WASHINGTON – Government regulators dealt a major setback to Schering-Plough Corp. Thursday, rejecting a highly anticipated drug designed to help patients recover from anesthesia.

The Food and Drug Administration notified the company that it will not approve its drug sugammadex, due to concerns about allergic reactions seen in some patients, according to a company statement.

Schering said it was “surprised and disappointed” by the decision but would “work with the agency to address the issues.”

Schering's shares fell on the news, lose $1.37, or 6.5 percent, to $19.71 Friday morning.

The rejection letter was unexpected because a panel of outside FDA advisers had unanimously voted in favor of the medication earlier this year. The FDA is not required to follow the group's advice, though it usually does.

And on Tuesday, European Union regulators cleared the injectable drug, which is designed to reverse the effects of anesthesia in patients after surgery. The drug will be marketed in Europe under the name Bridion, though a commercial name has not been selected for U.S. promotion.

Surgeons typically use muscle-paralyzing anesthetic drugs to make surgery easier and safer for patients.

Despite positive reviews from some experts, FDA scientists voiced safety concerns with sugammadex in their initial review. According to the documents released in March, FDA said additional safety studies could be needed to examine allergic reactions seen in some patients.

However, company representatives argued that the drug's benefits more than outweigh those risks.

Dr. Ronald Miller, a consultant for Schering, said that sugammadex works better than existing treatments, which carry their own negative side effects, including heart problems and nausea.

“The drugs we currently use produce many more reactions and much more severe reactions than anything that has been demonstrated with sugammadex,” said Miller, who chairs the department of anesthesia at the University of California at San Francisco. “I was quite disappointed with the FDA ruling.”

FDA has rejected several drugs this year that were expected to gain approval, including an allergy drug combining the ingredients of Schering's Claritin and Merck & Co. Inc.'s Singulair tablets.

Some analysts have speculated that FDA has become more cautious about putting new drugs on the market following the safety concerns around drugs like Merck's painkiller Vioxx and GlaxoSmithKline's diabetes drug Avandia. In both cases, there were older medications on the market with more established safety profiles.

Currently there are two anesthesia-reversing drugs on the market that surgeons have used for decades.