"She was dead scared of Trimethoprim, because she knew it would kill her," said Mr Richardson, 83.
Mrs Richardson was first given Trimethoprim, a bacteriostatic antibiotic, to treat a urinary tract infection in 2005.
She soon developed a bad reaction and was quickly taken off it.
But a year later, she was administered it again and developed a shocking reaction.
Flushing red itches became ballooning blisters that engulfed her body and caused her to lose 50 per cent of her skin.
She was hospitalised for 15 days with toxic epidermal necrolysis - a rare, life- threatening skin condition caused by a reaction to the Trimethoprim.
In October 2013, Mrs Richardson tripped and fell at her home in Halswell, Christchurch. She broke her hip and had a pin inserted at Christchurch Hospital.
A few days later, she was sent to Princess Margaret Hospital across the city to recuperate. While recovering, she picked up a urinary tract infection.
Hospital staff then administered Trimethoprim - despite the MedicAlert bracelet warnings.
"I got a call from the hospital at 2am, saying they were taking her into the burns unit because she had come out in blisters all over," Mr Richardson recalled, becoming emotional at the thought of his wife's painful death two years ago.
"If she knew they were going to give her Trimethoprim, she would've been screaming her head off, out of her wits. And if they told me, I would've been looking for someone to punch, after all the warnings we had had."
Blisters "the size of my hands" covered her body and had to be "scrubbed off" in an operating theatre, Mr Richardson said.
"She screamed when the nurses came to turn her in her bed. She was in complete agony."
Within days of scrubbing, she had lost 65 per cent of her skin.
Terrified and weak, she died in her beloved husband's arms on November 30, 2013. Throughout her ordeal, she had been wearing her MedicAlert bracelet, which stated "Allergy Trimethoprim".
Her medical notes had bright-coloured stickers highlighting her allergy.
"It's not so much that she died, it's the way she died that gets me," Mr Richardson said. "It was an agonising and needless death that should never have happened."
Canterbury DHB told NZME. News Service it was "sorry for the tragic events" that led to Mrs Richardson's death.
It offered to meet Mr Richardson, who declined, saying: "I don't know if I could speak civilly with them."
CDHB chief executive David Meates confirmed that a serious adverse event inquiry has now been completed.
But he refused to comment further as the death was still subject to both a coronial inquest and Health and Disability Commissioner complaint.
"This office continues to keep the complainants informed about progress on their complaint," a spokeswoman for the commissioner said.
Documents seen by NZME. News Service show CDHB's review last year led to recommendations that it strengthen processes for displaying past adverse reactions at point of care.
It also recommended reviewing its "prescribing environment to reduce interruptions" and to "identify and manage workloads".
Mr Richardson hopes his wife's death helps reduce the risk of such an event happening in the future.
"I know nothing can bring Eunice back but any improvements to the system would be most welcome," he said.
MedicAlert NZ is lobbying Parliament to implement new national health and safety protocols dedicated to Mrs Richardson's memory.
"Eunice's death appears to have been entirely avoidable," MedicAlert New Zealand chief executive Murray Lord said.
"The concern is that this issue of not correctly utilising MedicAlert bracelets is far wider than we actually realise."
