One of the heart medicines that caused over 100 deaths in Pakistan's Punjab province was contaminated, said a media report citing a British laboratory report.
The samples of Isotab tablet that were sent to a laboratory in London were found to be substandard and injurious to health, reported Geo News.
The drug scandal broke out in Lahore's Punjab Institute of Cardiology.
The Isotab samples were heavily contaminated with Pyrimethamine, a commonly used antimalarial drug, the laboratory report said.
Experts are of the opinion that Pyrimethamine may be causing deadly reactions that are killing cardiac patients who use the tainted life-saving drugs.
Traces of antimalarial in the samples of Isotab were dangerously high, it added.
Punjab chief minister Shahbaz Sharif held a meeting after receiving the report. Health department officials told him that an antidote had been found.
Pakistan President Asif Ali Zardari last week sought a report into the deaths at the Lahore heart hospital.
The government sent samples of the medicines to France and Britain for analysis.