LITTLE ROCK, Ark. (KTHV) -- At the heart of the federal court challenge to Arkansas’s death penalty protocol is a drug called “midazolam.”

It’s the latest battleground in the 50-year debate over capital punishment in the United States. With Arkansas planning to execute seven inmates before its supply of the sedative runs out at the end of April, the issue is moving the state to the international stage.

“It's a central nervous system depressant,” said Dr. Mike Martin, a medical doctor and professor at University of Central Arkansas. “[Midazolam] is in the same drug class as valium, and it's used primarily as a sedative in minor surgeries like having your tooth extracted.”

This drug designed for causing relaxation is the reason for a great tension. Midazolam will be the first drug injected into the veins of condemned prisoners in the Arkansas three-drug “cocktail.” Two drugs after that stop the prisoners breathing and then the heart.

“The cocktail is meant to do it as rapidly as possible,” Martin said.

At least that's the plan.

But midazolam has never been used in Arkansas in executions, and no state has ever successfully executed two inmates in one day using the sedative.

It's replacing a different class of drugs at the start of the process. Anesthetics like sodium pentothal were first used, but they are now virtually impossible for states to get for capital punishment.

So far, a handful of states have tried Midazolam, but in at least four cases, the sedative proved less effective at rendering the inmate unconscious, which left the prisoner feeling the pain of the other two drugs. The inmates slowly suffocated and eventually died of heart attacks

“If the goal is to be as humane as possible, I think the sodium pentothal may be a little more effective,” said Martin.

That effectiveness and how much pain is endured are important legal questions, and the Eighth Amendment of the Constitution forbids cruel and unusual punishment.

The most dramatic of the four botched midazolam cases came in Oklahoma.

Source: Arkansas Department of Corrections

Clayton Lockett took two hours to die, groaning and struggling as the midazolam failed.

The case led to a later U.S. Supreme Court case and in 2015, the justices ruled in a 5-4 decision that the pain caused in midazolam lethal injections was constitutional.

Since 2013, there have been 17 midazolam executions, almost all in Florida, which first began using midazolam with the first one among those considered “botched” by anti-death penalty advocates. Three states put executions on hold after problems and are keeping the midazolam debate alive.

Different experts are delivering opinions before state and federal judges, and so far, the science has failed to clearly decide the matter.

“I think pentothol may have a more anesthetic effect, but midazolam certainly has an anesthetic effect as well,” Martin said.

Arkansas has had at least two other modern-day lethal injection executions get “botched.” Both involved difficulty finding veins to attach the IV for the drugs, not the drugs themselves.