Viona Pharmaceuticals Inc is recalling 21,240 bottles of metformin hydrochloride extended-release tablets, USP 750 mg, on account of "CGMP Deviations: FDA analysis detected n-nitrosodimethylamine (NDMA) levels in excess of the acceptable daily intake limit", the report by the US health regulator said. 

The voluntary ongoing nationwide recall in the US is a class-II recall, it added. 

As per USFDA, a class-II recall is initiated in a situation in which use of, or exposure to, a violative product may cause temporary or medically reversible adverse health consequences or where the probability of serious adverse health consequences is remote. 

NDMA is classified as a probable human carcinogen based on results from laboratory tests. It is a known environmental contaminant and found in water and foods, including meats, dairy products and vegetables.