Prosecutors countered that executions need not be free of all pain and that the defense failed to show that Roy Blankenship -- who witnesses say grimaced and jerked -- suffered excessively before he died June 23.
"Some pain is allowed during an execution," Assistant Attorney General Sabrina Graham said at a federal court hearing. "Is it looking at your arm and grimacing, is that unnecessary pain and suffering? It is not."
Defense attorneys are seeking a temporary restraining order to stop the execution of Andrew DeYoung, who is scheduled to die today for the 1993 slayings of his parents and 15-year-old sister.
DeYoung's attorney argues that the state's use of pentobarbital in its three-drug mixture is unconstitutional and violates the ban against cruel and unusual punishment.
Amid questions surrounding the state's lethal injection procedure, a Fulton County judge has ordered that DeYoung's execution be videotaped and submitted to the court under seal. A spokeswoman for the state attorney general said the office was reviewing the order to decide how to proceed.
The state switched to pentobarbital this year after federal regulators took the state's supply of sodium thiopental amid questions about how it was obtained amid a nationwide shortage.
Dr. David Waisel, a Harvard University medical professor and anesthesiologist, testified Tuesday that pentobarbital is largely untested as a stand-alone sedative in humans. The drug is used most commonly to euthanize animals.
Waisel said he reviewed accounts from those who witnessed Blankenship's June 23 executions, including a report by The Associated Press, and said he concluded Blankenship had suffered.
"It is my opinion that during this process Mr. Blankenship exhibited needless pain and suffering," said Waisel, who previously had expressed concerns about the use of pentobarbital.
A key focus of Tuesday's hearing was the account of AP reporter Greg Bluestein, who reported Blankenship jerked his head several times during the procedure, looked at the injection sites in his arms and muttered after the pentobarbital was injected into his veins.
Death penalty critics said Blankenship's unusual movements were proof that Georgia shouldn't have used pentobarbital to sedate him before injecting pancuronium bromide to paralyze him and then potassium chloride to stop his heart. State prosecutors, meanwhile, raised questions about the timeline cited in the AP story and argued Blankenship's movements occurred before the sedative took hold.
In addition, state prosecutors argued that adequate safeguards are in place to ensure inmates do not suffer needlessly, including a consciousness check before the second and third drugs are administered.
With DeYoung's execution set for this evening, U.S. District Court Judge Steve C. Jones said he would rule soon.
DeYoung would become the second person in Georgia to be executed with pentobarbital.
Amid a national shortage of sodium thiopental, states have been turning to pentobarbital to carry out executions. It has now been used this year to put at least 18 inmates to death in eight states.