A report shows a patient died after being prescribed with a powerful painkiller which doctors previously told him not to take.
A GP has been blamed for the decision to give Voltaren to the man, who died in 2012 after suffering from kidney and other organ failure.
An inquiry found the doctor failed to fully check the patient's medical history by not asking him enough questions or reviewing his medical notes.
The man had previously had a bad reaction to the drug and a warning had been put on his clinical file about five years earlier by another doctor.
The GP who was investigated said he did not recall the patient had ever suffered "renal impairment", possibly due to diclofenac - the medical name for Voltaren.
A report into the 80-year-old's care also revealed the patient did not know Voltaren and diclofenac were the same thing.
The case was investigated by Health and Disability Commissioner Anthony Hill after a complaint was made by the man's wife.
It has also been noted the man's earlier adverse reaction to the drug may not have come up on the doctor's computer due to a merger between the medical centre and another practice.
From pain to rapid decline in health
The man, who had a complicated medical history, visited his GP in 2012 with ongoing ankle pain, which could not be managed with ibuprofen.
The doctor gave him a two-week supply of Voltaren and suggested the patient go back to the surgery in a month for tests.
He did indeed return to the surgery, this time with pain in the joints of his right foot.
A diagnosis of probable gout was made and the man was told to keep taking Voltaren.
Just two days later, the pensioner was back at the clinic complaining that he was unable to empty his bladder.
Checks revealed the man had "urinary retention" and he was taken to hospital.
There, he was found to have had low blood pressure; he was also vomiting and later suffered a heart attack. He was also diagnosed with "acute on chronic renal failure".
He was moved to the intensive care unit (ICU), where his organs continued to fail.
With a poor prognosis and the patient's condition deteriorating, his family and clinicians made the decision to take him out of ICU. Treatment was stopped and he died in hospital.
In his report, Mr Hill said: "When prescribing medication to a patient, a doctor must ensure they are familiar with the patient's medical history, in order to accurately asses the patient's needs and to satisfy themselves that the medication will be in the patient's best interests.
"Failing to do so can have serious and potentially fatal consequences for the patient."
He told Checkpoint it was not possible to tell if it was the Voltaren that killed the patient, as he was also on other drugs that had the potential to impact on renal performance.
The Medical Council has been urged to consider whether the GP is fit to continuing practising.
The doctor was ordered to write an apology to the man's wife and do more training on the best approach to prescribing drugs.
In his report, Mr Hill declined to name the medical centre or give its location.
Medical mistakes - not for the first time in an inquiry by the Health and Disability Commissioner - were also linked to administration.
In this case, the man's file stated: "Diclofenac sodium - renal failure/retention - avoid".
According to the GP, that warning didn't flash up during the consultation time with the man.
The medical centre has been criticised for "not ensuring that its computer systems were fully functioning, or that a temporary system was in place for its doctors to follow, while the systems were undergoing changes".
The centre has been told to do an audit of its clinical records to ensure no other critical patient drug alerts were missed during the merger of its surgeries.