BEIJING - China's food and drug watchdog has told the country's pharmaceutical firms to carefully scrutinize their material sources to prevent substandard ingredients being used in medicine.

The State Food and Drug Administration (SFDA) has asked drug enterprises to audit their suppliers to ensure the quality of ingredients and medicine products, according to a report in the Sunday edition of the People's Daily, the flagship newspaper of the Communist Party of China.

In a Friday statement, the administration announced an investigation into the truth of a media exposure alleging that certain pharmaceutical firms have been manufacturing an antibiotic intermediate using "gutter oil."

Gutter oil, referring to reprocessed oil made from kitchen waste dredged from gutters behind restaurants, has been in the center of a spate of food safety scandals in China, after it was found to be illegally reused by restaurants or bottled for sale.

The drug watchdog has organized experts to evaluate the safety risk of the involved cephalosporin antibiotics, for one of its materials is made by using soya-bean oil which could have been blended with the waste cooking oil, the SFDA statement said.