A Tennessee woman is charged with trying to kill her four-month-old baby with overdoses of sodium by administering a salt solution into his feeding tube while the infant was hospitalized.

Amber Brewington, 21, was arrested at Children's Hospital of Pittsburgh Wednesday morning after a hospital staff member alerted authorities that they had seen Brewington tampering with the baby's feeding tube late Tuesday evening.

Police found a syringe, a can of Pedialyte, and a canister of salt in her backpack. Police told The Pittsburgh Channel that the young mother confessed to doctors that she had poisoned her child.

The baby was admitted to University Medical Center in Nashville earlier this month with a mysterious illness. He was transferred to The Children's Hospital of Pittsburgh on July 9, where his condition improved slightly on the days his father was with him. The infant's condition worsened on the days his mother was present.

Authorities are not certain about how the sodium was administered to the child while he was still in Tennessee.

Brewington is charged with attempted homicide, aggravated assault and endangering the welfare of a child.

Pittsburgh Police Cmdr. Thomas Stangrecki told the local CBS news affiliate that no charges have been made against the father. He said it is unclear whether the couple is married, but they have two children together. Brewington also has third child by another man.