(Adds background, share reaction)
Oct 12 (Reuters) - Collegium Pharmaceutical Inc said the U.S. Food and Drug Administration said it would not be able to complete its review of the company's opioid painkiller by Monday.
The company's shares fell 8 percent in extended trading.
Collegium did not say if the FDA had given any reason for not being able to complete the review by the set date of Oct. 12 or when it expected the review would now be completed.
Collegium's long-acting experimental oral opioid painkiller, Xtampza, is meant to be taken after a meal for maximum effect.
A panel of outside advisers to the FDA had unanimously voted in favor of the drug on Sept. 11. But, two days before that FDA staff had said that if the drug was taken without food, it could give insufficient relief, which could lead to overdosing.
The abuse of opioids - a class of drugs that include heroin and prescription painkillers - has long been a concern. An overdose of such drugs can produce euphoric highs and even disrupt parts of the brain that control breathing.
The FDA's ruling on Xtampza will be keenly watched by other developers of abuse-deterrent versions of painkillers.
These include Pernix Therapeutics Holdings Inc, Egalet Corp, KemPharm Inc, Pain Therapeutics Inc and Acura Pharmaceuticals Inc.
Collegium's shares were trading at $18.25 after the bell. They closed at $20.09 on the Nasdaq.
(Reporting by Rosmi Shaji in Bengaluru; Editing by Savio D'Souza)