Substandard generic drugs are putting the lives and health of heart patients at risk, researchers said Tuesday. A study of 21 samples of a clot-busting drug used to treat Heart attack patients showed that only three formulations performed as listed on the label.

The drugs, known as streptokinase, belong to a group of medicines called fibrinolytics that are used immediately after a heart attack.

“The most striking finding of this study was the significant discrepancy between claimed and measured streptokinase activity of the majority of the tested products,” said Dr. Michael Thimme, of Aventis Behring in Marburg, Germany, in a study published in the European Heart Journal.

“We were very surprised by what we found,” he added in an interview.

Aventis Behring was acquired last year by Australia’s CSL Ltd.

A generic drug is a copy of a brand-name drug that is no longer under patent. Generics use the same active ingredients and work in the same way in the body. The scientists said the activity of the drugs they tested varied from 107 percent of the claim on the label to just 20 percent. Under European rules, drug activity must be 90-111 percent of what is claimed. There were also differences in the composition and purity of the drug.

The activity of the drug is important because if the dose is too low, it won’t restore blood flow to the artery. If it is too high, a dose could cause bleeding in the brain.

“The discrepancy between claimed and actual activity of many streptokinase preparations could cause life-threatening situations in severely ill patients,” Dr. Peter Hermentin, a co-author of the study, said in a statement.

The generic drugs tested in the study were made by 11 pharmaceutical companies, including Aventis Behring, based in six countries: Korea, Germany, Sweden, India, China and Cuba.

One distributor was European while the others were in India, Pakistan, Brazil, China and Jordan. The researchers said the problem did not result from transport or storage problems.

In an editorial in the journal, Dr. Felicita Andreotti and Filippo Crea of the Catholic University in Rome, Italy said sub-standard and counterfeit drugs are a major problem and a global responsibility.

“Indeed the World Health Organization estimates that up to 10 percent of the world’s drug trade - 25 percent in developing countries - consists of fakes that are sold around the world,” they said.

“Control of this phenomenon clearly constitutes a global challenge,” Andreotti and Crea added.

Drugs to treat malaria, tuberculosis and AIDS are often the object of counterfeiters.