Pharmacokinetics and Optimal Dosing of Levofloxacin in Children for Drug-Resistant Tuberculosis: An Individual Patient Data Meta-Analysis.

BACKGROUND: Each year 25 000-32 000 children develop rifampicin- or multidrug-resistant tuberculosis (RR/MDR-TB), and many more require preventive treatment. Levofloxacin is a key component of RR/MDR-TB treatment and prevention, but the existing pharmacokinetic data in children have not yet been comprehensively summarized. We aimed to characterize levofloxacin pharmacokinetics through an individual patient data meta-analysis of available studies and to determine optimal dosing in children. METHODS: Levofloxacin concentration and demographic data were pooled from 5 studies and analyzed using nonlinear mixed effects modeling. Simulations were performed using current World Health Organization (WHO)-recommended and model-informed optimized doses. Optimal levofloxacin doses were identified to target median adult area under the time-concentration curve (AUC)24 of 101 mg·h/L given current standard adult doses. RESULTS: Data from 242 children (2.8 years [0.2-16.8] was used). Apparent clearance was 3.16 L/h for a 13-kg child. Age affected clearance, reaching 50% maturation at birth and 90% maturation at 8 months. Nondispersible tablets had 29% lower apparent oral bioavailability compared to dispersible tablets. Median exposures at current WHO-recommended doses were below the AUC target for children weighing <24 kg and under <10 years, resulting in approximately half of the exposure in adults. Model-informed doses of 16-33 mg/kg for dispersible tablets or 16-50 mg/kg for nondispersible tablets were required to meet the AUC target without significantly exceeding the median adult Cmax. CONCLUSIONS: Revised weight-band dosing guidelines with doses of >20 mg/kg are required to ensure adequate exposure. Further studies are needed to determine safety and tolerability of these higher doses.

Pharmacokinetics and cardiac safety of clofazimine in children with rifampicin-resistant tuberculosis.

Clofazimine is recommended for the treatment of rifampicin-resistant tuberculosis (RR-TB), but there is currently no verified dosing guideline for its use in children. There is only limited safety and no pharmacokinetic (PK) data available for children. We aimed to characterize clofazimine PK and its relationship with QT-interval prolongation in children. An observational cohort study of South African children <18 years old routinely treated for RR-TB with a clofazimine-containing regimen was analyzed. Clofazimine 100 mg gelatin capsules were given orally once daily (≥20 kg body weight), every second day (10 to <20 kg), or thrice weekly (<10 kg). PK sampling and electrocardiograms were completed pre-dose and at 1, 4, and 10 hours post-dose, and the population PK and Fridericia-corrected QT (QTcF) interval prolongation were characterized. Fifty-four children contributed both PK and QTcF data, with a median age (2.5th-97.5th centiles) of 3.3 (0.5-15.6) years; five children were living with HIV. Weekly area under the time-concentration curve at steady state was 79.1 (15.0-271) mg.h/L compared to an adult target of 60.9 (56.0-66.6) mg.h/L. Children living with HIV had four times higher clearance compared to those without. No child had a QTcF ≥500 ms. A linear concentration-QTcF relationship was found, with a drug effect of 0.05 (0.027, 0.075) ms/µg/L. In some of the first PK data in children, we found clofazimine exposure using an off-label dosing strategy was higher in children versus adults. Clofazimine concentrations were associated with an increase in QTcF, but severe prolongation was not observed. More data are required to inform dosing strategies in children.

POINT-OF-CARE ULTRASOUND FOR TUBERCULOSIS IN YOUNG CHILDREN WITH SEVERE ACUTE MALNUTRITION.

Point-of-care ultrasound (POCUS) to diagnose tuberculosis (TB) was assessed in 131 children under 5 years old hospitalized with severe acute malnutrition. Of these, 23% had confirmed or unconfirmed TB and 5% were HIV-infected. There were no POCUS findings associated with TB diagnosis. POCUS visualization quality was satisfactory for 65% and examination acceptability was "good" for 52%.

Optimizing dosing of the cycloserine pro-drug terizidone in children with rifampicin-resistant tuberculosis.

There are no pharmacokinetic data in children on terizidone, a pro-drug of cycloserine and a World Health Organization (WHO)-recommended group B drug for rifampicin-resistant tuberculosis (RR-TB) treatment. We collected pharmacokinetic data in children <15 years routinely receiving 15-20 mg/kg of daily terizidone for RR-TB treatment. We developed a population pharmacokinetic model of cycloserine assuming a 2-to-1 molecular ratio between terizidone and cycloserine. We included 107 children with median (interquartile range) age and weight of 3.33 (1.55, 5.07) years and 13.0 (10.1, 17.0) kg, respectively. The pharmacokinetics of cycloserine was described with a one-compartment model with first-order elimination and parallel transit compartment absorption. Allometric scaling using fat-free mass best accounted for the effect of body size, and clearance displayed maturation with age. The clearance in a typical 13 kg child was estimated at 0.474 L/h. The mean absorption transit time when capsules were opened and administered as powder was significantly faster compared to when capsules were swallowed whole (10.1 vs 72.6 min) but with no effect on bioavailability. Lower bioavailability (-16%) was observed in children with weight-for-age z-score below -2. Compared to adults given 500 mg daily terizidone, 2022 WHO-recommended pediatric doses result in lower exposures in weight bands 3-10 kg and 36-46 kg. We developed a population pharmacokinetic model in children for cycloserine dosed as terizidone and characterized the effects of body size, age, formulation manipulation, and underweight-for-age. With current terizidone dosing, pediatric cycloserine exposures are lower than adult values for several weight groups. New optimized dosing is suggested for prospective evaluation.

Pharmacokinetics and optimized dosing of dispersible and non-dispersible levofloxacin formulations in young children.

BACKGROUND: Levofloxacin is used for treatment and prevention of rifampicin-resistant (RR)-TB in children. Recent data showed higher exposures with 100 mg dispersible compared with non-dispersible tablet formulations with potentially important dosing implications in children. We aimed to verify and better characterize this finding. METHODS: We conducted a crossover pharmacokinetic trial in children aged ≤5 years receiving levofloxacin RR-TB preventive therapy. Pharmacokinetic sampling was done after 15-20 mg/kg doses of levofloxacin with 100 mg dispersible and crushed 250 mg non-dispersible levofloxacin formulations. A population pharmacokinetic model was developed. RESULTS: Twenty-five children were included, median (IQR) weight and age 12.2 (10.7-15.0) kg and 2.56 (1.58-4.03) years, respectively. A two-compartment model with first-order elimination and transit compartment absorption best described levofloxacin pharmacokinetics. Allometric scaling adjusted for body size, and maturation of clearance with age was characterized. Typical clearance in a 12 kg child was estimated at 4.17 L/h. Non-dispersible tablets had 21.5% reduced bioavailability compared with the dispersible formulation, with no significant differences in other absorption parameters.Dosing simulations showed that current recommended dosing for both formulations result in median exposures below adult-equivalent exposures at a 750 mg daily dose, mainly in children >6 months. Higher levofloxacin doses of 16-30 mg/kg for dispersible and 20-38 mg/kg for crushed non-dispersible tablets may be required in children >6 months. CONCLUSIONS: The dispersible paediatric levofloxacin formulation has improved bioavailability compared with the crushed non-dispersible adult formulation, but exposures remain below those in adults. We propose optimized age- and weight-based dosing for levofloxacin, which require further evaluation.

QT Interval Prolongation with One or More QT-Prolonging Agents Used as Part of a Multidrug Regimen for Rifampicin-Resistant Tuberculosis Treatment: Findings from Two Pediatric Studies.

Rifampicin-resistant tuberculosis (RR-TB) involves treatment with many drugs that can prolong the QT interval; this risk may increase when multiple QT-prolonging drugs are used together. We assessed QT interval prolongation in children with RR-TB receiving one or more QT-prolonging drugs. Data were obtained from two prospective observational studies in Cape Town, South Africa. Electrocardiograms were performed before and after drug administration of clofazimine (CFZ), levofloxacin (LFX), moxifloxacin (MFX), bedaquiline (BDQ), and delamanid. The change in Fridericia-corrected QT (QTcF) was modeled. Drug and other covariate effects were quantified. A total of 88 children with a median (2.5th-to-97.5th range) age of 3.9 (0.5 to 15.7) years were included, of whom 55 (62.5%) were under 5 years of age. A QTcF interval of >450 ms was observed in 7 patient-visits: regimens were CFZ+MFX (n = 3), CFZ+BDQ+LFX (n = 2), CFZ alone (n = 1), and MFX alone (n = 1). There were no events with a QTcF interval of >500 ms. In a multivariate analysis, CFZ+MFX was associated with a 13.0-ms increase in change in QTcF (P < 0.001) and in maximum QTcF (P = 0.0166) compared to those when other MFX- or LFX-based regimens were used. In conclusion, we found a low risk of QTcF interval prolongation in children with RR-TB who received at least one QT-prolonging drug. Greater increases in maximum QTcF and ΔQTcF were observed when MFX and CFZ were used together. Future studies characterizing exposure-QTcF responses in children will be helpful to ensure safety with higher doses if required for effective treatment of RR-TB.

Relative bioavailability of delamanid 50 mg tablets dispersed in water in healthy adult volunteers.

AIM: Delamanid is a novel drug for the treatment of drug-resistant tuberculosis, manufactured as 50-mg solid and 25-mg dispersible tablets. We evaluated the effects of dispersing the 50-mg tablet, focusing on the relative bioavailability. METHODS: Delamanid, 50-mg tablets administered dispersed vs swallowed whole, was investigated in a phase I, four-period, crossover study. Two of three dose strengths of delamanid (25, 50 or 100 mg) were given to healthy adult participants, in both whole and dispersed forms, with a 7-day washout period. Blood samples were collected over 168 h after each dose. Delamanid and its metabolite DM-6705 were analysed with a validated liquid chromatography tandem mass spectrometry assay. The pharmacokinetics of both analytes were analysed using nonlinear mixed-effect modelling. Palatability and acceptability were determined using a standardized questionnaire. RESULTS: Twenty-four participants completed the study. The bioavailability of dispersed tablets was estimated to be 107% of whole tablets, with a 90% confidence interval of 99.7-114%, fulfilling bioequivalence criteria. The two formulations were not significantly different regarding either bioavailability or its variability. Bioavailability increased at lower doses, by 34% (26-42%) at 50 mg and by 74% (64-86%) at 25 mg, relative to 100 mg. The majority of participants (93%) found the dispersed formulation acceptable in palatability across all delamanid doses. CONCLUSIONS: Dispersed 50-mg delamanid tablets have similar bioavailability to tablets swallowed whole in adult volunteers. This can be an option for children and other patients who cannot swallow whole tablets, improving access to treatment.

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.

Tuberculosis in Children Living With HIV: Ongoing Progress and Challenges.

There has been much recent progress on control of the tuberculosis (TB) and human immunodeficiency virus (HIV) epidemics globally. However, advances in children have lagged behind, and TB-HIV coinfection continues to be a major driver of pediatric mortality in many settings. This review highlights recent research findings in the areas of prevention, diagnosis, and treatment of HIV-associated childhood TB. Key areas for future research are defined. Current prevention efforts such as vaccination, TB symptom screening, and TB preventive treatment are demonstrated as beneficial but need to be optimized for children living with HIV (CLHIV). Diagnosis of HIV-associated TB in children remains a major challenge, depending heavily on clinicians' ability to judge an array of signs, symptoms, and imaging findings, but there are a growing number of promising diagnostic tools with improved accuracy and feasibility. Treatment of TB-HIV coinfection has also seen recent progress with more evidence demonstrating the safety and effectiveness of shorter regimens for treatment of TB infection and disease and improved understanding of interactions between antiretrovirals and TB medications. However, several evidence gaps on drug-drug interactions persist, especially for young children and those with drug-resistant TB. Accelerated efforts are needed in these areas to build upon current progress and reduce the burden of TB on CLHIV.

New Drugs and Regimens for Tuberculosis Disease Treatment in Children and Adolescents.

After almost 30 years of relative stagnation, research over the past decade has led to remarkable advances in the treatment of both drug-susceptible (DS) and drug-resistant (DR) tuberculosis (TB) disease in children and adolescents. Compared with the previous standard therapy of at least 6 months, 2 new regimens lasting for only 4 months for the treatment of DS-TB have been studied and are recommended by the World Health Organization (WHO), along with a shortened 6-month regimen for treatment of DS-TB meningitis. In addition, the 18- to 24-month regimens previously used for DR-TB that included painful injectable drugs with high rates of adverse effects have been replaced with shorter, safer all-oral regimens. Advances that have improved treatment include development of new TB drugs (bedaquiline, delamanid, pretomanid), reapplication of older TB drugs (rifampicin and rifapentine), and repurposing of other drugs (clofazimine and linezolid). The development of child-friendly formulations for many of these drugs has further enhanced the ability to safely and effectively treat DS- and DR-TB in children and adolescents. The characteristics and use of these drugs, regimens, and formulations are reviewed.

Hepatocellular Injury in Children Treated for Rifampicin-resistant Tuberculosis: Incidence, Etiology and Outcome.

BACKGROUND: Hepatocellular injury has been reported commonly in adults on rifampicin-resistant and multidrug-resistant tuberculosis (RR/MDR-TB) treatment. However, there are limited data in children. METHODS: Two pharmacokinetic studies of children (0-17 years) routinely treated for RR/MDR-TB were conducted in Cape Town, South Africa between October 2011 and February 2020. Hepatocellular injury adverse events (AEs; defined as elevated alanine aminotransferase [ALT]) were documented serially. Data were analyzed to determine the incidence, etiology, risk factors, management and outcome of ALT elevation. RESULTS: A total of 217 children, median age 3.6 years (interquartile range, 1.7-7.1 years) at enrollment were included. The median follow-up time was 14.0 months (interquartile range, 9.8-17.2 months). Fifty-five (25.3%) patients developed an ALT AE. Of these, 43 of 55 (78%) patients had 54 ALT AEs attributed to their RR/MDR-TB treatment. The incidence rate of ALT AEs related to RR-TB treatment was 22.4 per 100 person-years. Positive HIV status and having an elevated ALT at enrollment were associated with time to ALT AE attributed to RR/MDR-TB treatment, with P values 0.0427 and P < 0.0001, respectively. Hepatitis A IgM was positive in 11 of 14 (78.6%) severe (grade ≥3) cases of ALT AEs. In 8 of 14 (57%) severe ALT AEs, hepatotoxic drugs were stopped or temporarily interrupted. None had a fatal or unresolved outcome. CONCLUSIONS: Hepatocellular injury in children on RR/MDR-TB treatment is common, although usually mild; having elevated ALT early in treatment and HIV-positive status are possible risk factors. Hepatitis A was a common etiology of severe ALT AE in children treated for RR/MDR-TB.

Practical and psychosocial challenges faced by caregivers influence the acceptability of multidrug-resistant tuberculosis preventive therapy for young children.

Drug-resistant (DR) strains of Mycobacterium tuberculosis (M. tb) are increasingly recognised as a threat to global tuberculosis (TB) control efforts. Identifying people with DR-TB exposure/ infection and providing TB preventive therapy (TPT) is a public health priority. TB guidelines advise the evaluation of household contacts of newly diagnosed TB cases, with the provision of TPT to vulnerable populations, including young children (<5 years). Many children become infected with TB through exposure in their household. Levofloxacin is under evaluation as TPT in children exposed to M. tb strains with resistance to rifampicin and isoniazid (multidrug-resistant TB; MDR-TB). Prior to opening a phase 3 prevention trial in children <5 years exposed to MDR-TB, the pharmacokinetics and safety of a novel formulation of levofloxacin given daily was evaluated as part of a lead-in study. We conducted an exploratory qualitative study of 10 caregivers' experiences of administering this formulation. We explored how the acceptability of levofloxacin as TPT is shaped by the broader impacts of MDR-TB on the overall psychological, social, and financial wellbeing of caregivers, many of whom also had experienced MDR-TB. Caregivers reported that the novel levofloxacin formulation was acceptable. However, caregivers described significant psychosocial challenges in the process of incorporating TPT administration to their children into their daily lives, including financial instability, withdrawal of social support and stigma. When caregivers themselves were sick, these challenges became even more acute. Although new child-friendly formulations can ameliorate some of the pragmatic challenges related to TPT preparation and administration, the overall psychosocial burden on caregivers responsible for administering TPT remains a major determinant of effective MDR-TB prevention in children.

Pharmacokinetics and Dose Optimization Strategies of Para-Aminosalicylic Acid in Children with Rifampicin-Resistant Tuberculosis.

Treatment options for children with Rifampicin-resistant tuberculosis (RR-TB) remain limited, and para-aminosalicylic acid (PAS) is still a relevant component of treatment regimens. Prevention of resistance to companion drugs by PAS is dose related, and at higher concentrations, PAS may exhibit significant bactericidal activity in addition to its bacteriostatic properties. The optimal dosing of PAS in children is uncertain, specifically for delayed-release granule preparations, which are the most used. A population pharmacokinetic model was developed describing PAS pharmacokinetics in children receiving routine RR-TB treatment. Model-based simulations evaluated current World Health Organization (WHO) weight-band doses against the adult pharmacokinetic target of 50 to 100 mg/liter for peak concentrations. Of 27 children included, the median (range) age and weight were 3.87 (0.58 to 13.7) years and 13.3 (7.15 to 30.5) kg, respectively; 4 (14.8%) were HIV positive. PAS followed one-compartment kinetics with first-order elimination and transit compartment absorption. The typical clearance in a 13-kg child was 9.79 liters/h. Increased PAS clearance was observed in both pharmacokinetic profiles from the only patient receiving efavirenz. No effect of renal function, sex, ethnicity, nutritional status, HIV status, antiretrovirals (lamivudine, abacavir, and lopinavir-ritonavir), or RR-TB drugs was detected. In simulations, target concentrations were achieved only using the higher WHO dose range of 300 mg/kg once daily. A transit compartment adequately describes absorption for the slow-release PAS formulation. Children should be dosed at the higher range of current WHO-recommended PAS doses and in a once-daily dose to optimize treatment.

Treatment of Rifampicin-Resistant Tuberculosis Disease and Infection in Children: Key Updates, Challenges and Opportunities.

Children affected by rifampicin-resistant tuberculosis (RR-TB; TB resistant to at least rifampicin) are a neglected group. Each year an estimated 25,000-30,000 children develop RR-TB disease globally. Improving case detection and treatment initiation is a priority since RR-TB disease is underdiagnosed and undertreated. Untreated paediatric TB has particularly high morbidity and mortality. However, children receiving TB treatment, including for RR-TB, respond well. RR-TB treatment remains a challenge for children, their caregivers and TB programmes, requiring treatment regimens of up to 18 months in duration, often associated with severe and long-term adverse effects. Shorter, safer, effective child-friendly regimens for RR-TB are needed. Preventing progression to disease following Mycobacterium tuberculosis infection is another key component of TB control. The last few years have seen exciting advances. In this article, we highlight key elements of paediatric RR-TB case detection and recent updates, ongoing challenges and forthcoming advances in the treatment of RR-TB disease and infection in children and adolescents. The global TB community must continue to advocate for more and faster research in children on novel and repurposed TB drugs and regimens and increase investments in scaling-up effective approaches, to ensure an equitable response that prioritises the needs of this vulnerable population.

Drug concentration at the site of disease in children with pulmonary tuberculosis.

BACKGROUND: Current TB treatment for children is not optimized to provide adequate drug levels in TB lesions. Dose optimization of first-line antituberculosis drugs to increase exposure at the site of disease could facilitate more optimal treatment and future treatment-shortening strategies across the disease spectrum in children with pulmonary TB. OBJECTIVES: To determine the concentrations of first-line antituberculosis drugs at the site of disease in children with intrathoracic TB. METHODS: We quantified drug concentrations in tissue samples from 13 children, median age 8.6 months, with complicated forms of pulmonary TB requiring bronchoscopy or transthoracic surgical lymph node decompression in a tertiary hospital in Cape Town, South Africa. Pharmacokinetic models were used to describe drug penetration characteristics and to simulate concentration profiles for bronchoalveolar lavage, homogenized lymph nodes, and cellular and necrotic lymph node lesions. RESULTS: Isoniazid, rifampicin and pyrazinamide showed lower penetration in most lymph node areas compared with plasma, while ethambutol accumulated in tissue. None of the drugs studied was able to reach target concentration in necrotic lesions. CONCLUSIONS: Despite similar penetration characteristics compared with adults, low plasma exposures in children led to low site of disease exposures for all drugs except for isoniazid.