A Tennessee woman has been charged with attempted homicide for trying to poison her 4-month-old son at a city hospital by injecting a salt water solution into his feeding tube, police said.

They did not release the name of the boy, who remained in critical condition with sodium poisoning at Children’s Hospital of Pittsburgh on Wednesday. The boy’s 21-year-old mother, Amber Brewington, was taken into custody late Tuesday following the latest alleged poisoning attempt, police Cmdr. Thomas Stangrecki said.

The boy became ill and was taken earlier this month to Vanderbilt University Medical Center in Nashville, where he was diagnosed with sodium poisoning, Stangrecki said. The baby was transferred to the Pittsburgh hospital on July 9, he said.

During that time, the boy’s father traveled with him and his condition began to improve, Stangrecki said.

But the boy’s condition declined after his mother visited him on Sunday and again on Tuesday night, leading to Brewington’s arrest, Stangrecki said. She gave investigators a statement he could not describe, he said.

Brewington was found with a syringe, a container of salt and the children’s drink product Pedialyte, Stangrecki said. Police believe Brewington was using the syringe to inject the solution into the child’s feeding tube.

Investigators believe the boy had also been poisoned in Tennessee, Stangrecki said.

“We believe last night was another attempt to deliver more salt water or sodium to her child,” Stangrecki said Wednesday.

Brewington was also charged with aggravated assault and endangering the welfare of a child. She was awaiting arraignment in Pittsburgh on Wednesday.

It was not immediately clear if she would have an attorney representing her at the hearing.

The boy’s father was questioned, but is not suspected of wrongdoing and faces no charges, Stangrecki said.

Stangrecki said he’s not sure if Brewington is married to the child’s father. Brewington has two children with him and a third child by another man, Stangrecki said.

It was unclear who currently has custody of Brewington’s other children.