Older adults who take isoniazid for inactive tuberculosis (TB) infection may be at increased risk of hepatotoxicity from the medication, a new study suggests.
Canadian researchers found that among all Quebec residents treated for latent TB over six years, 2.6% of those older than 65 were hospitalised for liver damage, compared to 0.2% of those in the same age group who were not treated for latent TB, the authors reported online in the Canadian Medical Association Journal.
The findings, researchers say, suggest that doctors need to carefully weigh the pros and cons of treating latent TB in older individuals.
Quantify isoniazid risk
Liver damage is a known side effect of isoniazid. But until now, no large studies had looked at how often treatment of latent TB causes serious liver problems in the general population.
"The main goal of this study was to quantify the risk," said lead researcher Dr Benjamin A. Smith, of McGill University in Canada. "We were able to get a real-world picture, so we can give meaningful information to patients."
He adds that the findings suggest that with older adults, the risk of latent TB reactivation needs to be carefully weighed against the risk of liver damage from treatment.
The picture can get complex, he noted. Along with the main risk factors for TB reactivation - like chemotherapy and HIV infection - diabetes and advanced kidney disease can also raise the odds of TB reactivation.
"If you have someone who is 20 years old, you're going to be much less concerned about liver damage," Smith continued. "So you're probably going to treat if they have diabetes, or any other risk factor," Smith said. But with someone older than 65, he added, "it gets more complicated."
The findings are based on government health records for Quebec's 7.7 million residents. Between 1998 and 2003, a total of 9,145 residents were treated for latent TB. For each of those patients, Smith and his colleagues matched two controls by age and gender.
Of the total treated cohort, 45 were hospitalised for liver damage - typically for non-infectious hepatitis.
Adults older than 65 accounted for 22 of those 45 hospitalisations.
Older adults treated for latent TB were, not surprisingly, in poorer overall health than the comparison group. But even after adjustment for comorbidities, those treated for latent TB were still six times more likely to be hospitalised for liver damage than untreated older adults.
There was also a slightly higher rate of hospitalisations among 36- to 65-year-olds treated for latent TB, compared with those of the same age who were uninfected. But when other health problems were considered, the treatment itself was not clearly linked to increased risk.
Know the risks
The bottom line, according to Smith, is that patients with latent TB need to understand all the potential risks of treating, or not treating, it. One option could be to treat, and do monthly liver-function tests to detect any signs of damage early, he notes.
An estimated one-third of the world's population carries latent TB. It's most common in Russia, India, China, sub-Saharan Africa and parts of South America. In the US, an estimated 10 million to 15 million people have latent TB. - (Amy Norton/Reuters Health, January 2011)