A four-year-old boy with hay fever who was accidentally given an anti-psychotic drug had to be rushed to hospital after suffering what appeared to be a severe allergic reaction.

According to a report just released by the Health and Disability Commissioner, the boy had been prescribed liquid loratadine for hay-fever by his GP in January 2020 - but it was not until nearly two years later that it was opened and given to him by his parents in November 2021.

About half an hour after being given the medicine a second time, the boy experienced "an apparent severe allergic reaction" and had to be hospitalised.

Subsequent tests revealed the liquid loratadine also contained an anti-psychotic medication, haloperidol.

Symptoms of a haloperidol overdose include severe difficulty breathing, dizziness, loss of consciousness and uncontrollable muscle jerking and stiffness.

The pharmacy told the HDC it was unable to explain how the error happened.

It said the hay-fever medicine, loratadine, was supplied in 120ml bottles, so in order to fill the child's prescription for 200ml, the pharmacy had to put it into a new bottle.

Its records show the last time it had dispensed liquid haloperidol was five days before it prepared the boy's medicine.

A cylindrical flask was used to dispense this type of liquid medication, and the standard practice was to wash the flask immediately after use.

"It is unlikely that the flask would not have been washed for five days," the pharmacy told the HDC investigators.

It had also checked its stock levels against dispensing records but could find no error there.

"We regret that we are not able to locate a definite reason for this occurrence and are at a loss as to how this event could have happened."

The Health and Disability Commissioner, Dr Vanessa Caldwell, found the pharmacy had breached the patient's rights.

"The pharmacy has an organisational responsibility to provide a reasonable standard of care to its consumers. In my opinion, the error represents a failure by the pharmacy to provide services with reasonable care and skill."

However, she commended it on the actions taken once it became aware of the incident, including informing the boy's parents that the incident had occurred and that the pharmacy was investigating it, apologising to the family, and making an incident notification.

The drug safety agency Medsafe has also carried out an investigation into the incident.

That investigation concluded "the most likely scenario" was the inadvertent addition of haloperidol into the loratadine dispensing bottle (to make up a total of 200ml).

The pharmacy has since changed its process to require two people to check a medication during preparation and dispensing.

Other changes included acquiring a tablet counting machine and a blister packaging machine to ensure more accurate dispensing.

This had freed up technicians and pharmacists to focus on other tasks, such as dispensing and checking, the HDC report found.

"The pharmacy also increased staffing levels and implemented new processes to ensure staff members are aware of any brand changes and changes to medication positioning."

Dr Caldwell has also asked the pharmacy to do an audit of a random sample of 20 liquid medications requiring transfer to a dispensing bottle, to determine whether these were checked by two people, and report back with its findings.

-RNZ.