A Medical Council inquiry has begun into allegations that a consultant medical oncologist at the Beacon Hospital in Dublin prescribed the wrong dose of chemotherapy to a woman for 16 days.
The patient, Sinéad Ní Dhúlaing-Johnson, had been a producer in RTÉ. She died in 2010.
The inquiry has heard that Ms Ní Dhúlaing-Johnson got the wrong higher dose for 16 days in August 2008 and became extremely unwell and required hospitalisation until November.
The dose was about twice what is recommended.
The inquiry has granted the consultant oncologist anonymity, following an application by the doctors' legal team. The doctor is being named only as 'Dr A'.
An application by the Beacon Hospital that its facility not be identified was not acceded to.
It is alleged Dr A is guilty of professional misconduct and or poor professional performance on four counts and that Dr A prescribed an incorrect higher dose of the drug Temozolomide and for an excessive duration.
It is also alleged Dr A failed to record this, or notify this to the patient and her husband Eddie Johnson and that Dr A failed to notify the other treating health professionals in a timely manner.
The inquiry has heard that Ms Ni Dhúlaing-Johnson developed a brain tumour in 2000 and had care in the US.
She had an operation in August 2003 and the recommendation was then for chemotherapy.
The tumour recurred in 2008 and an MRI scan showed it was inoperable.
It was recommended she receive treatment at the Beacon Hospital, which the inquiry has heard was the only centre performing a particular type of radiation treatment.
She was prescribed 350 milligrams of the chemotherapy drug, per day, instead of 150 milligrams.
The error was not recognised for 17 days, by which time she had been taking it for 16 days.
The inquiry has heard that Mr Johnson said he was only told of the chemotherapy overdose involving his wife on 19 September 2008 by Dr A.
Barrister Patrick Leonard, for the Medical Council chief executive, said the inquiry will also hear criticism of the timeliness of Dr A's notification on 22 September to the patient's referring GP, Dr David Lombard and consultant oncologist, Dr John Crown at St Vincent's Hospital.
Eileen Barrington, senior counsel for Dr A, said the consultant was a competent, well-qualified and highly regarded doctor.
She said Dr A admits to making a human error, in a patient who was suffering a malignant and terminal brain tumour.
Ms Barrington said there was no suggestion in the inquiry that the error caused, or hastened the patient's death.
Dr A discussed the error with the hospital pharmacist, treating colleagues and the medical director and CEO of the Beacon.
Ms Barrington said Dr A has repeatedly expressed regret at the error, which was the first in Dr A's professional career.
She said a personal injuries process was concluded with Ms Ní Dhúlaing-Johnson and her husband, with an admission in October 2010 and the patient had died two years after the error.
Ms Barrington said the dose was "excessive" but cannot be described as an overdose, given that the dose level of 350 milligrams can be given.
She said Dr A admits to prescribing an incorrect dose.
Dr A arranged a "root cause" investigation and a new oral chemotherapy prescribing process was introduced at the hospital by 19 September 2008.
