Novartis AG said it is working with authorities in 23 countries to shore up supplies of hypertension treatment valsartan, once one of the Swiss drugmaker's best sellers, after a recall of medicines containing an ingredient supplied by Zhejiang Huahai Pharmaceutical Co. Ltd.

Zhejiang Huahai, based in China, detected an impurity known as N-nitrosodimethylamine, or NDMA — a substance that could cause cancer — in the valsartan active ingredient that it sells to some manufacturers producing medicines available in the EU.

The recall consists of approximately 2,300 batches of valsartan and valsartan and hydrochlorothiazide film-coated tablets made by Novartis' Sandoz International GmbH unit and distributed in Germany, Norway, Finland, Sweden, Hungary, the Netherlands, Austria, Ireland, Bulgaria, Italy, Spain, Portugal, Belgium, Luxembourg, France, Poland, Croatia, Lithuania, Greece, Canada, Bosnia and Herzegovina, Bahrain and Malta. The countries were notified June 27.

"Further availability of this key medicinal product for patients is a top priority for us," Novartis spokesman Jim Sheldrake said in an emailed statement Aug. 7. "Therefore, we are exploring possible options with the health authorities to facilitate a continuous supply to cover patient needs."

Patients should not stop taking the medication or switch to an alternative product without checking with the doctor who prescribed valsartan to ensure treatment is not disrupted, Sheldrake said.

Novartis noted in their statement that the recall does not affect their brand name products containing valsartan, such as Diovan, CoDiovan, Exforge, Exforge HCT and Entresto. It also does not affect Sandoz products sold in the U.S.

The U.S. Food and Drug Administration expanded its recall of non-Sandoz generic valsartan drugs Aug. 2. The drugs include the same valsartan and valsartan/HCT tables. This is the second update of affected products, following the initial announcement July 13.

The recalled valsartan tablets, as listed on the FDA website, include products from Teva Pharmaceutical Industries Ltd., also labeled as Major Pharmaceuticals Inc. and Actavis, Solco Healthcare, A-S Medication Solutions LLC, Bryant Ranch Prepack Inc., HJ Harkins Co. and Northwind Pharmaceuticals LLC. The recalled valsartan/HCT tablets include products from Teva Pharmaceuticals labeled as Actavis, Solco Healthcare, AvKARE, Remedy Repack, A-S Medication, Proficient Rx and Northwind Pharmaceuticals.

Products not affected by the recall can also be found on the FDA website.