Shares of Alkermes PLC tumbled more than 44 percent Thursday after the Irish-based drug maker, which has a 450-person research lab in Waltham, reported the failure in clinical trials of an experimental drug to treat a form of depression.
The company reported the setback in a pair of late-stage studies of its lead drug candidate, called ALKS 5461, a daily pill developed to treat major depressive disorder in patients who have not responded to existing treatments. The news slashed nearly $4 billion off Alkermes's market value.
In one study, the drug compound didn't meet its primary goal, known as an endpoint, but proved more effective than a placebo when given at a high dose. The drug showed no measurable effect on patients in the second study, underperforming the placebo.
Alkermes, which markets drugs to treat schizophrenia, drug addiction, and alcohol dependence, released a statement pointing to some encouraging data from its ALKS 5461 trials. It said it would press forward with a third study testing the drug on more patients.
"We are building a large body of evidence supporting our belief in the clinical utility and the novel mechanism of action of ALKS 5461," Alkermes chief executive Richard Pops said in the statement. Pops did not respond to a request to discuss the clinical results.
Shareholders had high expectations that Alkermes had developed an effective treatment for a disease that afflicts more than 15 million Americans. Investors sent the company's shares down $26.71 to $33.71, a 44.2 percent drop on the Nasdaq stock exchange Thursday.
Alkermes, founded in 1987, went public in 1991. It was based in Waltham until 2011 when it merged with Elan Drug Technologies, an arm of Dublin drug maker Elan Holdings PLC, in a $960 million "inversion" deal that transferred Alkermes's corporate headquarters to Ireland, where corporate taxes are lower than in the United States.
While the company has a research and manufacturing complex in Athlone, Ireland, it retains its research and development lab in Waltham along with a second manufacturing plant in Wilmington, Ohio. Alkermes has about 1,500 employees worldwide.