Regulators are asking for more time to review Celgene's ( CELG) Revlimid safety program before deciding whether to approve the drug for patients with certain blood disorders.

The Food and Drug Administration has decided to extend the action date for its review of the Revlimid new drug application to Jan. 7, according to a notification the company received Friday. The FDA action date for Revlimid originally was set for this Friday, but the agency plans to review additional information on Celgene's "RevAssist" risk-management program.

The RevAssist program is designed to observe Revlimid's toxicity and the chances that the drug will cause birth defects, a measure known as teratogenicity. The RevAssist plan, according to Celgene, includes physician education, limited Revlimid distribution and interim pregnancy testing before and during treatment.

Revlimid is proposed to treat anemia associated with certain mild to moderate myelodysplastic syndromes, a group of blood and bone marrow sicknesses. The drug is closely related to thalidomide, a drug associated with severe birth defects when it was used in Europe and Canada to prevent morning sickness in the 1960s. Thalidomide, also known by Celgene's brand name Thalomid, is currently approved to treat leprosy but is more commonly used as an off-label treatment in patients with multiple myeloma, a blood cancer.

The additional information provided to the FDA on the RevAssist program "has been considered by the FDA to be a major amendment to the Revlimid NDA allowing the extension of the action date under PDUFA regulations," the company wrote in a press release.

In a conference call Monday morning, Celgene said the extension is only a short-term delay, and it won't materially affect launch preparations or the company's application for the drug's use in multiple myeloma, which is on track for a November submission.

Based on conversations with the FDA, Celgene doesn't expect that its overall timelines for the drug will be significantly affected, Chief Financial Officer Bob Hugin said during the company's conference call.

Celgene also has completed additional studies on Revlimid's teratogenicity in rabbits, "but no action is dependent on these studies," said Sol Barer, the company's chief operating officer.

As far as teratogenicity in humans, "Obviously you can't really do the trial in patients, so you never really know," says Celgene spokesman Brian Gill. The RevAssist program is designed to eliminate fetal exposure to the drug, he says.

Last month, the FDA's oncologic drug advisory committee recommended full approval of Celgene's Revlimid for patients with myelodysplastic syndromes. The FDA isn't required to follow the committee's recommendation, but often does.

Celgene shares closed Monday at $54.58, up 26 cents, or 0.5%.

As originally published, this story contained an error. Please see Corrections and Clarifications.

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