(Corrects analyst's name in 12th paragraph to Smith from Cox)
By Susan Heavey
WASHINGTON, March 28 (Reuters) - Officials in Massachusetts have blocked sales of Zogenix's controversial but U.S.-approved painkiller Zohydro, prompting the drugmaker to criticize what it called an "unprecedented action."
The state's ban "only serves to unfairly restrict patient access," the company said in a statement late Thursday. "Ultimately, the ban on the prescription medication will add to patient suffering in the state," it added.
Massachusetts Governor Deval Patrick announced the Zohydro ban in a speech on Thursday, formally declaring a public health emergency resulting from the abuse of opioids in the New England state.
It is the latest salvo in the ongoing battle over Zohydro's launch as the U.S. grapples with a wave of abuse of opioids, a class of drugs that includes not only powerful prescription painkillers but also heroin.
On Friday, shares of the San Diego, California-based company were down 4 percent in early afternoon trade on the Nasdaq.
The federal Food and Drug Administration approved Zohydro last year over the objections of its advisory panel, which expressed concerns about the potential for abuse.
The drug has since come under further scrutiny from members of Congress, dozens of state attorney generals, medical groups and drug treatment experts seeking to block the drug even as the FDA's top official has defended its action.
While the FDA approves drugs for sale in the United States, it does not guarantee their availability. For example, health insurance companies can exclude certain medications from their formularies.
Zohydro is a form of hydrocodone that, unlike rival products such as AbbVie Inc's Vicodin or UCB's Lortab, does not contain acetaminophen.
The company has defended the drug as a necessary option for pain patients who cannot tolerate acetaminophen, a nonsteroidal anti-inflammatory drug linked to liver damage and stomach bleeding.
But critics worry that with no built-in abuse deterrents, Zohydro will be a draw for addicts looking for an easy fix. Rival Purdue Pharma has said it is working on a hydrocodone-only drug that will be resistant to abuse, something Zogenix has also pledged to do.
"Once/if the Purdue product is approved, possibly in 2015, FDA could then rule that Zohydro is not as safe as the abuse-deterrent product and either pull the drug's approval or ask Zogenix to withdraw it voluntarily," Rob Smith, an analyst with Capital Alpha Partners, said earlier this week.
Zogenix, in its statement, said it would "review the safe use measures already in place" with Massachusetts officials.
(Reporting by Susan Heavey; Editing by Bernard Orr)