The mother of a Melbourne woman who was killed by her partner while he was having a drug-induced psychotic episode has broken down in court calling the murderer a "bastard" and "mongrel" as he was sentenced to 18 years in prison.

Key points: Daniel Eckersley wept in court as he was sentenced over the killing of his wife in July 2018

Daniel Eckersley wept in court as he was sentenced over the killing of his wife in July 2018 He had been overusing the drug tramadol which led to a psychotic breakdown, the court was told

He had been overusing the drug tramadol which led to a psychotic breakdown, the court was told The judge said this meant his moral culpability was "significantly reduced"

Daniel Eckersley used a 120-millimetre kitchen knife to kill the mother of his three children, Amanda Harris, in their Cranbourne North home in July 2018.

In sentencing, Justice John Champion called the murder "horrific" and said the "brutal killing" was witnessed by their children.

"You have destroyed your own family. Amanda Harris was a loving mother and partner, and innocent," he said.

But Justice Champion said there were also mitigating factors that "significantly reduced" the murderer's "moral culpability".

During the plea hearing in 2019, the court heard that Eckersley was suffering from a medication-induced psychosis at the time of the killing and believed Ms Harris was trying to poison him.

Amanda Harris was found by a neighbour who noticed smoke coming from the house. ( Facebook: Amanda Harris )

Rare side effect of tramadol a mitigating factor

Two of the couple's young children saw Eckersley smashing items in the kitchen with a hammer before he attacked Ms Harris, and one of the children tried to stop the fight.

Eckersley also tried to burn down the house as he fled the scene with his children.

The former baker was using a mixture of medication, drugs and alcohol to deal with a workplace injury and the court heard from medical experts that the overuse of tramadol caused his psychotic breakdown.

Tramadol was prescribed to the 40-year-old by a GP and the court heard that most doctors were not aware of its possible psychological effects.

Justice Champion said the side effects were "rare, but recognised".

Ms Harris had been in a relationship with Eckersley for 17 years and her parents were in court for the sentencing.

Her mother Christine Harris openly wept during the 90-minute proceedings but shouted in anger when the sentence was delivered.

The maximum sentence for murder is life, and the average sentence is 25 years in prison.

Eckersley also wept during the sentencing.

He will be eligible for parole in 14 years.

Justice Champion said he would forward his findings to the coroner's office to examine whether GPs should be made more aware about the rare side effects of tramadol.