"There is no evidence that Ms Dalley was adversely affected by the medication, either while in hospital or on her discharge home," Ms na Nagara said.
"Significantly, she appeared to respond well to the change in pain medication, and this must have been considered a breakthrough given the nearly four-week-long admission to hospital, during which clinicians struggled to identify the source of the pain and to treat it effectively.
"It is my view that Ms Dalley's death is not attributable to any shortcomings in her treatment or management."
Toxicology analysis showed levels of the prescribed drugs consistent with therapeutic use.
The toxicologist noted that methadone is a central nervous system depressant and that concurrent use of other central nervous system depressant drugs, such as amitiriptyline, cyclizine, olanzapine and quetiapine, may enhance its toxicity.
Ms Dalley had a significant medical history and had been admitted to Wanganui Hospital on April 7, 2012, complaining of acute onset of abdominal pain.
In a summary of four weeks' duration, a consultant surgeon reported that the source of pain was not able to be established, and it was clear there were frequent investigations made with a view to understanding the underlying pathology.
Ms na Nagara found that various medications were trialled to manage the pain. Ms Dalley was reviewed by the hospital pain team and discharged under their care.
Dr Michael Miller, specialist anaesthetist with a special interest in pain management, was asked to see Ms Dalley on May 1. He started Ms Dalley on 5mg of methadone, twice a day.
As methadone takes some time to build up to adequate levels, for three days Dr Miller kept Ms Dalley on the pethidine and morphine she was already receiving before weaning her off them. He also started Ms Dalley on gabapentin, as he felt it would further improve her pain control and allow doctors to wean Ms Dalley off the pethidine and morphine.
Ms Dalley saw Dr Miller on May 3 at the Pain Clinic and he noted she was looking much brighter and smiled. She told him the pain was under much better control but still troublesome. Dr Miller decided to wean Ms Dalley off the morphine and pethidine completely, and increased the methadone.
However, Ms Dalley's partner raised a concern that she had been prescribed various medications with central nervous system depressant effects. She also felt Ms Dalley had not been adequately observed on the new medication regime prior to discharge.
The olanzapine and quetiapine had been prescribed by psychiatrists in view of Ms Dalley's psychiatric history.
Ms na Nagara said she appreciated Ms Dalley's partner might have questions about her medical management and the post mortem findings.
She said she was assisted by the clinicians' comprehensive reports. Dr Miller had said he was aware of the risks and had rationalised the regime to the extent he considered possible.
The Chronicle was unable to contact Ms Dalley's partner for comment.
