Children's Commissioner Andrew Becroft is warning Pharmac not to play one group of children with a life-threatening illness off against another.
His comments come after RNZ revealed that Pharmac is likely to end the blanket provision of child cancer drugs.
Pharmac says it has long viewed the special exemption for child cancer drugs as "inconsistent" but it was jolted into finally addressing the issue in response to a discrimination claim taken under the Human Rights Act.
Patient advocate Fiona Tolich took a discrimination claim, asking why Pharmac was funding all child cancer drugs but would not fund Spinraza for about 35 children with spinal muscular atrophy, a deadly genetic condition.
Patient Voice Aotearoa chair Malcolm Mulholland said he was appalled at Pharmac's action.
"I felt physically ill. I just could not believe that Pharmac is going to go down this road."
Pharmac said no final decisions had been made but the most likely outcome of its review would be to bring child cancer drugs into the normal Pharmac process.
Mulholland said this was no way to address the issue raised in Tolich's discrimination claim.
"It's clear that Pharmac believes in order to address some inequity, you actually have to take something away from a group of people that are currently receiving it. Obviously, that's the game plan."
Pharmac stressed that no current medicine used by child cancer patients would be taken away, but Mullholland was worried about what would happen in the future - both for patients who were diagnosed after Pharmac changed the rules and for new drugs that came on the market.
"The road that Pharmac are pursuing will mean that there are most definitely [fewer] treatment options available for kids with cancer once they have been diagnosed."
Pharmac chief executive Sarah Fitt said any impacts were likely to be minor although she could not rule out a decrease in access to paediatric oncology drugs in the future.
"That may well be the outcome. But that is not our intent. We may leave it exactly as it is but we need to actually do the work and talk to the people involved and not preempt any decision."
Children's Commissioner Judge Andrew Beecroft called Fitt today to express his concern.
"I don't want a situation to descend into playing one illness off against the other. And children, with their illnesses, being bargaining chips when they're facing life-threatening conditions," he told RNZ.
"All children in New Zealand, surely, can have access to lifesaving treatment. That must be the starting point."
Health Minister Andrew Little said he would not want to see long waits for new child cancer drugs but he believed the government's review of Pharmac should address that issue.
"There have been too many cases where there has been a lengthy delay between an application for funding of a drug and putting it on the schedule ... we needed to change that, which is why we have the review under way."
RNZ repeatedly asked whether he agreed that Pharmac was likely to do away with the special exemption for child cancer drugs but he would not answer.
"I want the best for everybody, including children, actually, and especially children," he said.
ACT Party deputy leader Brooke van Velden said she was "alarmed" at Pharmac's move on child cancer drugs and it highlighted how stretched its budget was.
"We had the ability to review Pharmac and ask whether its funding was fit for purpose for the 21st Century and the government expressly forbade the Pharmac review from looking into whether we should reconsider funding."