Merck & Co Inc said on Monday that health regulators are concerned about operational aspects of a hypersensitivity study for sugammadex, an injection designed to reverse the effects of muscle relaxants used by anesthesiologists during surgery.
Merck said on Monday it had received a "complete response letter" from the FDA on its resubmission of sugammadex for approval. Such letters typically lay out U.S. Food and Drug Administration concerns that need to be addressed before a medicine can gain approval.
Merck said it was evaluating the letter and "expects to be able to determine a path forward in the very near future."
In July, the FDA canceled a meeting of outside advisers who were scheduled to vote on whether to recommend the drug for approval. Merck said then that the agency needed more time to assess findings from an inspection of a clinical trial site.
In 2008, the FDA declined to approve sugammadex, citing concerns about its possible association with allergic reactions and bleeding.
BMO Capital Markets analyst Alex Arfaei found a bright spot in the drug's latest delay.
"The FDA concerns in the complete response letter do not seem related to the product's clinical profile. We expect the issues to eventually be resolved," he said in a research note.
Arfaei said he expects U.S. approval of sugammadex by the second quarter of 2014 and forecast worldwide sales of $574 million in 2015.
The drug is already approved in 50 countries, including Japan.
Merck shares were down 0.7 percent at $47.65 late on Monday morning on the New York Stock Exchange.