Irregularities have been found in some samples of the drug linked to six deaths in eastern China, the State Food and Drug Administration (SFDA) said Monday in a statement on its website.
Between May 22 and May 28, six people died at the No 2 Hospital affiliated with Nanchang University in Jiangxi province, after being injected with immune globulin, which is derived from blood plasma, the Xinhua News Agency reported Monday.
The drug is widely used to enhance the immunity of critically ill patients, such as those suffering from cancer.
An investigation into the medicine, produced by Jiangxi Boya Bio-Pharmaceutical Co, is ongoing, Yan Jiangying, spokeswoman for the SFDA told China Daily, without giving details of the irregularities mentioned in the statement.
"It will take time to determine the root cause because of the complicated lab tests," she said, while suggesting there was a possibility that counterfeit drugs may have been to blame.
The SFDA has ordered drug suppliers and hospitals to suspend the sale and use of all immune globulin products labeled or sold as products from the Jiangxi company, which was last week ordered to recall the problem drugs, Yan said.
"The provincial police are also involved in the investigation," she said, adding that more information will be published as soon as possible.
There have been no reports of other fatalities, even at hospitals using drugs from the same batch, she said.
Yu Feng, spokeswoman for the hospital where the six people died, told China Daily they were all inpatients who were critically ill.
"Nearly all of them died suddenly, after being on the medicine for two to three days and not showing any adverse signs," she said.
The hospital last month bought 500 units of the drug, she said, and six of the seven patients who had been injected with it died.
"We are puzzled by the deaths, as our hospital has been using the drug produced by the company for years, without any adverse effects being detected," Yu Feng said.
The hospital uses immune globulin supplied only by Jiangxi Boya, which is an approved company and therefore overseen by the SFDA, she said.
Also, as one of the main hospitals in the city, "we strictly abide by drug safety regulations in terms of their proper purchase and use," she said.
In July of last year, the SFDA revoked the production license of Guangdong Baiyi Pharmaceutical Co, which made immune globulin products from infected blood, Xinhua reported.
Some patients injected with the drug tested positive for hepatitis C.
In an effort to increase drug safety, the SFDA in January also began compulsory testing on all batches of blood products and stationed inspectors at each of the country's 33 blood-related drug producers.