F.D.A. Rejects Request to Block Sales of Generic Painkiller

The Food and Drug Administration announced Friday that generic versions of the painkiller Opana ER can remain on the market, dealing a blow to the brand-name manufacturer, Endo Health Solutions, which had asked the agency to declare the generic versions unsafe.

The agency also ruled that a newer, so-called tamper-resistant form of the drug sold by Endo could be misused by cutting, grinding, chewing or injecting it. Endo had asked the F.D.A. to require that older, generic forms of the drug — which did not have such tamper-resistant properties and entered the market this year — be withdrawn.

The agency’s decision came just weeks after it reached the opposite conclusion in the case of another frequently abused painkiller, OxyContin. In that case, the F.D.A. said it would not approve generic versions of OxyContin since the maker of that drug, Purdue Pharma, had introduced a new tamper-resistant formulation in 2010 that appeared to be less prone to abuse than the generic versions. The patent for the original version of OxyContin expired in April.

The agency is closely scrutinizing efforts by drug makers to develop drugs that are designed to deter abuse. This year, it released guidelines for drug makers seeking to make such drugs and has said it will work closely with companies, including Endo, that want to do so. But an agency official, Dr. Douglas C. Throckmorton, said in an interview on Friday that the F.D.A. had to ensure that these products actually worked.

“We believe that the public health value of concluding that a product is abuse-deterrent is very important,” said Dr. Throckmorton, who is deputy director of regulatory programs for the agency’s Center for Drug Evaluation and Research. However, he added, “It is very important to us to make sure that products that have that claim do so as the result of substantial scientific evidence.”

The agency said it found the reformulated Opana did prove resistant to crushing — abusers typically seek to crush or pulverize the product to release the drug’s narcotic payload — but it could still be cut, ground or chewed. The new Opana ER can also be injected or snorted, “using commonly available tools and methods.”

A spokesman for Endo did not return a call for comment on Friday. The company’s stock was down more than 5 percent at the close of trading Friday, to $34.98.