LONDON - AstraZeneca PLC said today that the U.S. Food and Drug Administration has asked for more information regarding the drug Seroquel, which AstraZeneca is trying to get approved for use by people suffering from depression.

Seroquel XR, one of AstraZeneca's best-selling drugs, is currently approved in the United States only for the treatment of people with schizophrenia or bipolar disorder, a disease characterized by dramatic and severe mood swings.

But AstraZeneca has applied to the FDA to market the drug for the treatment of major depressive disorder in adult patients.

The London-based drugmaker, which has a big presence in Delaware, said that FDA has sought more information in a so-called complete response letter (CRL) to that application.

"AstraZeneca is evaluating the contents of the CRL and the proposed labeling revisions," the company said in a statement to the London Stock Exchange. "AstraZeneca will continue discussions with the FDA and will provide a response to the agency in due course."

The company said it did not yet know whether, or when, the drug would get approval for treating depression.

"At this point in time, we don't know if this means that there will or there won't be a delay, or whether this could lead to no approval," said Sarah Lindgreen, spokeswoman for AstraZeneca.

AstraZeneca said the FDA letter does not change the current recommendations for the treatment of patients using the drug for schizophrenia or bipolar disorder.

Seroquel is AstraZeneca's second-best seller behind heartburn drug Nexium, raking in $4 billion (U.S.) in sales last year.

AstraZeneca earlier this year won a key decision in a U.S. court that means that generic copies of the drug will not be launched any time soon.

AstraZeneca's American depositary shares were priced at $39.33, down 39 cents (0.98 percent) on this holiday-shortened trading day.