CSL says the most ambitious clinical trial in its 107-year history has failed to show any benefit to a highly touted potential treatment aimed at stopping secondary heart attacks.
CSL has spent two decades and nearly $1 billion developing CSL112, a treatment derived from human blood plasma.
But a five-year phase three clinical trial involving 18,200 patients from 49 countries who had suffered a recent heart attack found it was no better than placebo in reducing a second major adverse cardiovascular event in the following 90 days, CSL said.
"As a result, there are no plans for a near-term regulatory filing," the company said in a news release on Monday that sent its shares tumbling five per cent, their worst single-day performance in more than three months.
"Substantial work remains to fully analyse and understand the complete data and then to determine any development path ahead for this asset," said Dr Bill Mezzanotte, CSL's executive vice-president and head of research and development.
CSL had hoped the treatment would be a transformative wonder drug for the company and had even been preparing manufacturing facilities for its production.
About 10 per cent of all heart attack patients have a second cardiovascular event within 90 days, many of which are fatal.
The patients, recruited from 850 sites in 49 countries, had four weekly intravenous infusions of CSL112, which works to boost the body's HDL-cholesterol - the so-called "good" cholesterol that works to remove other forms of the artery-clogging lipoproteins from the bloodstream.
The principal investors are still analysing their findings and plan to present their research at a conference of the American College of Cardiology in April, as well as publish in a peer-reviewed journal.
CSL shares were down 4.4 per cent to $291.50 late on Monday afternoon.
