(AP) — Arkansas has a new supply of a lethal injection drug that expired earlier this year, a prison spokesman said Monday, clearing the way for four double executions that will put eight men to death next month.

Arkansas Department of Correction spokesman Solomon Graves said the state has 100 vials of potassium chloride, one of three drugs used in the state’s lethal injection protocol. The state’s previous supply of the drug had expired in January.

“Coupled with the two remaining drugs, there are enough to carry out the scheduled executions,” he said.

Graves said the latest supply of the drug was received March 8 and expires at the end of August 2018. He did not say who provided the state with its new supply, citing an Arkansas law that keeps the source of its lethal injection drugs secret. Graves also did not say how much the potassium chloride cost and declined to release redacted photos of the drugs’ labels, which The Associated Press had previously used to identify the source of another Arkansas execution drug.

The state hasn’t executed an inmate since 2005, but Gov. Asa Hutchinson last month scheduled the eight executions to occur before another drug, midazolam, expires at the end of April.

“The governor has always maintained confidence in the ADC’s ability to procure the expired drug needed,” Hutchinson spokesman J.R. Davis said.

The state’s supply of vecuronium bromide expires on March 1, 2018. Graves said the state hasn’t replaced its supply of the other drugs.

Hutchinson scheduled the executions days after the U.S. Supreme Court said it wouldn’t review a state court ruling upholding Arkansas’ lethal injection law. The state Supreme Court earlier this month rejected an effort by the inmates to block the executions, saying there was no stay in place preventing the men from being put to death.

Attorneys for the inmates have asked a Pulaski County circuit judge to find the state’s lethal injection law and the three-drug protocol unconstitutional. An attorney for the inmates said they still believe the state should provide the information on the drugs.

“We’re still taking the position that they need to provide this information as to where it came from, who manufactured it, who sold it, etc.,” Jeff Rosenzweig said. “We haven’t yet been successful in that but we’re still trying.”

Under Arkansas’ protocol, midazolam is used to sedate the inmate, vecuronium bromide then stops the inmate’s breathing and potassium chloride stops the heart. The inmates’ lawyers fear the midazolam isn’t powerful enough to mask the pain caused by the other two drugs.

Since the U.S. Supreme Court reinstated the death penalty in 1976, only Texas has put eight people to death in a month — doing it twice in 1997. Arkansas has had multiple executions in the past, including triple executions in 1994 and 1997. At the time, the state Correction Department said multiple executions reduced stress on prison staff.

But the 2014 botched execution in Oklahoma of Clayton Lockett was the first of a scheduled double execution. Lockett’s execution was halted by the state’s prison director after Lockett writhed and groaned on the gurney. He died 43 minutes after the drugs began to flow.

An Oklahoma review team later recommended that at least seven days pass between each execution. The report said a veteran paramedic who placed Lockett’s intravenous line had noted a sense of urgency in the air.

The state announced it received a new supply of the vecuronium bromide in July, days after its previous supply of the drug expired. The drug appears to have been made by a subsidiary of Pfizer, even though the pharmaceutical giant has said it doesn’t want its drugs to be used in executions.

Using a redacted photo obtained from the Department of Correction, The Associated Press in July matched the new supply of the drug to labels submitted to the National Institutes of Health by Hospira, Inc., which Pfizer bought in 2015.