WASHINGTON (AFP) – Benny Joe Stevens, who was convicted of killing four people, including two children, has been executed by the state of Mississippi with a drug normally used to euthanize animals.

Stevens, 52, was pronounced dead at 6:22 pm (23:22 GMT) at the state penitentiary in the town of Parchman, according to Mississippi prison officials.

It was the first time the southern state had used the sedative pentobarbital instead of sodium thiopental, whose US manufacturer recently said it was no longer making the drug. Pentobarbital is also used in assisted suicides in two US states and as an animal euthanasia.

Mississippi is the latest US state to adopt pentobarbital as part of a three-drug protocol after Louisiana, Oklahoma, Texas and soon Alabama.

Pentobarbital, which produces an unconscious state, is followed by an injection of pancuronium bromide, which paralyzes the inmate, and finally potassium chloride, which stops the heart.

Ohio and the state of Washington use one single, massive dose of pentobarbital. The Danish company that makes the drug, Lundbeck Inc., has said it opposes the drug's use in executions.

The US Supreme Court denied a stay of execution, prison officials said.

Stevens appealed to the Mississippi Supreme Court over the change from sodium thiopental to pentobarbital, but his appeal was rejected last week.

Stevens was condemned to death for the 1999 murder of his ex-wife, Glenda Reid, Reid's husband, Wesley Reid, their 11-year-old son Dylan and the boy's friend Heath Pounds, in a mobile home park in rural Marion County following a custody dispute over Stevens' daughter.

The daughter, Erica, was wounded, and was a witness against Stevens in his trial.