WASHINGTON — A Calvert County, Maryland woman was arrested Saturday following the methadone overdose of her 1-year-old grandson, police said.

The boy had been rushed to the hospital on Thursday when his mother feared he had been poisoned.

On Friday, after the Maryland Department of Child Protective Services contacted the Calvert County Sheriff’s Office, police learned that the infant had been with his grandmother at her Lusby home before going to the hospital.

A short time after the mother picked the 1-year-old up from the grandmother, he appeared lethargic and had symptoms of being poisoned. She immediately took the boy to the emergency room.

Medical staff at Calvert Memorial Hospital treated the infant with several doses of Naloxone — a drug that blocks or reverses the effects of opioids.

After being transferred to Georgetown University Medical Center, staff there determined the boy had suffered a methadone overdose. He was treated extensively, monitored and listed as critical/acute.

The infant’s grandmother has been charged with child abuse in the first degree, assault in the first degree and distribution of a controlled substance. She was arrested without incident.