In a surprise move, federal health regulators have denied a request by Endo Health Solutions to block generic versions of its painkiller Opana ER, which the company argued can be more easily abused than its branded product.

Endo's Opana ER is a long-acting narcotic used to treat moderate and . Such medications are frequently crushed and then injected or snorted by drug abusers to achieve a euphoric effect.

Last year, Endo reformulated Opana with the aim of making the pills more difficult to crush. The company also hoped the move would protect its expiring patent on Opana by blocking approval of based on the original formulation.

But the FDA said late Friday that it denied the petition, pointing out that Endo's reformulated drug can still be abused.