A federal judge ruled Wednesday that Tennessee's new lethal injection procedures are cruel and unusual punishment, interrupting plans to execute a death-row inmate next week.

The protocol "presents a substantial risk of unnecessary pain" and violates inmate Edward Jerome Harbison's constitutional protections, U.S. District Judge Aleta Trauger said.

The new protocol, released in April, does not ensure that inmates are properly anesthetized before the lethal injection is administered, Trauger said, which could "result in a terrifying, excruciating death."

A spokeswoman for the state attorney general's office said officials are reviewing the ruling and have not decided whether to appeal. Tennessee Governor Phil Bredesen's office had no immediate comment.

The ruling comes as several lawsuits have been filed in various states challenging the constitutionality of lethal injection as an execution method. Lethal injection has been adopted by 37 U.S. states as a cheaper and more humane alternative to electrocution, gas chambers and other execution methods. But at least eleven states have suspended the use of lethal injection while they evaluate the procedure.

Harbison was scheduled to be executed early next Wednesday for beating an elderly woman to death during a burglary in 1983.

Trauger did not issue a stay or throw out the death sentence for Harbison, who has lost all his appeals. He can be legally executed once the state adopts a valid method of execution, she said.

Kent Scheidegger, legal director for the Criminal Justice Legal Foundation, a nonprofit group that supports the death penalty, said the 6th Circuit Court of Appeals might reverse Trauger's ruling.

"They have been fairly hostile to these sorts of claims," Scheidegger said.

Another federal judge in Nashville earlier this year ordered a delay in the execution of convicted killer Philip Workman, citing the likelihood that the state's new guidelines could still cause unconstitutional pain and suffering.

But a three-judge panel of the 6th Circuit lifted that temporary restraining order, and Workman was executed by lethal injection May 9.

Bredesen, a Democrat, in February placed a 90-day moratorium on executions because of several glaring problems with the state's execution guidelines, including conflicting instructions that mixed lethal injection instructions with those for the electric chair. Tennessee was one of several states to re-examine its protocol.

George Little, State Department of Correction commissioner, adopted the new protocol despite having knowledge about the remaining risks of excessive pain for inmates, Trauger said. A spokeswoman for Little did not immediately return a message seeking comment.

Trauger said Little did not give enough consideration to a recommendation to discard the standard three-drug lethal injection cocktail in favor of a single drug method. Current training and medical expertise are not sufficient to ensure a painless executions, she said.

Most states use three drugs _ thiopental, an anesthetic; pancuronium bromide, a nerve blocker and muscle paralyzer; and potassium chloride, a drug to stop the heart. Each drug by itself is supposed to be capable of killing, but if not, the anesthetic is supposed to render the inmate unconscious while the other drugs do the job.

The debate over lethal injection came to a head last year in California when a federal judge ordered doctors to assist in the execution of Michael Morales, who was convicted of raping and murdering a teenage girl. Doctors refused, and legal arguments continue in the case.

The 8th U.S. Circuit Court of Appeals last month lifted a more than year-old stay on executions in Missouri, refusing to block capital punishment while a death-row inmate asks the U.S. Supreme Court to declare the state's form of lethal injection to be an unconstitutionally cruel punishment.

Tennessee executed last week convicted child killer Daryl Holton in its first electrocution since 1960.

Bredesen on Friday commuted a death sentence for Michael Joe Boyd because of "grossly inadequate" legal representation during post-conviction hearings. Boyd, who now goes by Mika'eel Abdullah Abdus-Samad, was convicted of murdering a man during an armed robbery in 1986. The death sentence was commuted to life without possibility of parole.