Rifapentine pharmacokinetics in adolescents

High-dose rifapentine with or without moxifloxacin for shortening treatment of pulmonary tuberculosis: Study protocol for TBTC study 31/ACTG A5349 phase 3 clinical trial

INTRODUCTION

Phase 2 clinical trials of tuberculosis treatment have shown that once-daily regimens in which rifampin is replaced by high dose rifapentine have potent antimicrobial activity that may be sufficient to shorten overall treatment duration. Herein we describe the design of an ongoing phase 3 clinical trial testing the hypothesis that once-daily regimens containing high dose rifapentine in combination with other anti-tuberculosis drugs administered for four months can achieve cure rates not worse than the conventional six-month treatment regimen.

METHODS/DESIGN

S31/A5349 is a multicenter randomized controlled phase 3 non-inferiority trial that compares two four-month regimens with the standard six-month regimen for treating drug-susceptible pulmonary tuberculosis in HIV-negative and HIV-positive patients. Both of the four-month regimens contain high-dose rifapentine instead of rifampin, with ethambutol replaced by moxifloxacin in one regimen. All drugs are administered seven days per week, and under direct observation at least five days per week. The primary outcome is tuberculosis disease-free survival at twelve months after study treatment assignment. A total of 2500 participants will be randomized; this gives 90% power to show non-inferiority with a 6.6% margin of non-inferiority.

DISCUSSION

This phase 3 trial formally tests the hypothesis that augmentation of rifamycin exposures can shorten tuberculosis treatment to four months. Trial design and standardized implementation optimize the likelihood of obtaining valid results. Results of this trial may have important implications for clinical management of tuberculosis at both individual and programmatic levels.

TRIAL REGISTRATION

NCT02410772. Registered 8 April 2015,https://www.clinicaltrials.gov/ct2/show/NCT02410772?term=02410772&rank=1.

Rifapentine Pharmacokinetics and Tolerability in Children and Adults Treated Once Weekly With Rifapentine and Isoniazid for Latent Tuberculosis Infection

BACKGROUND

In a phase 3, randomized clinical trial (PREVENT TB) of 8053 people with latent tuberculosis infection, 12 once-weekly doses of rifapentine and isoniazid had good efficacy and tolerability. Children received higher rifapentine milligram per kilogram doses than adults. In the present pharmacokinetic study (a component of the PREVENT TB trial), rifapentine exposure was compared between children and adults.

METHODS

Rifapentine doses in children ranged from 300 to 900 mg, and adults received 900 mg. Children who could not swallow tablets received crushed tablets. Sparse pharmacokinetic sampling was performed with 1 rifapentine concentration at 24 hours after drug administration (C24). Rifapentine area under concentration-time curve (AUC) was estimated from a nonlinear, mixed effects regression model (NLME).

RESULTS

There were 80 children (age: median, 4.5 years; range, 2-11 years) and 77 adults (age: median, 40 years; all ≥18 years) in the study. The geometric mean rifapentine milligram per kilogram dose was greater in children than in adults (children, 23 mg/kg; adults, 11 mg/kg). Rifapentine geometric mean AUC and C24 were 1.3-fold greater in children (all children combined) than in adults. Children who swallowed whole tablets had 1.3-fold higher geometric mean AUC than children who received crushed tablets, and children who swallowed whole tablets had a 1.6-fold higher geometric mean AUC than adults. The higher rifapentine doses in children were well tolerated. To obtain rifapentine exposures comparable in children to adults, dosing algorithms modeled by NLME were developed.

CONCLUSIONS

A 2-fold greater rifapentine dose for all children resulted in a 1.3-fold higher AUC compared to adults administered a standard dose. Use of higher weight-adjusted rifapentine doses for young children are warranted to achieve systemic exposures that are associated with successful treatment of latent tuberculosis infection in adults.

Human immunodeficiency virus and tuberculosis coinfection in children: challenges in diagnosis and treatment

The burden of childhood tuberculosis (TB) is influenced by the human immunodeficiency virus (HIV) epidemic and this dangerous synergy affects various aspects of both diseases; from pathogenesis and the epidemiologic profile to clinical presentation, diagnosis, treatment, and prevention. HIV-infected infants and children are at increased risk of developing severe forms of TB. The TB diagnosis is complicated by diminished sensitivity and specificity of clinical features and diagnostic tools like the tuberculin skin test and chest x-ray. Although alternative ways of pulmonary sampling and the development of interferon-γ assays have shown to lead to some improvement of TB diagnosis in HIV-infected children, new diagnostic tools are urgently needed. Coadministration of anti-TB treatment and antiretroviral drugs induces severe complications, and this highlights the need to define optimal treatment regimens. Practical implementation of these regimens in TB control programs should be combined with isoniazid preventive therapy in TB-exposed HIV-infected children. The risk of severe complications after Bacille Calmette-Guérin vaccination of HIV-infected children emphasizes the need for new nonviable vaccines. This article reviews the current status of pediatric HIV-TB coinfection with specific emphasis on the diagnosis and treatment.

Adolescents in clinical trials

Drug development is a lengthy, costly, and complex process, with clinical trials essential for characterizing dosing, safety, and efficacy in treated populations. After regulatory approval, aggressive marketing ensures that most drugs are used by a broad spectrum of ages, genders, races, and ethnic groups. Unfortunately, not all groups are adequately represented in clinical trials; adolescents are commonly overlooked. This commentary explores how adolescents are considered during drug development, with a special focus on the influence of inherent psychosocial, biological, ethical, and regulatory issues in their recruitment and participation in clinical studies leading to drug licensing.

Pharmacokinetics of rifapentine in children

BACKGROUND

Rifapentine is a rifamycin antibiotic approved for the treatment of pulmonary infections caused by Mycobacterium tuberculosis. Although the pharmacokinetics of rifapentine has been investigated in adolescents and adults, no studies have assessed the pharmacokinetics of this drug in children or infants.

METHODS

Twenty-four children (7.1 +/- 3.3 years; mean +/- 1 SD, 27.9 +/- 11.9 kg) were enrolled in this open label study. Children received a single oral dose (10 to <30 kg body weight received 150 mg; 30 to <60 kg body weight received 300 mg), followed by repeated blood sampling (n = 11) for 32 hours. Rifapentine and 25-desacetyl rifapentine were quantitated by a validated high-pressure liquid chromatography method. Pharmacokinetic parameters were determined using a model-independent approach.

RESULTS

A significant difference in dose-normalized area under the curves (AUC0-n and AUC0-infinity) was observed between children receiving the 150 and 300 mg doses, which was accounted for by differences in age between the dosing arms. In separate analyses, including data from adults, further age-dependence in total body exposure (reflected by AUC) and elimination was observed. Adverse events associated with rifapentine were mild and included gastric distress (n = 1) and vomiting (n = 2).

CONCLUSIONS

Given a comparable weight-normalized dose, rifapentine exposure estimates are lower in children than those reported in adults, suggesting that a larger weight-normalized (ie, mg/kg) dose of rifapentine is needed in children.

In vitro postantibiotic effects of rifapentine, isoniazid, and moxifloxacin against Mycobacterium tuberculosis

Postantibiotic effects (PAEs) of rifapentine, isoniazid, and moxifloxacin against Mycobacterium tuberculosis ATCC 27294 were studied using a radiometric culture system. Rifapentine at 20 mg/liter gave the longest PAE (104 h) among the drugs used alone. The combinations of rifapentine plus isoniazid, rifapentine plus moxifloxacin, and isoniazid plus moxifloxacin gave PAEs of 136.5, 59.0, and 8.3 h, respectively.