OKLAHOMA CITY, Oklahoma - A federal judge says Oklahoma's lethal injection protocols are constitutional and that the state can proceed with the scheduled executions of four death row inmates early next year.

U.S. District Judge Stephen Friot on Monday ruled against a group of condemned inmates who say the state's use of the sedative midazolam in a three-drug method presents a risk of cruel and unusual punishment.

12/22/2014 Related Story: Judge To Rule On Oklahoma's Execution Method

They sued after the April 29 execution of Clayton Lockett, who writhed on the gurney, mumbled and lifted his head during his 43-minute execution that the state tried to halt before it was over.

12/16/2014 Related Story: 9 Investigates: Plaintiffs File Lawsuit Following Lockett Execution

The state has purchased new medical equipment, adopted new protocols and ordered more training, and prison officials say they're ready for the next execution on January 15.