TALLAHASSEE — Florida is switching to an untried drug for lethal injections, and death row lawyers are poised to fight the change, calling it a potential violation of the constitutional ban on cruel and unusual punishment.

Like many other states, Florida is running out of pentobarbital, a barbiturate and the first of three drugs injected into a condemned inmate in an execution.

The new drug is midazolam hydrochloride, a sedative that legal experts say has no track record of effectiveness on death row because it has never been used in an execution in the United States.

Legal experts say the question is whether it will make an inmate unconscious before two more powerful drugs take effect.

"No state has used that drug in an execution, so we don't know what's going to happen," said Richard Dieter of the Death Penalty Information Center in Washington. "The first drug is critical. If it doesn't work, the next two drugs are excruciatingly painful. Even when executing people, we need to respect dignity and humaneness."

Florida's lethal injection cocktail is administered in three intravenous stages and is intended to induce unconsciousness, paralysis and cardiac arrest. The second and third drugs are vecuronium bromide and potassium chloride.

Corrections Secretary Mike Crews said the state was forced to change the first drug because its supply of pentobarbital is low and the drug's maker prohibits its use in future executions.

"The reason was availability," Crews said.

Other states face similar challenges. Texas will get supplies of pentobarbital from a special pharmacy, and Ohio ran out of the drug after an execution last week.

Ohio and Kentucky list the new Florida drug as a default or backup drug, but neither state has used it in an execution.

Lawyers for Florida death row inmates want federal judges to review the new drug before it can be used.

In civil rights cases pending in U.S. District Court in Jacksonville, lawyers for death row inmate Etheria Jackson say the new drug "poses a substantial risk of serious harm and violates the evolving standards of decency encompassed in the Eighth Amendment," which prohibits cruel and unusual punishment. The change "warrants discovery, investigation and judicial review," they argued.

The lawyers say midazolam hydrochloride, marketed under the brand name Versed, "is the shortest-acting benzodiazepine on the market" and is primarily used as a sedative in a surgical setting before an anesthetic is used.

U.S. District Judges Timothy Corrigan and Marcia Morales Howard have scheduled oral arguments for Nov. 6.

The new drug cocktail will be used for the first time Oct. 15 in the execution of William Happ, who was convicted of the rape and strangulation of Angela Crowley of Fort Lauderdale. She was abducted from a pay phone outside a Crystal River convenience store in 1986 and her battered body was later found in the Cross-Florida Barge Canal.

She was 21 years old.

Happ, 51, told a judge in a 20-minute court hearing on Sept. 13 that he's ready to be executed and asked that no legal actions be taken to delay it.

"I've thought about this for many years," Happ said to Circuit Judge Richard Howard of Inverness. "I would prefer to have it carried out."

Happ's attorney, Eric Pinkard of St. Petersburg, declined to comment, saying the change in lethal injection procedures "is potentially subject to legal proceedings."

Deborah Denno, a law professor at Fordham University who has studied lethal injection procedures across the country, said Florida's continued use of a three-drug protocol is contrary to the trend in other states, which is to use one drug. She said the use of the new drug as an anesthetic poses a significant risk. Florida is one of 14 states that uses a three-drug cocktail, and one of 32 states with the death penalty.

"Florida is going against every trend we've seen in the last five years. In an effort to make this method of execution more humane, Florida seems to be regressing," Denno said.

Times staff writer Dan Sullivan and researcher Caryn Baird contributed to this report. Steve Bousquet can be reached at bousquet@tampabay.com or (850) 224-7263.