For four months, a nurse at Fairview Southdale Hospital fed her drug addiction every day at work by stealing powerful painkillers from patients and sneaking in saline solution to cover up her crimes, according to federal charges filed Friday and state regulatory records.

Cali May Arndt, 32, of Cottage Grove, was charged in U.S. District Court in Minneapolis with obtaining a controlled substance by fraud while working at Fairview Southdale Hospital as a registered nurse. Arndt used syringes to remove morphine, hydromorphone and fentanyl from vials sitting in "secured automated medication dispensing systems," then replaced the drugs by injecting the vials with saline solution, according to the charges.

Arndt resigned from Fairview Southdale on Oct. 30, 2012, the day after an investigation into the thefts began, according to the Minnesota Board of Nursing, which suspended her license in February 2013.

The charges come as the Legislature considers bills that would tighten the state's oversight of drug-addicted nurses, whose theft of drugs and other misconduct can put patients at serious risk.

According to the Nursing Board's consent order, which Arndt signed in agreement with its findings:

Arndt admitted stealing the narcotics starting in June 2012 and continuing for more than four months. She said she had been treating her chronic back pain with Percocet and developed an addiction.

She said she stole from hospital patients during every shift she worked and sometimes more than once per shift, replacing the drugs with saline solution.

Arndt acknowledged that "some patients may not have received their prescribed doses of pain medication due to her actions," the board document read.

After two years, Arndt can petition the board to have her license reinstated and be able to show that she is successfully addressing her chemical dependency.

Cindy Fruitrail, a spokeswoman for Fairview Health Services, would not say how many patients may have been hurt by Arndt's actions.

Arndt and her attorney declined to comment on the allegations.

The number of reported drug thefts at Minnesota hospitals and nursing homes more than doubled from 2005 to 2011, according to a coalition of law enforcement and health officials convened after a series of alarming incidents.

Their report, released in 2012 and said to be the first of its kind, found 250 cases with prescription drugs stolen or reported missing at Minnesota health care facilities in the years reviewed.

Bills in the state House and Senate would require the Nursing Board to suspend nurses who fail a state drug and mental health monitoring program unless they can prove they are not at imminent risk of harm to the public.

The bills were introduced following a Star Tribune series last fall that reported how Minnesota nurses continued to practice despite histories of drug thefts and patient harm, criminal convictions or failed participation in state drug monitoring.

Staff writer Randy Furst contributed to this report.

Paul Walsh • 612-673-4482