Two nurses have been criticised by the Health and Disability Commissioner after a three year old boy was given an overdose of codeine.

An anaesthetist prescribed 8.5 milligrams for the boy to have prior to getting his tonsils out at a private hospital.

Before administering the drug, a registered nurse asked a senior nurse to check the prescription - with both reading the prescription for codeine as 85 milligrams.

The recommended adult dose for codeine is between 30 and 60 milligrams.

They both discussed the large dose but didn't check with the anaesthetist - so the drug was given to the boy.

The mistake was realised when they checked the prescription for the boy's four year old sister who was to undergo the same surgery after him.