The Department of Corrections said it has gone to great measures to ensure only the approved drugs will be used whenever lethal injections resume.
DOC Director Scott Crow says the state's new execution protocol does not allow for any substitutions to the lethal drug cocktail.
The three drugs include Midazolam, a sedative; Vecuronium Bromide, a paralytic; and potassium chloride, which stops the heart.
Federal public defenders argue Midazolam is unreliable and ineffective in sedating prisoners during the execution process.
"The paralytic is a drug that masks what goes on during the execution it paralyzes the prisoner, so by eliminating it, the witnesses would be able to observe how the Midazolam works or doesn't work. However, the court denied our request to have the paralytic removed," said Dale Baich, Federal Public Defender.
In 2014 witnesses described Lockett writhing on the gurney and crying out in pain.
Crow blames Lockett's botched execution on issues with the IV placement.
Then in 2015, Death row inmate Richard Glossip was just hours away from execution before prison officials realized they received the wrong lethal drug.
Oklahoma has not executed anyone on death row since then.