(CNN) -- An Ohio man is set to be put to death Thursday by a two-drug cocktail never before used in a U.S. execution.
Dennis McGuire was convicted in 1994 of the aggravated murder of Joy Stewart in Preble County, according to the state's governor, who has denied a request for clemency.
Like many states, Ohio has been forced to find new drug protocols after European-based manufacturers banned U.S. prisons from using their drugs in executions -- among them, Danish-based Lundbeck, which manufactures pentobarbital.
Ohio ran out of pentobarbital in September, according to JoEllen Smith, spokeswoman for the Ohio Department of Rehabilitation and Correction.
In response to that shortage, the department amended its execution policy to allow for the use of midazolam, a sedative, and hydromorphone, a painkiller, she said.
The combination has never before been used in a U.S. execution.
"Lawyers for McGuire contend that he will suffocate to death in agony and terror. The state disagrees. But the truth is that no one knows exactly how McGuire will die, how long it will take or what he will experience in the process," Elisabeth A. Semel, clinic professor of law and director of the Death Penalty Clinic at U.C. Berkeley School of Law, wrote in an opinion piece for CNN this week.
The state was set to execute Ron Phillips using the two-drug cocktail last year, but Ohio Gov. John Kasich granted the convicted killer a stay of execution pending a review of possible organ donation to his family members.
Unless there is court action or a reprieve, McGuire will be executed at the Southern Ohio Correctional Facility in Lucasville.
There are currently 139 men and one woman on death row in Ohio, according to the corrections department website.
CNN's Ross Levitt and Deborah Feyerick contributed to this report.