LAS VEGAS — A sedative that Nevada prison officials plan to use next week for the first lethal injection in the state since 2006 has been blamed for problems during executions in recent years in several other states.

The U.S. Supreme Court ruled in 2015 that the drug, midazolam, can be used in lethal injections. But the American Civil Liberties Union of Nevada pointed Thursday to Arizona's decision to stop using it following an execution that took nearly two hours to kill Joseph Rudolph Wood a year earlier.

"Midazolam has a terrible track record," ACLU spokesman Wesley Juhl said, referring to a drug that observers have seen leaving inmates apparently struggling to breathe before they are pronounced dead. The ACLU characterizes the plan for Scott Raymond Dozier's lethal injection next week less humane than putting down a pet.

"Midazolam has been implicated in seriously botched and observably troublesome executions in at least five states," said Robert Dunham, executive director of the nonprofit Death Penalty Information Center in Washington, D.C. He named Alabama, Arkansas, Arizona, Florida and Ohio.

"While Nevada may hope that it works, the frequency with which it fails could mean Scott Dozier is conscious and aware when the fentanyl starts to kill him and the paralytic is administered," Dunham said. "He could be aware of being suffocated to death."

Nevada Department of Corrections spokeswoman Brooke Santina did not immediately respond to questions about the execution plan made public Tuesday for Dozier's lethal injection next Wednesday at Ely State Prison, 250 miles (400 kilometers) north of Las Vegas.

The protocol calls for midazolam injections to be followed by high doses of two other drugs never before used in executions — fentanyl, the powerful synthetic opioid blamed for overdoses nationwide, then the muscle paralyzing drug cisatracurium.

Use of the third drug was rejected by a state court judge last November, postponing Dozier's execution amid concerns that rendering him immobile could "mask" or prevent witnesses from seeing signs of struggle or pain.

Dozier, 47, a twice-convicted murderer who has been on death row since 2007, has waived appeals of his case and said repeatedly that he wants to die. He also said he doesn't really care if he suffers. Critics call his request a bid for state-assisted suicide.

The Nevada Supreme Court in May overturned the postponement on procedural grounds but did not rule on the constitutionality of the lethal injection method.

The execution plan was revised last month to substitute midazolam for expired prison stocks of diazepam, a sedative commonly known as Valium that the state previously slated for first-ever use as a lethal injection drug.

Nevada, like many of the 31 states with capital punishment, has had difficulty obtaining execution drugs after manufacturers began refusing to allow their products to be used in lethal injections. The state now plans to join several others using midazolam as an alternative.

Juhl, of the ACLU, cited the July 2014 execution in Arizona in which an Associated Press reporter watched Wood snort loudly while his belly inflated and deflated after he had been administered midazolam and the potent painkiller hydromorphone.

Just six months before, Ohio was the first state to use midazolam in the same two-drug combination with hydromorphone. In that case, an AP reporter watched inmate Dennis McGuire gasp and snort after apparently becoming unconscious, with his stomach rising and falling and his mouth opening and shutting for 16 minutes of the 26 minutes before he was pronounced dead.

Juhl said the ACLU believes the paralytic was included in the Dozier execution regimen in Nevada to prevent witnesses from seeing if Dozier suffers a "torturous death."

The organization is asking a judge in Carson City to force prison officials to disclose records including where and when the lethal injection drugs were obtained.

The court filing did not seek to delay the execution, but ACLU lawyer Amy Rose said the public deserves to know how the state plans to put a person to death.