A man on Oklahoma's death row for the 2001 slaying of his cellmate is believed to be the first US inmate set to be executed using a sedative commonly used to euthanise animals.
John David Duty is set to die at 0000 GMT on Friday at the Oklahoma state penitentiary in McAlester. A federal appeals court earlier this week upheld a judge's ruling that allows the state to substitute
pentobarbital for sodium thiopental, an anaesthetic normally used in the state's lethal injection formula.
A nationwide shortage of sodium thiopental led Oklahoma to alter its three-drug cocktail.
Attorneys for Duty, 58, and two other death-row inmates challenged the state's decision to use pentobarbital, arguing during a November federal court hearing that it had not been done before in executions and could be inhumane.