SIOUX FALLS, S.D. (KELO) — A registered nurse pleaded not guilty to federal charges that she exchanged fentanyl for another substance while working as a nurse in Chamberlain.

Lisa Merrigan is accused of replacing two vials of fentanyl with another liquid on two dates in August and September of 2021.

Fentanyl is an opioid painkiller.

She is charged with two counts of tampering with a consumer product and two counts of obtaining a controlled substance by misrepresentation, fraud, forgery, deception and subterfuge.

Documents from the South Dakota Board of Nursing allege Merrigan engaged in unsafe practices, substandard care and unprofessional conduct when she switched out the fentanyl.

On Nov. 16, 2021, the nursing board suspended her license but stayed the suspense on the condition Merrigan successfully complete a Health Professional Assistance Program, according to a state board document.

The document said that if Merrigan violated the HPAP agreement her license would be immediately suspended.