Regulators need to learn more about the excessive sedation triggered in some patients by a longer-lasting version of Eli Lilly and Co.'s top-selling drug Zyprexa before they can approve the treatment.
The U.S. Food and Drug Administration delivered a "not approvable letter" to Lilly for Zyprexa long-acting injection, the company announced Thursday.
It treats adult schizophrenia patients by delivering an injectable dose that can last up to four weeks, as opposed to the once-daily pill currently available for Zyprexa.
Lilly says people suffering from schizophrenia often have a hard time staying on a daily treatment plan and may be helped by getting a monthly injection instead.
The drug maker said about 1 percent of patients in clinical trials experienced excessive sedation. That can be marked by a range of symptoms including drowsiness and slurred speech. Some patients also can wind up in a coma-like state for hours after taking the drug.
All of those patients recovered fully.
Lilly scientists have speculated that the condition is caused by doctors incorrectly injecting the drug directly into the bloodstream, instead of into the muscle. They say when the drug is injected appropriately it dissolves into the body over days and weeks, but when it is injected into the bloodstream it is absorbed over a few hours.
Lilly representatives said in a statement that they were disappointed by the decision but are committed to "ongoing discussions" with the FDA about the issue.
Lilly had proposed calling the treatment Zyprexa Adhera but has since dropped that name after FDA negotiations.
The FDA letter surprised analyst Les Funtleyder, who covers Lilly for Miller, Tabak & Co. He said the agency hasn't expressed many concerns about longer-acting drug forms.
"It's definitely a negative," he said.
Dr. Jon LeCroy, an analyst for Natixis Bleichroeder Inc., said analysts had already factored revenue from the longer-lasting Zyprexa into their projections for this year.
Zyprexa rang up $4.8 billion in sales last year. LeCroy expected annual revenue from the longer-lasting version to grow to about $550 million by 2012.
"Historically, a non-approvable letter has meant death for most drugs," he said. "It doesn't always mean that's always the case, but typically that means that the FDA is requesting completely new trials."
Lilly shares fell 1.7 percent to $50.93 Thursday from Wednesday's closing price of $51.83.