ATLANTA -- Lawyers for a Georgia death row inmate argue the state's lethal injection drug will cause him unconstitutional suffering and that execution by firing squad is the only appropriate alternative.

J.W. Ledford Jr. is set to be put to death Tuesday by injection of the barbiturate pentobarbital. The 45-year-old was convicted of murder in the January 1992 stabbing death of his neighbor, Dr. Harry Johnston.

Ledford's lawyers say his chronic nerve pain has been treated with the drug gabapentin for more than a decade. They cite experts who say exposure to gabapentin alters brain chemistry in a way that pentobarbital cannot be relied upon to make him unconscious and insensate. They say that means there's a substantial risk he'll experience great pain as the drug attacks his respiratory system.

"If you don't know how much pentobarbital to give, you shoot him up with pentobarbital it could make a zombie out of him. It could make him have a stroke to where he becomes totally incapable of movement. You don't know what the effect will be unless you know how much of that drug to give him," said Michael Mears, law professor at John Marshall Law School.

According to the Death Penalty Information Center, Utah, Mississippi and Oklahoma are the only states that have firing squad as an option.

"There are all kinds of ways to kill someone. But the issue is how do you kill them, in the name of the state, without violating the 8th amendment," Mears said.

Ledford is scheduled for execution at 7 p.m. on May 16 at the Georgia Diagnostic and Classification in Jackson, Ga.

Last year, Georgia led the nation with nine executions. Ledford would be the first person executed this year.

Here's what Ledford has requested as his final meal.

Content from the Associated Press contributed to this report.