(Bloomberg) -- Two life-saving tuberculosis drugs were found to contain elevated levels of chemicals that may cause cancer, according to the Food and Drug Administration, but the treatments will be allowed to remain on the market out of worry that supplies could run short.
The drugs rifampin and rifapentine contain nitrosamine impurities, the FDA said in a statement Wednesday. A similar chemical contamination led to recalls in the past two years for millions of blood-pressure pills, as well as brand and generic forms of the heartburn medicine Zantac and a popular diabetes therapy. Some nitrosamine compounds are considered possible or probable human carcinogens.
The FDA is permitting the tuberculosis drugs to be used by patients as the companies that make them work to eliminate the contamination. The agency said tuberculosis patients should continue taking their medication and talk to their doctor about any concerns. The FDA is investigating the origin of the impurities, according to the statement.
Rifapentine is sold in the U.S. under the brand name Priftin by Sanofi; there are no approved or marketed generic drug products for rifapentine, FDA spokesman Jeremy Kahn said in an email. He said there aren't any rifampin or rifapentine recalls at this time.
While the findings of contamination echo previous episodes, the precise compounds detected are different. Rifampin and rifapentine were discoverd to contain chemical agents called 1-methyl-4-nitrosopiperazine, or MNP, and 1-cyclopentyl-4-nitrosopiperazine, or CPNP.
Blood-pressure pills including valsartan and losartan, as well as Zantac and the diabetes drug metformin, largely contained a nitrosamine impurity called N-Nitrosodimethylamine, or NDMA.
Manufacturers have identified MNP in both generic and brand-name rifampin, Kahn said.
Some drugmakers have already taken action after finding impurities in the therapies. Mylan NV recalled more than 19,000 vials of rifampin in October for “elevated unknown impurity results,” according to the FDA website. Rifampin is also used to treat other serious infections.
Mylan didn't immediately respond to a request for comment.
Tuberculosis is a potentially deadly disease that typically affects the lungs. About 9,000 tuberculosis cases were reported in the U.S. in 2018, according to the Centers for Disease Control and Prevention.
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