to investigate the potential utility of juvenile pigs to serve as surrogates for children during preclinical PK testing of selected rifampin dosage forms. Pigs were surgically modified with jugular vein catheters that were externalized in the dorsal scapular region and connected to an automated blood sampling system (PigTurn-Culex-L). Commercially available rifampin capsules were administered to both 20 and 40 kg pigs to determine relevant PK parameters. Orally disintegrating tablet formulations of rifampin were also developed and administered to 20 kg pigs. Plasma samples were prepared from whole blood by centrifugation and analyzed for rifampin content by liquid chromatography-tandem mass spectrometry. Porcine PK parameters were determined from the resultant plasma-concentration time profiles and contrasted with published rifampin PK data in human adults and children. Results indicated significant similarities in dose-normalized absorption and elimination parameters between pigs and humans. Moreover, ontogenic changes observed in porcine PK parameters were consistent with ontogenic changes reported for human PK. These results demonstrate the potential utility of the juvenile porcine model for predicting human pediatric PK for rifampin. Furthermore, utilization of juvenile pigs during formulation testing may provide an alternative approach to expedite reformulation efforts during pediatric drug development.

Nutritional status and its response to treatment of children, with and without HIV infection, hospitalized for the management of tuberculosis

BACKGROUND

The association of childhood tuberculosis (TB) and malnutrition is known, but treatment response, the influence of the acute-phase response (APR) and concomitant HIV infection are not well documented.

AIM

To evaluate the nutritional response and APR in HIV-infected and uninfected children hospitalised for the treatment of TB and receiving standard anti-tuberculosis chemotherapy.

METHODS

During a study of the pharmacokinetics of standard anti-tuberculosis agents, anthropometric parameters were measured and blood concentrations of nutrients and C-reactive protein (CRP) determined at 1 and 4 months after initiation of chemotherapy.

RESULTS

24 HIV-infected and 34 HIV-uninfected children were studied. On enrollment, 31.6% of HIV-infected and 2.9% of HIV-uninfected children were underweight, and 31.6% and 14.7%, respectively, were stunted. Mean values of weight, height/length, head circumference and mid-upper-arm circumference on enrollment and at 4-month assessment in HIV-infected and uninfected children did not differ. Mean triceps skinfold (TSF) (8.17 and 9.73 cm) and subscapular skinfold (SSF) thicknesses (5.75 and 7.5 cm) on enrollment differed significantly (P = 0.03 and P = 0.003); by 4 months, TSF had declined to 5.97 cm (P<0.001) and 8.87 cm (P = 0.05), respectively, and SSF to 5.57 cm (P = 0.79) and 6.73 cm (P = 0.04); the arm muscle area (AMA) was low in a majority of children on enrollment and remained so at the second assessment. CRP was raised in 66.6% and 53.3% of HIV-infected and -uninfected children on enrollment, but at 4-month assessment was raised in 63.2% and 15.2%, respectively. Other micronutrient and haematological findings probably reflect an APR, but no children had sub-normal zinc or magnesium values; most selenium and vitamin C and E values were normal. An elevated platelet count (> 420 × 10(9)/L) was significantly more common in HIV-uninfected children, and was still raised in 39% at 4 months.

CONCLUSION

A majority of HIV-infected and uninfected children had an APR but it had resolved by 4 months in most HIV-uninfected children. In both groups, low and declining skinfolds and a persistently low AMA indicate a persistent disturbance of fat and protein metabolism, despite successful chemotherapy.

Management of children exposed to multidrug-resistant Mycobacterium tuberculosis

Children exposed to multidrug-resistant (MDR) Mycobacterium tuberculosis are at risk of developing MDR tuberculosis. Where treatment is available, it is lengthy, expensive, and associated with poor adherence and notable morbidity and mortality. Preventive treatment effectively lowers the risk of disease progression for contacts of individuals with drug-susceptible tuberculosis, but this strategy is poorly studied for contacts of people with MDR tuberculosis. In this Review we discuss the management of child contacts of source cases with MDR tuberculosis. We pay particular attention to assessment, existing international guidelines, possible preventive treatments, rationales for different management strategies, and the interaction with and implications of HIV infection.

Paediatric use of second-line anti-tuberculosis agents: a review

Childhood multidrug-resistant tuberculosis (MDR-TB) is an emerging global epidemic. With the imminent roll-out of rapid molecular diagnostic tests, more children are likely to be identified and require treatment. As MDR-TB is resistant to the most effective first-line drugs, clinicians will have to rely on second-line medications which are less effective and often associated with more pronounced adverse effects than first-line therapy. Despite the fact that most of these agents were discovered many years ago, robust information is lacking regarding their pharmacokinetic and pharmacodynamic properties, adverse effects and drug interactions, especially in children. Children differ from adults in the way that drugs are administered, the manner in which they are metabolised and in the adverse effects experienced. The interaction of these drugs with human immunodeficiency virus infection and antiretroviral therapy is also poorly documented. This article reviews the available second-line drugs currently used in the treatment of MDR-TB in children and discusses medication properties and adverse effects while potential interactions with antiretroviral therapy are explored.

Pharmacokinetics of isoniazid, rifampin, and pyrazinamide in children younger than two years of age with tuberculosis: evidence for implementation of revised World Health Organization recommendations

The World Health Organization (WHO) recently issued revised first-line antituberculosis (anti-TB) drug dosage recommendations for children. No pharmacokinetic studies for these revised dosages are available for children <2 years. The aim of the study was to document the pharmacokinetics of the first-line anti-TB agents in children <2 years of age comparing previous and revised WHO dosages of isoniazid (INH; 5 versus 10 mg/kg/day), rifampin (RMP; 10 versus 15 mg/kg/day), and pyrazinamide (PZA; 25 versus 35 mg/kg/day) and to investigate the effects of clinical covariates, including HIV coinfection, nutritional status, age, gender, and type of tuberculosis (TB), and the effect of NAT2 acetylator status. Serum INH, PZA, and RMP levels were prospectively assessed in 20 children <2 years of age treated for TB following the previous and the revised WHO dosage recommendations. Samples were taken prior to dosing and at 0.5, 1.5, 3, and 5 h following dosing. The maximum drug concentration in serum (C(max)), the time to C(max) (t(max)), and the area under the concentration-time curve (AUC) were calculated. Eleven children had pulmonary and 9 had extrapulmonary TB. Five were HIV infected. The mean C(max) (μg/ml) following the administration of previous/revised dosages were as follows: INH, 3.19/8.11; RMP, 6.36/11.69; PZA, 29.94/47.11. The mean AUC (μg·h/ml) were as follows: INH, 8.09/20.36; RMP, 17.78/36.95; PZA, 118.0/175.2. The mean C(max) and AUC differed significantly between doses. There was no difference in the t(max) values achieved. Children less than 2 years of age achieve target concentrations of first-line anti-TB agents using revised WHO dosage recommendations. Our data provided supportive evidence for the implementation of the revised WHO guidelines for first-line anti-TB therapy in young children.

Pharmacokinetics of anti-tuberculosis drugs in children

Tuberculosis (TB) is among the top 10 causes of death among children worldwide. Recent reports suggest that the currently recommended dosages of first-line anti-TB drugs are not adequate in children, particularly younger children. The objective of this review was to synthesize available pharmacokinetic data of anti-TB drugs in children from different settings that would help determine optimal doses of anti-TB drugs, in order to provide evidence-based recommendations. A PubMed database was searched from 1970 to present using the terms rifampicin, isoniazid, pyrazinamide, ethambutol, pharmacokinetics, HIV, TB, nutrition and children. References from identified articles were also reviewed and abstract from recent meetings were included. Available pharmacokinetic data from different settings suggest that age, nutritional status, HIV infection and gene polymorphisms in drug metabolising enzymes could significantly influence the pharmacokinetics of first-line anti-TB drugs. However, most of the pharmacokinetic studies conducted so far in children have failed to associate drug concentrations with treatment outcomes. Hence, more studies to examine the relationship between drug pharmacokinetics and response to anti-TB treatment are required. Studies to examine the impact of nutritional status and HIV infection on the pharmacokinetics of anti-TB drugs in children are needed.

The pharmacokinetics and pharmacodynamics of rifampicin in adults and children in relation to the dosage recommended for children

The dosages of antituberculosis agents recommended for treatment of childhood tuberculosis often reflect those for adult patients with similar mg/kg body weight dosages and ranges advised. Literature relating to the pharmacokinetics and pharmacodynamics of rifampicin (RMP) is reviewed and the serum concentrations reached by adults, both patients and healthy volunteers and children, established or not established on RMP, compared. Straight line regression of maximum RMP serum concentrations (C(max)) on dosage, weighted for the number of individuals, found slopes (SE) of 1.025 (0.067) and 0.881 (0.046) respectively for adult volunteers not established and established on RMP (P = 0.076), and similarly 0.748 (0.057) and 0.684 (0.038) respectively for adult patients (P < 0.001) and 0.622 (0.050) and 0.368 (0.041) respectively for children (P < 0.001). These results indicate that for equivalent RMP dosages adult patients reach a lower C(max) than adult volunteers and that adults, both volunteers and patients established on RMP reach higher C(max) values than children; children established on RMP require approximately twice the mg/kg body weight dosage of RMP to reach serum concentrations equivalent to those of adults. It is noteworthy that many adult patients receiving currently recommended RMP dosages also do not reach the often recommended RMP 2 h serum concentration of 8 μg/mL.

Treatment of paediatric TB: revised WHO guidelines

The World Health Organization has recently revised the recommended dosages of the main first-line anti-tuberculosis drugs for use in children. The recommended dosages and range of isoniazid, rifampicin, pyrazinamide and ethambutol have been increased from the previous recommended dosages. Ethambutol is now recommended for use in children of all ages including those of less than 5 years of age. This review explains the rationale for these recent revisions. Children require higher dosages than adults to achieve the same serum concentrations. Available data in HIV-uninfected children suggest that the revised dosages are within limits that have a very low risk of toxicity. An important challenge will be to examine the impact of higher dosages on clinical response, drug-drug interactions and risk of toxicity in HIV-infected children.

Changing trends in childhood tuberculosis

Several changes have been observed in the epidemiology, clinical manifestations, diagnostic modalities and treatment of tuberculosis. Emergence of HIV epidemic and drug resistance have posed significant challenges. With increase in the number of diseased adults and spread of HIV infection, the infection rates in children are likely to increase. It is estimated that in developing countries, the annual risk of tuberculosis infection in children is 2.5%. Nearly 8-20% of the deaths caused by tuberculosis occur in children. Extra pulmonary tuberculosis has increased over last two decades. HIV infected children are at an increased risk of tuberculosis, particularly disseminated disease. In last two decades, drug resistant tuberculosis has increased gradually with emergence of MDR and XDR-TB. The rate of drug resistance to any drug varied from 20% to 80% in different geographic regions. Significant changes have occurred in TB diagnostics. Various diagnostic techniques such as fluorescence LED microscopy, improved culture techniques, antigen detection, nucleic acid amplification, line probe assays and IGRAs have been developed and evaluated to improve diagnosis of childhood tuberculosis. Serodiagnosis is an attractive investigation but till date none of the tests have desirable sensitivity and specificity. Tests based on nucleic acid amplification are a promising advance but relatively less experience in children, need for technical expertise and high cost are limiting factors for their use in children with tuberculosis. Short-course chemotherapy for childhood tuberculosis is well established. Directly observed treatment strategy (DOTS) have shown encouraging result. DOTS plus strategy has been introduced for MDR TB.

Pyrazinamide plasma concentrations in young children with tuberculosis

Pyrazinamide plasma concentrations were determined in 34 children (median age, 3.32 years) 1 month after commencing antituberculosis treatment. The median (interquartile range) peak concentration was 30.7 (25.5, 35.0) mg/L after a median dose of 23 mg/kg. Peak concentrations < 20 mg/L were found in 5 children (15%) and such low concentrations were particularly likely after doses < 20 mg/kg.

Childhood tuberculosis: an emerging and previously neglected problem

Although awareness is growing, childhood tuberculosis (TB) remains a neglected disease in many resource-limited settings. In part this reflects operational difficulties, lack of visibility in official reports, as well as perceptions that children tend to develop mild disease, contribute little to disease transmission, and do not affect epidemic control. At an international level there is greater appreciation that children contribute significantly to the global TB disease burden and suffer severe TB-related morbidity and mortality, particularly in TB-endemic areas, where the disease often remains undiagnosed. However, this is not always the case at the national or local level and there remains an urgent need for feasible and implementable policies to guide clinical practice. Pediatric TB can be regarded as an emerging epidemic in areas where the adult epidemic remains out of control and Mycobacterium tuberculosis transmission is ongoing. This article reviews important concepts, challenges, and management principles related to childhood TB; it also summarizes the main priorities for future research.