TB drug resistance — New tests set to improve treatment efficacy among patients

Tuberculosis can be resistant to treatment with several different drugs. Tests that identify which drugs someone’s TB is resistant to are critical to ensuring that people are not treated with drugs that don’t work for them, especially given the significant side effects associated with some of the drugs. Elri Voigt assesses the state of play in testing for TB drug resistance and the promise of exciting new technologies, such as whole genome sequencing.
Some strains of the tuberculosis (TB) bacterium have mutated to become resistant to some of the drugs commonly used to treat TB. Accordingly, one of the first questions to ask when someone has TB is which drugs will be effective in fighting that person’s TB. Unfortunately, quick answers to this question are not always available. As a consequence, people are at times treated with drugs that won’t work for their particular strain of TB. What’s worse, these drugs often have significant side effects.
As a result, the race is on to develop quick and affordable resistance tests for all commonly used TB drugs.
But first, some alphabet soup to set the scene. Drug-sensitive TB (DS-TB) is TB that is not resistant to any of the four standard drugs used to treat TB. RR-TB is TB that is resistant to rifampicin (one of those standard four drugs). MDR-TB (multi-drug resistant) is resistant to both rifampicin and isoniazid (isoniazid is also one of the standard four). People with RR or MDR-TB are treated with anything from three to seven drugs, mostly different from those first four. Pre-XDR-TB (extensively drug-resistant) is MDR-TB that is also resistant to a class of drugs called fluoroquinolones (most common examples are moxifloxacin and levofloxacin). XDR-TB is pre-XDR-TB that is also resistant to one of an additional list of drugs (the most notable on this list being bedaquiline).
Why better testing for drug-resistant TB is needed
Many people undergo a long diagnostic process and might not be properly diagnosed for TB, let alone DR-TB, explains David Branigan, TB Project Officer at the New York-based Treatment Action Group (TAG). As a result, he says, some TB patients may be undergoing treatment failure due to being on the wrong treatment regimen.
“That’s not appropriate. It’s not okay to treat people like that. There needs to be a better standard of care that’s implemented,” he says.
Part of the solution is to make better use of existing resistance tests, but since quick tests for resistance ...