LITTLE ROCK, Ark. — The Arkansas Supreme Court on Wednesday issued a stay of execution for a condemned prisoner scheduled to die on Thursday, imposing a new curb on a plan that once called for the state to empty nearly a quarter of its death row by the end of the month.

Separately, in a decision that Arkansas officials immediately said they would appeal, a Circuit Court judge here in Pulaski County ruled that the state could not use one of its lethal injection drugs, vecuronium bromide, amid allegations that the prison system misled a pharmaceutical distributor.

Before Wednesday’s decisions, the courts had already compelled the state to abandon plans for three of the eight executions it hoped to carry out before the expiration of a different lethal injection drug, midazolam, at the end of the month. By sunset on Wednesday, about 24 hours before the state intended to execute Stacey E. Johnson and Ledell Lee at a prison southeast of Little Rock, it was unclear whether any executions would happen.

The Supreme Court’s stay applied only to Mr. Johnson, 47, who was sentenced to death in 1994 for the rape and murder of a woman in Sevier County, which is along the border with Texas. Lawyers for Mr. Johnson have insisted he is innocent and persuaded the justices to issue a stay of execution to allow for forensic tests.