The state of Oklahoma has not carried out an execution since it botched the lethal injection of Clayton Lockett last year, an episode that drew heated worldwide criticism, sparked an investigation and prompted the state to revamp how it executes inmates.

On Thursday, the state plans to use its new execution protocol for the first time to carry out the first of four executions Oklahoma has scheduled over a seven-week period. Lawyers for these four inmates hoped to delay these executions, but a federal appeals court Monday denied their requests for a stay.

It has been more than eight months since the execution of Lockett, who was convicted of murder and numerous other charges. Lockett grimaced, clenched his jaw and writhed on the gurney before dying inside the Oklahoma State Penitentiary in McAlester on April 29. A state investigation released later found that the execution team failed to properly insert the needle to deliver the lethal injection drugs, a problem that was exacerbated when no one monitored the IV and compounded when no one involved knew what to do as the situation unfolded.

Lockett’s execution was actually scheduled to be the first of two that night in McAlester. Charles Warner was set to be the 112th person executed in Oklahoma by lethal injection, but his execution was postponed until after a review of the Lockett execution could be completed. The scheduling of two executions just two hours apart caused the warden and paramedic involved in Lockett’s lethal injection to feel additional stress and urgency, according to the state investigation.

Warner, who was convicted of raping and murdering his girlfriend’s 11-month old baby, is now scheduled to be executed Thursday. The Oklahoma Department of Corrections also has the executions of Richard Glossip, John Grant and Benjamin Cole, all convicted of murder, on the calendar between late January and early March.

These four inmates filed a request for a stay last week with the U.S. Court of Appeals for the 10th Circuit, arguing that Oklahoma’s planned lethal injections would make them suffer “burning and intense pain.” In particular, the request argues against the use of the drug midazolam, a sedative that has been involved in three problematic executions.

The appeals court denied this latest request Monday, rejecting the arguments that midazolam poses a risk to the inmates and that the inmates are being experimented upon. A federal district court had denied a similar request last month.

Dale Baich, one of the attorneys for the inmates, said in a statement that if the executions are carried out, “we may never know how much suffering occurs” due to Oklahoma’s use of a paralytic agent. He said the attorneys will next ask the U.S. Supreme Court to delay the executions.

Oklahoma’s new lethal injection policy, put into effect last September, hikes up the amount of midazolam that will be administered during executions going forward. For Lockett’s execution, 100 milligrams of midazolam were supposed to be injected; going forward, the state plans to use 500 milligrams of midazolam, the same amount used by Florida in executions.

This new lethal injection policy also states that five journalists would be allowed to witness executions going forward, down from the 12 media witnesses allowed to witness Locket’s execution and others. News organizations had filed a lawsuit in August arguing for greater media access to executions in the state, because key parts of Lockett’s execution and his death occurred outside the view of the reporters in attendance.

The execution of Lockett last year marked the first time Oklahoma used a three-drug combination that included midazolam, which is used to sedate surgery patients before they are anesthetized. (In 2013, Florida became the first state to use midazolam in an execution.)

Ohio announced last week that it would no longer use midazolam and the drug hydromorphone to execute inmates, a change that came nearly a year after that combination was used to execute an inmate who choked and gasped before dying. The state of Arizona used the same combination last year in an execution that lasted for nearly two hours as the inmate gasped and snorted.

These state opted to try new and largely untested drug combinations because of an ongoing shortage of lethal injection drugs. Lethal injection remains the main method of execution in the United States, but in recent years states that carry out executions have struggled to obtain the necessary drugs because European companies and officials have protested the use of drugs supplied by European companies in executions.

The executions of Lockett and Warner were set to occur in March of last year, but had to be pushed back because the state did not have the drugs it had previously used for executions.