Doses of methadone are prepared for distribution to patients at the Taipas rehabilitation clinic in Lisbon August 10, 2012. Reuters/Rafael Marchante

A five-year-old girl died on Sunday after what is being believed to be a methadone overdose. Her death comes five days after she was found unconscious and was subsequently transported to The Children’s Hospital at Westmead.

On Jan. 17, the little girl was found unconscious at her home in Quakers Hill. The alarm was raised by the grandfather of the child, who had fallen asleep while watching television. When he tried to wake her, she was unresponsive.

The paramedics treated her at the scene before taking her to the hospital. The girl had remained in critical condition upon her arrival at the hospital. The matter is being investigated by the Child Abuse Squad, AAP (via Yahoo News) reports. The parents are assisting the detectives in the investigation.

Upon conducting tests, methadone was discovered in the girl’s urine. “One examination (at hospital) has revealed the child had methadone in her urine,” Hawkesbury duty officer Inspector Peter Jenkins said, according to AAP (via Sky News). It is being assessed whether the overdose was accidental.

Methadone is largely used as a painkiller for those recovering from heroin addiction. Its composition is similar to heroin. The legal distribution of the chemical substance is very restricted. It can only be obtained at a pharmacy or clinic.

The National Centre for Biotechnology Information details the dangers presented by indigestion of methadone. If consumed by children, the centre notes, methadone “is potentially lethal even in a small dose (0.5 mg/kg). Amounts present in the home may be greater than that necessary to produce fatal toxicity in infants and children: therapeutic analgesic adult doses are 5 mg to 20 mg; doses for MMT programs are 50 mg to 120 mg.”

According to the Daily Telegraph, the girl’s parents were away at work. She was being taken care of by her grandfather.