JACKSONVILLE, Fla. -

A 28-year-old mother has been arrested in the death of her 6-month-old daughter.

Jennifer Frazier is facing charges of aggravated manslaughter with culpable negligence after her daughter, Javey Patterson, died in their Dellwood Avenue home in Murray Hill on June 30.

Detectives said Frazier admitted to mixing ibuprofen and antibiotics to treat her daughter's fever. She said she mixed the medicine in the same container and syringe she mixes her prescription methadone, a highly controlled narcotic pain reliever.

Frazier told detectives she gave her child the medicine about 7:45 p.m. June 29, and about 10 a.m. the next day, she found her baby dead.

Police said the medical examiner found no ibuprofen in the baby's system. Instead, he found a deadly dose of methadone, according to detectives.

Investigators said they don't know Frazier's intent, but regardless, they said the mother is at fault.

"She was the one who gave the child the medication," said Chief Tom Hackney, of the Jacksonville Sheriff's Office. "Her story is that she thought she was giving the child the ibuprofen. However, again like I said, there was no ibuprofen found in her system. The truth may never truly be known in this case. We've got an incident here that she stored her methadone in a box of her child's medication."

"Children don't have the metabolic pathways to break down methadone quite as easily as adults do," said Dr. Jay Schauben, of the Poison Control Center. "So they get into trouble with a lot less of a dosage than adults."

Schauben said cases like these should show how important it is to be beyond careful with any kind of medicine around children.

"You never know when there's going to be some sort physical interactions with the other," he said. "So clearly they should be administered individually, separately and maintained individually and separately."

Frazier is being held at the Duval County jail with bail set at $500,000.

Detectives said she does have other children, and the Florida Department of Children and Families is deciding what will happen with them.

Schauben said if Frazier took the baby for medical help immediately after giving her the medicine, the child would have likely survived.

He said if you ever have a question about medicine and children, call the Poison Control Center for free advice at 1-800-222-1222.