COLUMBUS, Ohio -- Four inmates overdosed in two days at the same Ohio prison earlier this year, requiring the use of CPR and doses of an anti-overdose drug as guards scrambled to revive the men, according to state prison records.

The “inmate was unresponsive, blue in the face and lips and did not have a pulse nor was he breathing,” according to a report on an overdose late in the evening of Feb. 18 at Pickaway Correctional Institution. The next night, an inmate was found “laying on the floor of bathroom with eyes closed, covered in vomit,” another report said.

The documents, obtained by the Associated Press through an open records request, don’t name the drugs the inmates used, but say guards administered the anti-overdose drug naloxone to revive them. Naloxone is typically used to revive people overdosing on opioids like prescription painkillers and heroin.

Ohio prison officials say multiple overdoses in such a short period at the same prison is unusual, but say the state’s opiate epidemic is also inside prison walls, which is why they keep the anti-overdose drug stocked.

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“Contraband does filter in. That’s why we have these tools,” said Stuart Hudson, the prison agency’s health care and fiscal managing director.

Overdoses behind bars have become an issue as the country’s painkiller and heroin epidemic has worsened, though the problem is more closely associated with jails. Earlier this month, seven female inmates overdosed at the Fayette County Jail in southwestern Ohio.

In New Hampshire, on a single weekend in January three inmates overdosed in the state prison for men in Concord and a fourth overdosed and died at a New Hampshire prison halfway house in Manchester. Officials used naloxone on two of the three inmates in the men’s prison.

Drug overdoses are among the leading causes of deaths in California state prisons, killing an average of 17 inmates each year, according to a 2016 report by a federal court-appointed receiver who oversees the system as a result of a long-running lawsuit over inmate health care.

An investigation is underway to figure out where the drugs came from that led to the overdoses at the Ohio prison 15 miles southwest of Columbus, said prisons spokeswoman JoEllen Smith. The Department of Rehabilitation and Correction takes the prevention and seizure of contraband seriously, she added.

Hudson said most offenders enter with some kind of substance abuse problem that follows them during their time behind bars. Illegal drugs enter the prisons via visitors and staff and other ways, such as being thrown over fences, he said.

The agency continues to boost treatment programs to address the issue. The state is also getting ready to test a system injecting inmates about to be released with a drug that blocks the craving for opiates.