There is "no evidence" that an overdose of medication given to a seriously unwell baby by nursing staff contributed to his death after a heart transplant, a coroner has ruled.
Charlie Douthwaite was given 10 times as much of the drug cyclosporine as he had been prescribed to stop his body rejecting the transplanted heart, an inquest heard.
The mistake was discovered by ward sister Judith Gray on the Freeman Hospital 's Paediatric Intensive Care Unit (PICU), but coroner Karen Dilks said there was no evidence it "caused or contributed" to his death more than two months later.
Charlie's story was in 2017 when he was the smallest baby in the EU who needed a donor organ.
The inquest heard Charlie, from Fenham in Newcastle, faced a struggle from survival from day one after being born with hypoplastic left heart syndrome - a condition that would lead to death within a few days without medical intervention.
He had his first open heart surgery at just three days old, and a number of procedures culminating in a heart transplant in November 2017.
But his organs continued to fail and his condition deteriorated until he eventually lost his fight on March 27 last year, aged just five months.
Freeman Hospital consultants Mohamed Nassar and Margarita Guillen Ortega described Charlie's "stormy" experience in intensive care.
Dr Guillen Ortega said: "Charlie was never stable without extraordinary help.
"He had a devastating circulatory failure because stress after stress became overwhelming.
"It was an incredibly intense and prolonged ICU experience and it shows how children are so incredibly resilient. I don't think any adult would have been able to be so sick for so long.
"I don't think in comparison to that [the drug overdose] would be contributory to his death."
Sister Judith Gray told the hearing that she discovered on December 8 that Charlie had been given 15 milligrammes of immunosuppression drug cyclosporine - 10 times what he had been prescribed.
She said: "I can only assume there was some doubt when they saw what this dose meant on a syringe, because it's not a dose you could successfully administer from our oral syringes.
"Charlie subsequently had doses of that size - it's not something that would start alarm bells ringing
"The consultant apologised and said we believed an error in administration had resulted in Charlie receiving too much of the drug - at that time it was 10 times what he should have had.
"As a result of this we now have to document the volume and the dose of the drug that's given."
Pathologist Dr Srinivas Annavarapu said the cause of death was "multi-organ failure due to fibrosis and renal failure as a consequence of hypoplastic left heart syndrome".
Coroner Karen Dilks recorded a conclusion that Charlie's death was due to natural causes.
She said: "Charlie Douthwaite suffered from hypoplastic left heart syndrome - a condition not compatible with life.
"He underwent multiple surgical procedures to prolong his life, including a heart transplant.
"Immunosuppression medication was prescribed to reduce the risk of rejection of the transplanted heart.
"On December 8 he was administered a higher than prescribed dose for an indeterminate period of time. There's no evidence this caused or contributed to his death.
"The underlying cause is clearly a natural condition which he couldn't survive had he not had medical intervention."
Following the inquest Charlie's mum Tracie Wright said she had been left with unanswered questions.
She said: "There are still a few grey areas and a lot of questions they couldn't answer, like how long the overdosing had been going on for."
But Tracie added: "We're just going to concentrate on keeping his memory alive and promoting organ donation."
Since Charlie's death Tracie and Steven Douthwaite have raised thousands for the Freeman Hospital where Charlie was treated and set up a charity in his name "to give children something to look forward to in hospital".
A Newcastle Hospitals spokesperson said: "We once again want to express our sincere condolences to all of Charlie’s family for their loss after his brave battle. His death had an impact on all of our staff who cared for him at Newcastle Hospitals.”
