A Kentucky judge says the state must either switch to a single drug to perform executions within 90 days or prepare to go to trial in a lawsuit challenging the state's three-drug method of carrying out capital punishment.

Franklin Circuit Judge Phillip Shepherd ruled Wednesday that the state's three-drug method may no longer be necessary now that other states have successfully used a single drug to execute condemned inmates.

The ruling comes about 20 months after Shepherd halted all executions in Kentucky. He imposed the ban after inmates challenged the three-drug method.

At least five states have switched to a one-drug execution method. Three states _ Ohio, Washington and Arizona _ have conducted single-drug lethal injections. Arizona put an inmate to death Wednesday using only pentobarbital.