Arizona inmate slated for lethal injection; will get a single dose of pentobarbital

We're learning more about the lethal injection drug that will be used next month for an inmate on death row. Clarence Dixon is set to be executed on May 11 in what would be Arizona's first use of the death penalty in nearly eight years.

Earlier this week, Dixon declined to pick a method of execution when officials asked him whether he wanted to die by lethal injection or the gas chamber. Since he did not give an answer, the default is lethal injection.

Dixon was convicted of the 1978 murder of Arizona State University student Deana Bowdoin.

The last time Arizona used the death penalty and lethal injection was in July 2014 when Joseph Wood was given 15 doses of a two-drug combination over two hours. Lawyers say that execution was botched, but this time, for Dixon, he will be given the single dose pentobarbital drug.

Clarence Dixon

Clarence Dixon (Arizona Department of Corrections)

"We know that it has been successful in taking the lives of prisoners. It's been used in numerous executions. The question always is the potency the purity, is it contaminated? If it's not pure, it's still going to be torturous," said Robert Dunham, Executive Director of the Death Penalty Information Center.

But the drug has a short shelf life -- about 45 days and experts say it doesn't always work.

"The same amount of one drug may do what it's supposed to do with one person and not do what it's supposed to do with another. That is one of the inherent issues with capital punishment. Because prisons set a particular dosage and they don't vary it depending on the weight of the prisoner, where the prisoner's medical history is," explained Dunham.

States are finding it increasingly difficult to secure lethal injection drugs as manufacturers refuse to make them.

MORE: ADCRR says it's prepared for executions after obtaining necessary drugs

Arizona has found the drug from smaller compounded pharmacies that make the drugs on site.

Pentobarbital has many uses. In small doses, it can treat anxiety and seizures, as well as help patients relax before surgery. In higher doses, it's used for veterinary euthanasia and for death penalty executions.

"If they’ve done it properly, a single dose should work and the prisoners should become unconscious relatively quickly and should die anywhere in the range of six to 10 minutes," said Dunham.

Prosecutors believe the execution will likely be delayed if a judge goes forward with a hearing to determine whether Dixon is mentally fit to be put to death.

At last check, Arizona has 112 prisoners on death row.

Only 3 women are on Arizona's death row: Who are they and what were they sentenced to death for?

Currently, an overwhelming majority of the people in Arizona's death row are men, with only three women amongst them. Here's what you should know about the women who have been sentenced to death in Arizona, and what they did that led to them being sentenced to death.