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test the safety and efficacy of this new formulation in young children

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Bringing antiretroviral drugs to children

The CHAPAS trials have ensured that many more children with HIV have benefited
from life-saving antiretrovirals.

The challenge

Drug-resistant tuberculosis presents a challenge to global control of tuberculosis. Globally, 45% of the 480,000 cases of multidrug-resistant tuberculosis (MDR-TB) is detected, and at most 70% of these patients receive appropriate drug therapy.

Tanzania has adopted rapid molecular methods for dual detection of Mycobacterium tuberculosis complex (MTBC) and susceptibility to either rifampicin alone or with isoniazid and second-line injectable and fluoroquinolones using Xpert MTB/Rif assay, genotype MTBDRplus and MTBDRsl.

These assays only target predetermined regions of the genome known to predict phenotypic resistance to anti-TB drugs. This leads to the isolate being incorrectly called susceptible. Thus, undetected patients are likely to fail treatment but also spread resistance organisms. A recent retrospective study in Tanzania has found a diversity of mutations, including rrs and gyrB, which code for second-line drugs, suggesting ongoing transmission of MDR-TB strains rather than de novo evolution or importation of drug resistance strains.

Dr Katale hypothesises that whole-genome sequencing of MDR-TB strains will improve the diagnosis and treatment of TB in Tanzania while providing precise strain discrimination. The study is designed as a case-control study in which sputum samples will be collected from TB patients attending health services at the TB-dedicated Kibong’oto Hospital, in northern Tanzania.

Cases will be defined as MDR-TB patients when confirmed by culture and drug-susceptibility testing (DST) as having resistance to at least rifampicin and isoniazid. Controls will be patients who are sensitive to rifampicin and isoniazid.

Samples will be processed using the modified Petroff’s method. Culture and identification of MTBC colonies will be performed according to local and CLSI standard operating procedures. Phenotypic DST of the MTBC isolates will be performed using Mycobacteria Growth Indicator Tube DST. Genomic DNA will be extracted using a modified protocol based on Restriction Fragment Length Polymorphism and sequenced using MiseqTM. The whole-genome sequencing and bioinformatic analysis will be performed to determine mutations that predict phenotypic resistance to anti-TB drugs. Immunological and haematological assays will be performed to associate between types of drug-resistance genes, alone or in combination, and TB progression/severity. Patient’s clinical information and outcomes will be obtained and compared to phenotypic and genetic data.

The project

The later CHAPAS-3 trial compared the efficacy and safety of three fixed-dose combinations including two without stavudine (found to have some long-term side effects in adults, leading to a recommendation that its use be discontinued in children). The trial the first of its kind in Africa studied nearly 500 children at four sites in two African countries.

This study will provide insights into the role of whole-genome sequencing in the clinical management of patients and the role of drug-resistance genes in the progression and severity of TB infections.

ratios forfixed-dose combinations and on appropriatedosage according to weight. 

The CHAPAS-3 trial confirmed the effectiveness of fixed-dose combinations, providing further impetus to the rollout of antiretrovirals to children. Its evidence on abacavir informed the WHO recommendation of abacavir-containing combinations for first-line therapy in children. Trial data have also been used to support applications for regulatory approval for new scored efavirenz tablets.

Impact