WASHINGTON (AP) — The maker of OxyContin says it has completed testing of an abuse-resistant version of the painkiller hydrocodone, a surprise development that could derail sales of the recently launched Zohydro, which has been heavily criticized for lacking such safeguards.

Purdue Pharma says it plans to submit its pain reliever to the Food and Drug Administration later this year. The company's tablets are designed to prevent users from crushing them for snorting or injection.

Shares of Zogenix Inc. plunged more than 18 percent on the news. A hard-to-abuse form of hydrocodone would be much more likely to garner prescriptions from physicians. And the Food and Drug Administration could potentially pull Zogenix's drug off the market if regulators determine that a safer alternative is available.

Zogenix began shipping Zohydro to pharmacies last week.

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