ATLANTA – A death row inmate’s federal lawsuit claims Georgia’s stockpile of a key lethal injection drug has expired, and he’s asking a judge to halt an execution he says may cause him to die in excruciating pain.

The lawsuit filed Friday on behalf of Roy Willard Blankenship raises new questions about Georgia’s supply of sodium thiopental, a sedative that has been in short supply even before the drug’s sole U.S. manufacturer decided last month to stop producing it.

“No matter where Georgia obtained its supply of the drug, the drug is almost certainly expired and no longer effective,” said the lawsuit, which was filed in U.S. District Court by the Atlanta-based Southern Center for Human Rights.

The shortage has delayed executions in several states, and an Associated Press review found that at least five states — Arizona, Arkansas, California, Georgia and Tennessee — had to turn to England for their supply of the drug. Nebraska, meanwhile, secured a stockpile from an Indian firm.

Georgia corrections officials did not respond to a request for comment. But state attorneys have said the drug expires in February 2014, and that the same batch of drugs was used without problems for earlier executions in Georgia and Arizona.

Blankenship was set to be executed last Wednesday for the 1978 murder of an elderly woman, but the state pardons board postponed it earlier this month to give authorities more time to conduct DNA testing on the victim’s remains. The lawsuit urged the judge to call off the execution until the state releases more details of the state’s supply of the drug. Get more information by Clicking Here.

Sodium thiopental is a barbiturate used by most states as part of a three-drug cocktail. It puts inmates to sleep before officials administer pancuronium bromide, which paralyzes the muscles, and potassium chloride, which stops the heart. The lawsuit contends that the expired drug may not fully put Blankenship to sleep — which could make his death extremely painful as the other drugs take effect.

The lawsuit, citing state documents, claims the sodium thiopental is stored in vials labeled “Link Pharmaceuticals,” a firm purchased five years ago by Archimedes Pharma Limited, another British company.

Link Pharmaceuticals didn’t exist in 2010, and its name hasn’t been on labels since May 2007, the lawsuit said. Sodium thiopental typically has a shelf life of four years, meaning even the state’s newest supply would expire in May of this year, according to the lawsuit.

Archimedes did not immediately respond to a request for comment. But it has said the firm does not export the drug to the U.S. and that it doesn’t keep information on the purchasers and users of its products.

Blankenship’s lawsuit also includes an affidavit from Randall Tackett, a University of Georgia pharmacy professor, who said using an expired batch of the drug could have grave consequences.

“There is an extremely high risk that the use of expired sodium thiopental would cause the individual being executed to experience excruciating pain due to inadequate sedation,” he said.t