The Oklahoma State Penitentiary has used a veterinary anaesthetic drug called pentobarbital, more commonly used to put down dogs, to execute John Duty (58), a prisoner on death row.

In a development that is likely to fuel the ongoing arguments on whether the lethal injection method of execution constitutes “cruel and unusual punishment,” the state used the animal drug in place of sodium thiopental, one of the three chemicals injected as part of the procedure.

Duty was pronounced dead at 6:18 p.m. eastern standard time according to Jerry Massie, a spokesman for the Oklahoma Department of Corrections. He had been sentenced to death for strangling his cellmate, Curtis Wise, back in 2001.

Earlier this year the sole manufacturer of sodium thiopental in the United States, a company called Hospira, ran out of stock and said that it did not expect to resume production until 2011.

Last month Oklahoma state lawyers petitioned U.S. courts for use of the veterinary euthanasia drug in place of sodium thiopental, describing it as “an ideal anaesthetic agent for humane euthanasia in animals,” and not substantially different to sodium thiopental, according to reports. On November 19, Oklahoma federal judge Stephen Friot authorised the state’s use of the drug.

However numerous capital punishment specialists were reported to have warned that pentobarbital “had not been properly vetted and might not keep inmates unconscious during the more painful subsequent injections that kill them.”

In particular Duty’s lawyers had argued that that he would be used as a “guinea pig” in an experiment with the animal anaesthetic. While the anaesthetic is administered first, to cause unconsciousness, pancuronium bromide is then administered to induce paralysis, and finally potassium chloride is injected to stop the heart from beating.

In a different case, the Guardian newspaper reported, post-mortem examinations of three recent executions in Tennessee showed that there was “insufficient anaesthetic in the prisoner’s bloodstream: he was not rendered unconscious.” The newspaper said that in those cases the inmates did not die painlessly but “slowly suffocated as the other drugs took effect, an excruciating death.”

This year the debate surrounding the shortage of sodium thiopental spilled over international borders as well, with the United Kingdom coming in for a barrage of criticism from death penalty abolitionists in Europe, for exporting sodium thiopental to authorities in Arizona, who subsequently used them to execute another inmate, Jeffrey Landrigan.

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