Ohio will use a two-drug combination untried as an execution method in the U.S. to put to death a condemned inmate who raped and killed a pregnant woman, the state prisons agency confirmed Tuesday.

The determination means the state was unable to obtain an unregulated batch of pentobarbital, the drug Ohio used until its manufacturer put it off limits for executions.

Instead, the state will use drugs from its untested backup execution method in the Jan. 16 execution of Dennis McGuire, according to the decision contained in a memo by Southern Ohio Correctional Facility warden Donald Morgan and released to The Associated Press after a public records request.

The untested method: an intravenous combination of midazolam, a sedative, and hydromorphone, a painkiller. No state has put a prisoner to death with those drugs in any fashion.

It's Ohio's second attempt to use the two drugs in combination. The Department of Rehabilitation and Correction intended to use the method last month to execute a man who raped and killed his girlfriend's 3-year-old daughter.

But that inmate, Ronald Phillips, won a reprieve from Gov. John Kasich while the prisons agency studies the feasibility of his desire to donate a kidney to his mother and his heart to his sister after his death.

The two drugs were part of a backup method in which they would be injected into an inmate's muscle if the intravenous method failed. Because the pentobarbital is unavailable, the two-drug combination will instead be the primary method for execution and injected into McGuire's veins.

McGuire, 53, of Preble County in western Ohio, was sentenced to death for killing Joy Stewart in 1989 after meeting her while working on her friend's house. Investigators say McGuire raped and choked the 22-year-old Stewart and stabbed her in the neck and shoulder. The newly married Stewart was about eight months pregnant.

Ohio's revamped execution policy calls for the state to try to buy specialty batches of pentobarbital from compounding pharmacies, which mix individual doses of drugs for specific patients. If that fails, the policy recommends the use of the two-drug approach.

Florida uses midazolam as the first of three drugs, while Kentucky includes the two Ohio is using in its untested backup method.

The Ohio Parole Board recommended against clemency for McGuire. Kasich has the final say.

McGuire's attorney Rob Lowe said he was consulting with other members of McGuire's legal team and couldn't immediately comment.

Attorneys for McGuire have argued a jury never got to hear the full extent of his chaotic childhood and physical, sexual and mental abuse he suffered.

They also say the fact the state offered him a plea deal -- which McGuire rejected -- should be considered in granting him mercy.

Prosecutors say McGuire deserves the death penalty because of the shocking nature of the crime.