JACKSONVILLE, Fla. -- A 37-year-old mother was arrested after her 1-month-old baby was rushed to the emergency room with a skull fracture on Monday afternoon.

Doctors at the pediatric intensive-care unit at Baptist Medical Center told police the baby boy was in full cardiac arrest.

After the staff revived the child, doctors found the infant was suffering from a skull fracture and there were traces of Methadone in his urine.

Victoria Klein was arrested that evening and booked into the Duval County jail. She was ordered held on $100,000 bond.

Klein told police she was the only person with the baby in the hours before he was transported to the hospital.

"The person who said they were the only one having any contact with the child has not been very cooperative in her interview, so, at this time, we are unknown how the child were able to come in contact with Methadone," said Melissa Bujeda, a spokeswoman for the Jacksonville Sheriff's Office.

The baby remained in critical condition on Wednesday morning.

Investigators were still looking into how the baby got Methadone -- a drug used given to people trying to overcome heroin addiction.

Klein's 19-year-old daughter told Channel 4's Laura Mazzeo that her mother and the baby were living at a rehab center and that's where the baby came in contact with Methadone.

The Food and Drug Administration label on Methadone advises nusing mothers not to use the drug because it can be passed through breast milk to a baby.

The Jacksonville Sheriff's Office and Florida Division of Children and Families were both investigating the incident.

Police said Klein has several previous arrests on drug charges and worthless checks.