A federal judge in Ohio has approved the state's plan to kill convicted killer Dennis McGuire by using an untested mixture of drugs that his lawyers, informed by experts, say could leave the man writhing in pain from the "agony and terror of air hunger" as his lungs shut down.

A state prosecutor in the case told the court that McGuire—convicted in the rape and murder of a woman named Joy Stewart in 1989—"is not entitled to a pain-free execution" as he won the case before presiding Judge Gregory Frost.

“Ohio is free to innovate and to evolve its procedures for administering capital punishment," Frost said in his ruling against McGuire's lawyers who were pushing for a stay of exectuion based on the use of the un-tested drugs.

Ohio plans to use a dose of midazolam, a sedative, combined with hydromorphone, a painkiller, to put McGuire to death, but his lawyers contend that the unproven combination could result in extreme pain. McGuire could be put to death as early as Thursday.

The situation stems from a shortage of other drugs tradtionally used in lethal injection executions. As the Guardian's Ed Pilkington describes:

Ohio's use of the new two-drug combination is a move of desperation, one forced by shortages of the anaesthetic pentobarbital that had been relied upon in the three-drug cocktail used for executions by lethal injection all over the US. The approved supplies of pentobarbital in death penalty states across the US have all passed their expiration dates following European restrictions on exportation of the substance and a strict prohibition of sales to prison services imposed in 2011 by the drug's Danish manufacturer Lundbeck.

The dearth of approved pentobarbital may also lie behind a disturbing event at an execution in Oklahoma last week that could provide a preview of what will happen when states turn to new procedures as Ohio has. On Thursday, Michael Lee Wilson, 38, was put to death amid evidence that the procedure caused him considerable pain.

About 20 seconds into the execution, Wilson uttered what were, according to an Associated Press reporter who witnessed the execution, his final words: “I feel my whole body burning”.

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