One case was classified as abuse, three cases were minor exposures and did not require medical treatment; however the other nine were referred to hospital.
National Poisons Centre director Dr Adam Pomerleau said methadone poisonings were rare in New Zealand.
"Methadone is an opioid medication and like all other opioids, they all produce very similar effects on the body. The symptoms of opioid poisoning are pretty recognisable, they include coma, respiratory depression and small pupils."
Pomerleau said regardless of age, the effects of methadone can be reversed quickly and easily thanks to a drug called Naloxone.
"It's incredibly effective and every paramedic will carry it on them. Naloxone is an incredibly powerful antidote that can reverse the effects of the drug."
Pharmacy Council chairman Mark Bedford said it was uncertain what the next steps would be in terms of an investigation.
"When an issue like this happens it goes straight to the Health and Disability Commissioner and there's a really robust process around that," he said.
"It will be investigated by that office and then it may be referred to the pharmacy council which is the regulator of pharmacists.
"Until we go through that, or get that notification [and we are aware of it] we can't do anything else at this point. But it's been acknowledged and it's really difficult times for everybody."
Bedford said he was extremely saddened by the accident and said the situation was an unfortunate one.
"All our support and sympathy for the family. Being a parent and a grandparent, I know how difficult these times are."
A Hawke's Bay pharmacist who wished to remain anonymous said mixing up medication in pharmacies was not uncommon.
"Some of these mistakes are easy to make. You're working on the dispensary bench and you see the prescriptions and just think yes okay."
In terms of the methadone case in Hawke's Bay, the pharmacist said they believed the mistake would have been made when transferring the medication.
"It's just a guess, but I'm thinking the error must have been made during the transfer, someone must have picked it up and given them the wrong bottle."
The 1-month-old baby still remains in Hawke's Bay Hospital in a stable condition.
