Last-ditch motions for appeals and stays of execution are rushing through courts, many of them centering on the importation and use of sodium thiopental, The Arizona Republic reports.
Several states have bought the anesthetic from Britain because it is no longer available in the United States.
The U.S. Drug Enforcement Administration last week seized Georgia's sodium thiopental supply to verify whether it had been imported legally.
On Wednesday, attorneys for an Arizona killer whose appeals have run out released a letter from British authorities asserting 12 adverse patient reactions, many for ineffectiveness, to sodium thiopental from the same batches imported to carry out U.S. executions.
Eric King is scheduled for execution March 29 for murdering a store clerk and a guard during a robbery in Phoenix in 1989.
Daniel Cook is slated to die April 5 for torturing, sodomizing and killing two restaurant workers in Lake Havasu City in 1987.
The Arizona Supreme Court has been asked to set execution dates for two other inmates and will soon be asked for permission to execute a third, the Republic said.