(AP) -- Federal regulators are investigating the deaths of two patients who received injections of a longer-lasting version of Eli Lilly's antipsychotic Zyprexa.
The Food and Drug Administration said Tuesday that the patients died three to four days after receiving an appropriate dose of the drug known as Zyprexa Relprevv. They had very high levels of olanzapine in their blood. That is the chemical compound behind Zyprexa.
High levels of olanzapine can lead to cardiac arrest, irregular heartbeats, sedation or comas.
Lilly spokesman Morry Smulevitz said in an email the drugmaker cannot conclude whether the deaths were related to the drug's administration, but Lilly is still studying the issue.
An FDA representative said doctors can continue to use the drug as long as they follow the plan for administering that comes with it. The plan calls for patients to be monitored for three hours at the site where they received the injection and then accompanied home by someone.
The FDA approved Zyprexa Relprevv in 2009 for the treatment of schizophrenia in adults. The injections can last two to four weeks as opposed to daily versions of Zyprexa. Eli Lilly and Co. has said the longer-lasting version makes it easier for patients to stay on their medication.
The longer-lasting version of Zyprexa generated less than $60 million in revenue last year for Lilly, while the Indianapolis company brought in a total of $22.6 billion.
Zyprexa is Lilly's all-time best selling drug. Its sales once topped $5 billion annually but plunged after it lost U.S. patent protection in late 2011. That exposed the drug to cheaper generic imitations. Zyprexa Relprevv is covered by a different patent that hasn't expired.
Lilly shares fell 12 cents to $52.24 in Tuesday afternoon trading. The stock price has ranged between $41.41 and $58.40 over the past year.