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WASHINGTON -- All ranitidine products should be pulled from shelves immediately, , including brand-name Zantac as well as generic versions of the prescription and over-the-counter antacid.

Notably, this was not because of direct evidence of N-Nitrosodimethylamine (NDMA), a probable human carcinogen, being present in particularly high concentrations in the drug itself.

"We didn't observe unacceptable levels of NDMA in many of the samples that we tested. However, since we don't know how or for how long the product might have been stored, we decided that it should not be available to consumers and patients unless its quality can be assured," Janet Woodcock, MD, director of the FDA's Center for Drug Evaluation and Research, said in a statement.

"The agency has determined that the impurity in some ranitidine products increases over time and when stored at higher than room temperatures may result in consumer exposure to unacceptable levels of this impurity," according to the FDA announcement.

Reports of NDMA impurities in ranitidine began in the summer of 2019, following similar discoveries in valsartan and other generic angiotensin receptor blockers, where nitrosamine impurities were found to be created during faulty manufacturing of active pharmaceutical ingredients.

"Ranitidine stands out as the NDMA contamination does not seem to be formed during manufacturing, but appears over time in storage. This is a "new source of NDMA," Woodcock said during a press briefing."

How much of the storage problem can be attributed to drug packaging or formulation is unknown, she said.

Various ranitidine products have already been subject to voluntary recalls in the past few months. The present "market withdrawal" by the FDA is a different action, Woodcock clarified.

"This is not a recall because technically the products are okay. Only when they’re subject to this heat stress do they manifest higher levels [of NDMA]," she said. "When they come off the manufacturing line, they don't have NDMA in them."

Now, the FDA is sending letters to all manufacturers of ranitidine requesting they withdraw their products from the market. The agency is also advising consumers to stop buying and taking over-the-counter ranitidine. Those who wish to continue treatment to relieve gastroesophageal reflux and for gastric and intestinal ulcer prevention should consider using other approved products, the FDA said.

Manufacturers are welcome to reformulate ranitidine products that remain stable over time, Woodcock said.

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