Oklahoma is running low on supply of drug used in lethal injections

Department spokesman Jerry Massie said the U.S. firm who makes pentobarbital — a fast-acting barbiturate originally designed to sedate animals — has stopped selling the drug to institutions that perform executions.

Pentobarbital is the first of three drugs administered to a condemned prisoner, causing unconsciousness.

It's followed by vecuronium bromide, which stops respiration. Potassium chloride, which stops the heart, is the final drug injected.

In December 2010, Oklahoma became the first state to use pentobarbital during an execution of a human being.

Sodium thiopental, the drug most states had used until then, had become impossible to get.

It remains unavailable today, Massie said.

John David Duty, who was 58, was injected with pentobarbital on Dec. 16, 2010. He was on Oklahoma's death row for strangling his cellmate 10 years earlier.

Prison officials said pentobarbital performed as expected, and Duty was declared dead in minutes.