OKLAHOMA CITY — Two Oklahoma death row inmates scheduled to be executed next month sued state corrections officials Wednesday for details about the drugs that will be used to execute them, including their source.Under state law, no one may disclose who provides Oklahoma with the three drugs it uses to execute condemned prisoners. Lawyers for Charles Warner and Clayton Lockett fear the men could suffer severe pain if Oklahoma is allowed to maintain a "veil of secrecy.""Plaintiffs have no means to determine the purity of the drug which may be used to execute them, and whether that drug is contaminated with either particulate foreign matter or a microbial biohazard that could lead to a severe allergic reaction upon injection," the lawyers wrote in their state court lawsuit.Lockett is scheduled to be executed March 20 for the 1999 shooting death of a 19-year-old Perry woman. Warner is set to be executed on March 27 for the 1997 death of his girlfriend's 11-month-old daughter. The men seek a restraining order that would halt their executions. A hearing on that will be held Tuesday before District Judge Patricia Parrish in Oklahoma City; clemency hearings set for this week and next week remained on the Parole and Pardon Board's schedule Wednesday. .Oklahoma shields its drug suppliers' identities to protect them from potential reprisal, Department of Corrections spokesman Jerry Massie said Wednesday. He said the agency was aware of the inmates' lawsuit but declined to comment. Diane Clay, director of communications for Oklahoma Attorney General Scott Pruitt, said the office had received the petition and is reviewing it."We can confirm that Oklahoma is in compliance with the law," Clay said.Oklahoma and other states that have the death penalty have been scrambling for substitute drugs for lethal injections after major drugmakers — many based in Europe with longtime opposition to the death penalty — stopped selling to prisons and corrections departments.Under previous protocol, inmates continuously received a sedative while paralytic drugs actually killed them. As supplies dried up, Oklahoma dropped its requirement that inmates receive a sedative continuously and began to shield what it would disclose."Thus, at the same time that defendants are turning to untested and untried execution methods, they are also shielding information about the execution methods from meaningful disclosure or scrutiny," the lawyers wrote. They also claim the executions should be stopped because the Department of Corrections purportedly changed the protocol without sufficient notice to the public.Lawyers for the Oklahoma inmates do not challenge the men's guilt or the use of lethal injection, just the state's policy of not disclosing how it intends to kill the two."If you don't know what they're using there's no way to know if it is cruel and unusual punishment," Susanna M. Gattoni, one of the lawyers representing Lockett and Warner, said in a telephone interview.They suggest that a Tulsa compounding pharmacy challenged by lawyers for a Missouri death row inmate who was executed early Wednesday may have supplied Oklahoma with its lethal drugs. The Apothecary Shoppe, in a deal with lawyers for Michael Taylor, agreed not to supply pentobarbital, a sedative, for Taylor's execution.They also say a veterinary medicine supplier may have provided the pentobarbital to the state; the drug is also used to euthanize animals.Warner and Lockett's lawyers said in their lawsuit that compounding pharmacies are not regulated by the U.S. Food and Drug Administration and that, as a result, there is a risk that the two Oklahoma inmates could suffer as they die.A spokeswoman for The Apothecary Shoppe didn't immediately return calls seeking comment.Compounding pharmacies, which custom-mix prescription drugs for doctors and patients, are generally overseen by state boards, although a law adopted last year allows larger compounding pharmacies to register with the FDA and submit to federal inspections.Gattoni and her colleagues say substandard pentobarbital could leave inmates fully conscious as drugs to paralyze them and stop their heart are administered."There will be at most only a few seconds for them to make any physical or verbal sign of distress before they are paralyzed," they wrote."Plaintiffs will experience extreme pain and suffering when the third drug — potassium chloride — is administered to stop their hearts, but their paralysis by vercuronium bromide will mask their suffering from witnesses."The lawyers say they believe Oklahoma used compounded pentobarbital as the first drug in a January execution. Michael Wilson's final words were, "I feel my whole body burning," and then he didn't move.