PITTSBURGH — A Tennessee woman pleaded guilty but mentally ill Monday to charges that she injected salt water into her infant son's feeding tube in an effort to poison him while he was at a Pittsburgh hospital.

Amber Brewington, 23, of Duck River, Tenn., will spend five to 15 years in a mental facility after pleading guilty to aggravated assault and endangering the welfare of a child in Allegheny County. Brewington entered the plea after prosecutors withdrew an attempted homicide charge against her.

"I didn't mean to hurt my son," Brewington told Common Pleas Judge Jeffrey Manning, though authorities believe she harmed the boy in an effort to generate sympathy for herself.

The boy is partially blind and suffers from mild cerebral palsy, epilepsy, autism, has water on the brain and has suffered a stroke. Authorities believe those ailments resulted from Brewington's actions, though she told police when she was arrested that she was just trying to speed up the death of her ill, suffering child, who was then 4 months old.

Manning ordered a mental competency hearing after Brewington's arrest in 2008. A nurse had caught her in the act at Children's Hospital of Pittsburgh, where Brewington's son, Noah King, was transferred after doctors in Tennessee tried to treat him.

A psychiatrist testified then that Brewington suffered from Munchausen by proxy syndrome, in which a caregiver tries to cause illness or injury to generate sympathy. Brewington also had borderline personality disorder and suicidal thoughts, the psychiatrist said.

A Tennessee couple is trying to adopt the boy.

Brewington's attorney, public defender Amy Lindberg, called her client "incredibly remorseful" and said she "really took complete responsibility" for her actions Monday.