Mike Graczyk, Associated Press
In this March 16, 2011 photo, Texas death row inmate Cleve Foster talks on a phone at the Polunsky Unit of the Texas Department of Criminal Justice outside Livingston, Texas. Foster, scheduled for execution April 5, 2011, was sent to death row for the murder of Nyaneur Pal, 30, a Sudanese refugee he met in a bar. He would be the first condemned prisoner in Texas to receive lethal injection using pentobarbital, which is being substituted as one the three drugs Texas uses for capital punishment. The switch is needed because of a nationwide shortage of sodium thiopental, the previous sedative drug used for nearly three decades in the country's most active death penalty state.

HUNTSVILLE, Texas — A condemned inmate moved one step closer to being the first person to be executed with Texas' new drug cocktail after the Texas Board of Pardons and Paroles on Monday refused a petition to convert his sentence to life in prison.

Cleve Foster, 47, is scheduled to die Tuesday evening for the slaying of a Sudanese woman abducted and shot after she met Foster and another man at a Fort Worth bar nine years ago.

Foster would be the third Texas prisoner executed this year, but the first to die since the state switched from using sodium thiopental to pentobarbital in its lethal three-drug mixture. The switch resulted from a nationwide shortage of sodium thiopental. Texas is the nation's busiest death penalty state.

Foster's lawyers went to a state appeals court Monday to challenge the drug switch. They also asked Gov. Rick Perry to use his authority to issue a one-time 30-day reprieve "to fully litigate and resolve questions" about the substitution.

Foster's attorneys claim Texas Department of Criminal Justice officials didn't follow administrative procedures properly when they announced the drug change last month. A state district judge rejected that argument last week, leading to Monday's appeal.

The drug swap is the most significant change in the execution procedure in Texas since the state switched from the electric chair to lethal injection when it resumed carrying out capital punishment in 1982. Pentobarbital, a sedative used in surgery and to euthanize animals, already is used in executions in Ohio and Oklahoma.

"The timing of the decision and disclosure raises serious concerns about the haste with which TDCJ seeks to implement this new process, and a lack of transparency by state officials," attorney Maurie Levin, a law professor at the University of Texas, wrote in a letter to Perry. ""We are not asking for a commutation or pardon, but for a reprieve of limited duration to permit these matters to be sorted in a careful and judicious fashion befitting of the task at hand."

Foster, a former Army recruiter, and his roommate Sheldon Ward were sentenced to death for the murder of Nyaneur Pal, 30, whose body was found in a Tarrant County ditch on Valentine's Day 2002.

The two men also were charged but never tried for the shooting death of Rachel Urnosky, 22, at her Fort Worth apartment in December 2001.

Foster blamed Pal's death on Ward, one of his recruits. Prosecutors, however, said evidence showed Foster actively participated in the woman's death, that he offered no credible explanations and lied and gave contradictory stories about his sexual activities with the victim.

Ward died of cancer last year while awaiting execution.

Foster grew up in Henderson, Ky., spent nearly two decades in the Army and was promoted to sergeant first class. Records showed court martial proceedings were started against him after he was accused of giving alcohol to underage students and having sex with an underage potential recruit. He was denied re-enlistment and had been out only a short time when Pal and Urnosky were killed.