The U.S. Food and Drug Administration on Wednesday said it will temporarily allow certain manufacturers to sell blood pressure medications containing specified levels of a probable cancer-causing impurity in order to maintain adequate supplies of the drug.

The agency said losartan medicines remaining on the market that contain the impurity N-Nitroso-N-methyl-4-aminobutyric acid (NMBA) above the acceptable limit of 0.96 parts per million (ppm) and below 9.82 ppm will be allowed until the impurity can be eliminated.

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Since last summer, the FDA has been conducting a major investigation to address the presence of certain impurities in a class of drugs called angiotensin II receptor blockers (ARBs), including losartan.

Some generic versions of other ARBs such as valsartan and irbesartan have also been recalled, and the agency in January warned of the possibility of additional shortages of the widely used drugs in the United States.

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Last week, the FDA approved a new generic version of valsartan to ease the shortages triggered by several manufacturers recalling the drug over possible cancer risk.

The FDA on Wednesday said it expects companies to be able to manufacture losartan without the probable carcinogen and replenish supplies in the United States in about six months.

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Agency scientists have found that exposure to the NMBA impurity within specified levels present no meaningful difference in cancer risk over a six-month time period when compared to a lifetime of exposure, the FDA said in an update on its website.

Global authorities have clamped down on sales of some of these hypertension medicines, leading to drugmakers such as Teva Pharmaceutical Industries Ltd and Mylan NV pulling batches of the drugs that have been found to contain probable carcinogens.