It is estimated that up to 500 case notes will have to be examined as part of a wider investigation into allegations made by nursing colleagues in Naas where the agency nurse worked between January and June of this year.
A complaint alleging she administered an intramuscular injection of the major tranquilliser, haloperidol, to a patient for whom it had not been prescribed led to the exhumation of the body of John Gethings in Co Wicklow on Friday.
However the nurse, who is Irish and in her 30s, has denied the allegation.
Mr Gethings's son, Thomas, has expressed a wish that the nurse be considered innocent until proven guilty.
In a statement yesterday, the Nurse on Call recruitment agency said the nurse under investigation had worked at Naas General Hospital and for "three other hospitals/clients" over short periods from November 2002 to January 2003.
"Since 21st January, 2003, she has worked solely at Naas Hospital. Prior to the recent allegations we did not receive any complaints regarding this nurse," the statement said.
It is understood that as well as working in the Naas hospital, the agency nurse was employed by two Dublin hospitals; one is a private institution and the other a large public hospital.
According to one source, up to 500 patient notes will be scrutinised as part of a wider examination of cases in which the nurse was involved.
The practice of nursing in the Republic is regulated by An Bord Altranais. It is believed the nursing board will meet this Wednesday to consider the matter.
It has the power to institute a fitness to practise investigation against any nurse registered in the State.
It can also seek a High Court order temporarily removing a nurse from its register pending completion of a full inquiry.
A fellow nurse is believed to have made a statement that an unprescribed major sedative was administered to "settle" a patient in Naas General Hospital who became agitated at night.
Night-time agitation is relatively common in older people during an acute illness or against a background of cognitive impairment.
Major tranquillisers have a much stronger sedative effect than minor tranquillisers such as Valium and sleeping tablets from the benzodiazepine group of drugs.
They are used in the treatment of psychosis, severe mental agitation and also have a role as anti-nausea drugs in certain clinical situations. If overdosed, major tranquillisers cause a depression in the respiratory centre in the brain, which controls regular breathing, leading to death.
Older people with cognitive impairment often become disturbed and upset at night.
Doctors must tread a fine line between dealing with the distress of the patient while not over-prescribing to the point where the patient becomes the victim of a "chemical cosh".
A post-mortem on Mr Gethings's body was carried out by the Assistant State Pathologist, Dr Marie Cassidy, on Friday.
Her examination will have included taking specimens from the liver and kidneys for toxicological testing.
These tests will establish the level of any drugs in the body at the time of death. Both the type and concentration of any drugs found will determine whether a criminal prosecution is warranted.