A 75-year-old woman died after a Lakes District Health Board doctor gave her two drugs that should not be used together.
An investigation by Health and Disability Commissioner Anthony Hill slammed the doctor for the "medical error" and found the DHB in breach for failing to have a "safety-net" plan in place to check and challenge prescribing if needed.
The woman, who has not been named for privacy reasons, was rushed to hospital in 2016 with suspected pulmonary embolism (PE) - a condition in which one or more arteries in the lungs become blocked by a blood clot.
That day, she was given a drug called enoxaparin to prevent blood clots. Three days later, after she was confirmed to have PE, she was given another blood thinner drug called dabigatran, in addition to enoxaparin.
Either medicine can be used to treat PE, but they should not be administered together.
As a result she suffered a haemorrhage and was quickly rushed to the intensive care unit where her condition deteriorated.
The doctor at fault told the family that the "potential medication error" may have contributed to the woman's death. He apologised to the family and the woman died a short time after that.
While Hill was critical that the doctor prescribed the drugs together when they shouldn't have, his investigation identified a more widespread lack of clarity around their use at the time.
"The pharmacy review is an important safety-net to check, and sometimes challenge, prescribing," Hill said.
He found that in addition to the medication error there were other issues with the use of existing DHB tools and policies.
The woman deteriorated during her stay at the hospital and, had the DHB's communication tool been used, it is likely that the woman's care would have been escalated sooner, Hill said.
The commissioner said the way in which the error was disclosed to the family was not ideal. He was critical of both the content of the DHB's open disclosure policy, and communication of the policy to staff.
The DHB were told to make a number of changes to improve its policies, guidelines, and documentation to ensure better safe-netting if errors do happen.
Hill also told the DHB to apologise to the family.