A Melbourne man stabbed his partner to death in front of their young children was suffering a medication-induced psychosis and believed she was trying to poison him, a court has heard.

Key points: Daniel Eckersley murdered his partner, Amanda Harris, before setting fire to their family home

Daniel Eckersley murdered his partner, Amanda Harris, before setting fire to their family home The prosecution told a court Eckersley had displayed "controlling behaviours" during their 17-year relationship

The prosecution told a court Eckersley had displayed "controlling behaviours" during their 17-year relationship The defence said it was a "nasty example of domestic murder" but Eckersley believed Ms Harris was poisoning him

Daniel Eckersley, 39, used a kitchen knife to murder the mother of his children, Amanda Harris, in their Cranbourne North home in July 2018.

He then set fire to the property.

He grabbed the couple's children and put them in his car before fleeing the property to dispose of his clothing.

A neighbour noticed smoke coming from the house and dragged Ms Harris onto the patio as he waited for firefighters to arrive.

But the 36-year-old had already died from a stab wound to her chest.

Two of the couple's children witnessed the fatal assault after an argument between Ms Harris and Eckersley, who had been using a hammer to smash items in their kitchen after emptying the cupboards and fridge.

The court heard he was experiencing a medication-induced psychosis and deludedly believed Ms Harris was trying to poison him and that the kitchen was contaminated.

One of the children tried to grab Eckersley's hand to stop him stabbing his mother, the court heard.

Amanda Harris sought help from relatives and contacted Eckersley's sister on social media. ( Facebook: Amanda Harris )

Prosecutor Brendan Kissane QC said Eckersley had "exhibited various controlling behaviours" during his 17-year relationship with Ms Harris.

Mr Kissane said Eckersley had sought medical assistance for depression in the week before the murder and began taking anti-depressants on top of pain medication he had been abusing.

Eckersley's plea hearing in the Victorian Supreme Court heard Ms Harris had sought help from family members including Eckersley's estranged sister, who she contacted over social media days before her death.

"Your brother needs you, he's about to have a breakdown, his depression is really bad," Ms Harris wrote.

"Everything is getting to him."

The court heard that after murdering Ms Harris, Eckersley told a friend, "I think she was poisoning me and the kids … it's all got to do with these pills".

Defence barrister Tim Marsh told the court the case was a "nasty example of domestic murder", but that Eckersley was suffering delusions at the time caused by a pain medication he had been prescribed 18 months earlier.

"He believed, vividly believed, that he was being poisoned by Ms Harris," Mr Marsh said.

Psychiatrist Andrew Carroll, who was engaged by the defence, said Eckersley's psychosis was caused by an extremely rare reaction to the prescription drug Tramadol, which he had been taking in much higher dosages than prescribed.

Ms Harris' sister, Louise Flynn, told the court she felt cheated and angry that she never got to say goodbye to her sister, whose death was "unbearable".

"How could the one person who was meant to love her and be a role model to her children take her life away?" Ms Flynn asked.

"I just don't understand it."

The hearing before Justice John Champion continues.