An infant with a hole in his heart had his life put in danger after a pharmacy misread a prescription and gave him drugs 10 times stronger than they should have been.
His parents now face an anxious wait to see if their son has lasting brain damage and are about to lay a complaint with the Health and Disability Commissioner.
Ben Tuffin has called the ordeal a "nightmare" and is urging parents always to double-check their child's medication.
"I want to get the word out so other families know and take more precautions when it comes to scripts. Pharmacists need to check - when it's done by someone like that you put your trust in them."
On January 8, Tuffin and fiancee Nina Brickland welcomed Sydney Junior Tuffin into the world, but he was born with a hole in his heart.
The neonatal doctor at Middlemore prescribed 0.5ml a day of furosemide, a diuretic to keep the fluid off his lungs while he gained weight and grew strong enough for heart surgery. The parents went to a pharmacy not managed by the hospital to fill the script, then took their new son home. They thought they were doing everything right, administering the medicine once a day through Sydney's nasal tube and even had a home nurse visit daily.
But he kept losing weight.
The parents took him back to the hospital and Tuffin said the doctors and nurses instantly suspected what might be wrong.
Tests confirmed Sydney had very low sodium levels - a symptom of dehydration from an overdose of diuretics. Sydney had been given 5ml a day - 10 times the prescribed dose.
"Because he was on such a high dose, every bit of food or water, it was just sucking all of it out of him," Tuffin told the Herald on Sunday.
The doctor told him if they hadn't brought Sydney in, he would have suffered kidney damage. Because he spent a fortnight severely dehydrated, he could also have suffered brain damage, but they won't be able to tell for a few years.
The Herald on Sunday has seen the doctor's prescription, and the drugs dispensed by the pharmacy, which exposes the error.
Auckland University professor and neonatal paediatrician Jane Harding said furosemide could cause dehydration and kidney damage.
Although brain damage was possible, it was "extremely unlikely", she said.
Tuffin said he was furious at the pharmacy.
"We checked the script and the doctor got it right, it was the pharmacy that screwed it up ... they gave us full strength and they should have known straight away, because it was for a new-born baby.
"They were just careless.
"I wanted to go down to the pharmacy and have it out with the pharmacists but I kept my cool."
Tuffin said as soon as his son got the correct dosage, he started getting better. By the next day, he had gained 50 grams and after a further six days in the Kidz First unit, Sydney was discharged.
"If we actually had the correct dosage at the beginning, our baby would have been nice and strong and ready for surgery."
The pair intend laying a complaint about their ordeal with the Health and Disability Commissioner.
"I want them to be more on to it. If it's a new-born baby that's under six months and they're already sick, they need to be triple or quadruple checking these prescriptions."
The pharmacy involved did not respond to interview requests.
What is furosemide?
A diuretic that causes the kidneys to get rid of unneeded water and salt from the body into the urine.
• Correct dose: 0.5ml a day
• Dose given: 5ml a day