Nearly 6,000 people with latent (inactive) tuberculosis will be enrolled in five cities across Canada as well as in the West African countries of Benin and Guinee, in Brazil, South Korea, Australia and Saudi Arabia.According to the article rifampin is less harmful to the liver (less than 1% compared to 3.8% of people taking isoniazid) but interacts badly with a large number of other medications, including beta blockers, opiod pain killers and birth control pills.
Half will receive the current regimen used to try to cure latent TB infection, once-a-day treatment with the drug isoniazid (called INH for short) for nine months. The other half will receive the drug rifampin (also known as rifampicin) for four months.
Both groups will be followed for 28 months from recruitment to see how many go on to develop active TB - which should tell if rifampin is as efficacious as isoniazid. Menzies says it will take about seven years to arrive at the answer of the nearly $5-million study.
Both Dr. Michael Gardam, director of the tuberculosis clinic at Toronto Western Hospital and Dr. Dick Menzies, McGill University' agree that gaining patient confidence is critical;
Only a small percentage of people who have latent TB - somewhere between five to 10 per cent - will go on to develop active disease. Given that fact, and the fact that people who have latent TB don't feel sick, telling people they should take a drug that might destroy their liver can be a "a hard sell," Gardam says.The crux of the problem is that they are still using a 100 year old test to diagnose latent TB, a test with well known, recorded and proven record of misdiagnosis, something that Dick Menzies (along with Drs Madhukar Pai and George Comstock) has already stated;
Menzies agrees: "Very hard to sell to patients - and even to doctors. A lot of doctors won't give this stuff."
The tuberculin skin test is 1 of the few tests that has been in use for nearly 100 years in clinical medicine (1). Therefore, it is not surprising that the test has important limitations. The tuberculin skin test uses a relatively crude mix of antigens from Mycobacterium tuberculosis. As a result, falsepositive reactions can occur because of previous bacille Calmette–Guérin (BCG) vaccination or sensitization to nontuberculous mycobacteria. False-negative results on tuberculin skin tests can occur because of severe illness, including active tuberculosis (TB), or immune suppression, often due to HIV infection. Initial testing can affect results of subsequent tests because of anamnestic recall of immunity (the booster effect). Errors in administration or reading can lead to incorrect results. The variability of the tuberculin skin test can be minimal with well-trained personnel using meticulous techniques (2–8), although such personnel are not always available. Interpretation of test results requires a thorough understanding of the test.
Greater accuracy and predictability can be obtained by using a laboratory based blood test, such as QuantiFERON;
Results suggest QFT screening determines more accurately than TST the presence of LTBI with at least equivalent sensitivity for predicting progression to TB. The high rate of progression to active TB of those QFT positive (14.6%), far greater than the 2.3% found for those TST positive, has significant health and economic implications for enhanced TB control.Before Canada embarks on such a study it is important that they clarify just how they will diagnose LTBI; if they are to use only the TST there exists a potential for distortion through misdiagnosis which could compromise confidence in any outcome.
