Ohio waded into uncharted territory Friday when it announced plans to switch from the usual three-drug cocktail used to execute inmates to a one-drug method that death penalty opponents praised as a step forward — albeit one that has apparently never been tried on prisoners.

The switch came two months after an Ohio inmate walked away from a botched execution attempt, and it is almost certain to get tied up in appeals and draw the close attention of other states that have long used the three-drug method.

"I chose to do it because I'm getting sued either way," Terry Collins, Ohio prisons director, said Friday.

Under the three-drug method, the first drug knocks out an inmate, the second paralyzes him and the third stops his heart — a process that death penalty opponents argue is excruciatingly painful if the first drug doesn't work.

The single-drug technique amounts to an overdose of anesthesia, Collins said.

Death penalty opponents hailed Collins' decision as making executions more humane but expressed reservations about using such an untested method. The same drug is commonly used to euthanize pets, to sedate surgery patients and in some parts of Europe has been used in assisted suicides.

"This is a significant step forward," said Ty Alper, associate director of the Death Penalty Clinic at the University of California, Berkeley, law school. "Paralyzing inmates before executing them — so we can't tell whether they are suffering — is a barbaric practice, and Ohio should be commended for stopping it."

Richard Dieter, director of the nonprofit Death Penalty Information Center, noted the new practice would essentially be an experiment performed on inmates.

"They're human subjects and they're not willingly part of this," Dieter said. "This is experimenting with the unknown, and that always raises concerns."

Ohio's decision, filed in papers Friday in U.S. District Court, said it would switch from a three-drug cocktail to a single injection of thiopental sodium into a vein. A separate two-drug muscle injection will be available as a backup.

Prison officials say that, although the techniques are new for executions, all three drugs are widely used in medical settings and their effects well understood.

With the change, Ohio also said it was ready to resume executions, on hold in the state since the unsuccessful attempt Sept. 15 to put to death Romell Broom, who raped and killed a 14-year-old girl in 1984.

Gov. Ted Strickland stopped the execution after two hours when executioners failed to find a suitable vein. Broom complained in an affidavit after the execution attempt that his executioners painfully hit muscle and bone during as many as 18 attempts to reach a vein.

The state said the new procedure will be in place by Nov. 30 in time to execute another inmate, Kenneth Biros, on Dec. 8. A federal judge had temporarily halted his execution because of the botched Broom execution but left open the possibility of the procedure taking place.

Temporary moratoriums are also in place in California and Maryland, where courts are reviewing proposed changes to injection procedures, though none involving a switch to a single drug.

Other states are unlikely to make a similar switch soon, said Doug Berman, an Ohio State University law professor and death penalty expert.

Several states have joined Ohio in facing constitutional challenges to their three-drug execution procedures, but Ohio is the first to drop that approach in favor of one dose.

The U.S. Supreme Court upheld the constitutionality of lethal injection last year, but Ohio's new system is substantially different from the three-drug process the court examined. In its ruling, Chief Justice John Roberts briefly addressed the prospect of using a single sedative in a dose large enough to cause death.

The one-drug method, Roberts said, "has problems of its own, and has never been tried by a single state."

That means Ohio could be opening itself to new litigation, said Deborah Denno, a law professor at Fordham University in New York and lethal injection expert.

"The inmates who are going to be executed could challenge the constitutionality of what's being raised in Ohio," Denno said Friday.

Collins said state officials consulted with an array of experts, including pharmacologists, pharmacists, coroners and anesthesiologist Mark Dershwitz, a University of Massachusetts professor and physician who advises state prison systems across the country.

The state said in a court filing last month it was having a hard time finding medical personnel willing to consult about injection because of professional and ethical rules.

The rules — which generally prohibit doctors, nurses and others from involvement in capital punishment — were deterring such personnel from speaking publicly or privately about alternatives to the state's lethal injection process.

Ohio has put 32 people to death since 1999, when executions resumed in the state.