Despite a shortage of lethal-injection drugs, two of the nation's most active death penalty states have quietly carried on with executions by turning to pentobarbital, a powerful sedative that generally puts inmates to death swiftly and without complications.
Missouri and Texas have avoided the prolonged executions seen in other states where authorities are struggling to find a reliable chemical combination. The drug's apparent effectiveness raises questions about why it has not been more widely adopted.
"There is a better drug, and that better drug is pentobarbital," said Kent Scheidegger, legal director of the pro-death penalty Criminal Justice Legal Foundation.
Lethal injection is in the spotlight after executions went awry in Ohio, Oklahoma and Arizona, which all use midazolam, a drug that is more commonly given to help patients relax before surgery. In executions, it is part of a two- or three-drug lethal injection.
Texas and Missouri instead administer a single large dose of pentobarbital, which is often used to treat convulsions and seizures and to euthanize animals.
Since 2011, more than five dozen executions have been performed solely with pentobarbital, according to records kept by the Death Penalty Information Center in Washington, an advocacy group that opposes the death penalty. In most cases, inmates showed no obvious signs of suffering. Not all, though.
In 2012, South Dakota used pentobarbital to execute Eric Robert, who was convicted of killing a prison guard. As the drug was administered, Robert appeared to clear his throat and gasped heavily, then snorted for about 30 seconds. His eyes remained opened and his skin initially turned pale, then a purplish hue.
Pentobarbital also was the first of three drugs used to execute Michael Wilson in January in Oklahoma. His final words were, "I feel my whole body burning."
Missouri changed to pentobarbital late last year and has since performed eight executions during which inmates showed no obvious signs of distress.
Scott Holste, spokesman for Missouri Gov. Jay Nixon, said the drug has proven dependable for conducting executions "in an efficient, effective and humane manner."
The Texas Department of Criminal Justice is equally confident in its use of pentobarbital, which it adopted in 2012. Since then, the drug has been used in 33 executions without complication, agency spokesman Jason Clark said.
Earlier this year, Georgia also used pentobarbital alone to kill a condemned inmate.
Missouri and Texas both plan two executions during the next six weeks, starting with inmate Michael Worthington, who is scheduled to die Wednesday in Missouri. Worthington's execution would be the first since Joseph Rudolph Wood was put to death last month in Arizona. Wood gasped more than 600 times while he lay on the table and took nearly two hours to die.
Back in January, Ohio inmate Dennis McGuire snorted and gasped for 26 minutes before dying. A few months later, Clayton Lockett died of an apparent heart attack 43 minutes after his April execution began in Oklahoma, where officials have pointed to improper insertion of the needle delivering the drugs.
Most lethal injections kill in a fraction of that time, often within 10 or 15 minutes. Governors in all three states have ordered investigations.
Texas, Florida and Missouri are responsible for 20 of the 26 executions that have taken place so far in 2014. Nationwide, 17 executions are scheduled through December.
For decades, states used the same three-drug formula for lethal injections: a sedative that rendered the inmate unconscious, usually sodium thiopental, followed by a paralytic agent, usually pancuronium bromide, and finally the drug that stopped the heart, potassium chloride.
But in recent years, major drugmakers, many of them in Europe, stopped selling pharmaceuticals for use in executions, citing ethical concerns. By 2011, with sodium thiopental no longer available, Ohio became the first state to use pentobarbital in a single-drug execution.
Soon, the Danish maker of pentobarbital, Lundbeck Inc., initiated efforts to keep it out of the hands of corrections departments. That led Ohio and some other states that initially used the drug to abandon it.
Missouri and Texas have turned to compounding pharmacies to make versions of pentobarbital. But like most states, they refuse to name their drug suppliers, creating a shroud of secrecy that has prompted lawsuits.
It's not clear if other states are considering switching to pentobarbital. Most states refuse to discuss decisions related to execution drugs, and officials in several corrections agencies did not respond to interview requests from The Associated Press.
Executions go wrong for several reasons, said Dr. David Waisel, associate professor of anesthesia at Harvard Medical School, who predicted in a court document prior to McGuire's execution that the process would be prolonged and potentially agonizing.
Waisel cited rigid prison protocols in which unskilled executioners administer drugs of unknown origin.
"The problems are all across the board," he said. "It's not just one thing. A big problem now is the lack of transparency about the source of the drugs and the quality and the potency of the drugs."
Deborah Denno, law professor at Fordham Law School and a death penalty opponent, also cited secrecy concerns.
"It makes it more troubling for the next execution," Denno said, "because we can't even learn from the botches."