SEATTLE -- Seattle Children's hospital has apologized for a medical mistake that led to the death of a 15-year-old autistic boy last March.

Michael Blankenship, of Kent, was discharged on March 9 after having dental work at the hospital. He was found dead in his bed the next morning.

His death was caused by a drug overdose from a fentanyl pain patch normally used for patients with chronic pain, the medical examiner's office said.

At a news conference Tuesday, hospital officials said they are taking steps to make sure such a mistake never happens again.

"We can never bring back this child or fully understand to what level we have devastated their family," said Dr. David Fisher, Seattle Children's Medical Director. "We are deeply sorry for the family and will everything in our power to ensure this never happens to another child at Children's."

Fisher said the mistake wasn't the fault of any one individual, but rather of a process of checks and double checks that failed at multiple points.

According to the Food and Drug Administration, fentanyl should only be prescribed to patients who regularly take narcotic pain medication. It's not to be used to treat mild pain after surgery.

"We believe that the drug should not have been prescribed in the first place, and certainly not at the highest dosage," said Chris Davis, the Blankenship family's lawyer.

Davis has filed a wrongful death suit, alleging that two dentists and Seattle Children's were negligent and reckless in prescribing the drug.