Online pharmacy Valisure has discovered another cancer-causing chemical in blood-pressure pills made by companies including Novartis, according to a petition to the U.S. Food and Drug Administration.

The filing to the FDA on Thursday involves dimethylformamide, or DMF, a solvent detected in the heart drug valsartan, according to Valisure. The New Haven, Connecticut-based pharmacy operation requested that the FDA lower how much DMF is allowed in medications and to recall the valsartan determined to hold high levels of DMF.

Multiple versions of generic valsartan have been recalled since last year, when the chemical N-Nitrosodimethylamine, or NDMA, was found in a Chinese-made version of valsartan, as drug that for decades has been used to treat hypertension.

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The FDA in March said the impurities found in the recalled medications may have been the result of chemical reactions that occur in the drugmaking process or from the reuse of materials, such as solvents.

The FDA will review Valisure's findings, an agency spokesperson told CBS MoneyWatch. Consumers should continue to take their blood-pressure medication regardless of whether it's been recalled until they can consult with their physician, according to the regulatory agency.

"The risk associated with abruptly discontinuing the use of these important medicines far outweighs the low risk that our scientists estimate to be associated with continuing the medicine until the patient's doctor or pharmacist provides a safe replacement or a different treatment option," the FDA spokesperson stated.

The World Health Organization classified DMF as a probable carcinogen last year.

The FDA does not routinely test pharmaceuticals, counting on manufacturers to make sure their products are safe and effective.

Novartis, which makes Diovan, a brand-name version of valsartan, said it generally does not use DMF in making its medications, and information from its suppliers indicated that they do not, either.

That said, "Novartis cannot currently fully exclude the possibility that traces of DMF (within applicable limits) may have been present in materials of other drug substances suppliers," a spokesperson for the drugmaker told CBS MoneyWatch.