Parents of child with Cystic Fibrosis have been fighting for Pharmac to make a revolutionary but very expensive drug available in NZ.

The parents of a 12-year-old boy who suffers from cystic fibrosis say a Labour victory is their only hope of getting life-changing drugs for their son.

Wayne and Kim Davidson discovered their son Tylah was born with the life-threatening genetic disease, and have searched for the drugs that could save his life ever since.

A few years ago they discovered Tylah had the specific gene mutation that a drug called Kalydeco targets, which Wayne Davidson described as akin to winning Lotto.

JOSEPH JOHNSON/STUFF Kim Davidson with her son Tylah Davidson,12, who has cystic fibrosis.

But Pharmac declined a funding application for Kalydeco from supplier Vertex in 2015 "based on the high cost and poor cost-effectiveness", director of operations Sarah Fitt said.

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The Davidsons considered going to Australia where the drug is publicly funded until they realised they would not be eligible as non-citizens.

JOSEPH JOHNSON/STUFF The Davidsons have been fighting for Pharmac to make a revolutionary but very expensive drug, Kalydeco, available for people like him in New Zealand. The drug would reverse the effects of cystic fibrosis for 4 per cent of cystic fibrosis sufferers who have a specific gene mutation like Tylah.

Now they hope a Labour Government will deliver on a pledge to set up a $20m fund for rare diseases over four years.

The party's health spokesman David Clark said medicines for rare diseases missed out on Pharmac funding under the existing criteria and the commitment was a starting point to address the gap.

Apart from a pilot for a contestable rare diseases fund in 2015 by Pharmac, the National Government had not supported separate resourcing model for medicines like Kalydeco.

STACY SQUIRES/STUFF Labour's David Clark says they will give $20m to plugging a funding gap for rare diseases.

National's Jonathan Coleman said: "Pharmac needs certainty about the benefits these drugs provide, the likelihood of delivering better health gains than other treatments, and that it's affordable."

The Davidsons say this leaves families like theirs with no hope.

"This is our child, and there is a drug available that effectively cures him... and doubles his life span and it's like... the elusive wonder drug, it is always going to be out of our reach because of Pharmac's stance," Kim Davidson said.

JOSEPH JOHNSON/STUFF Physio twice a day helps break up thick mucous in Tylah's lungs.

New Zealand Organisation for Rare Disorders (NORD) Collette Bromhead said the pilot fund was a "good start" but the decisions on funding were still made on value for money, rather than value for patients.

For now, the Davidsons continue with constant vigilance to protect their son from the ravages of the disease.

Daily use of a nebuliser, morning and night physiotherapy and religiously taking medications with food are critical to manage the build up of thick mucous in the lungs and the lack of enzymes in his pancreas.

The list price (un-negotiated) for Kalydeco is NZ$382,000 per patient per year.

"The scariest thing for us is his health will decline, not get better," Kim Davidson said.

People with cystic fibrosis battle the effects of a defective gene that creates thick mucous in the lungs and strips enzymes from the pancreas.

Kalydeco reverses the damaging effects in four per cent of cystic fibrosis patients.

SUPPLIED Collette Bromhead, chief executive of New Zealand Organisation for Rare Disorders (NZORD) and senior lecturer in molecular microbiology at the College of Health, Massey University, Wellington.

An estimated 36 people would benefit from the drug in New Zealand, which costs more than $382,000 per year.

The average life span for cystic fibrosis patients is 37 years with half dying by the age of 34.

A recent test showed Tylah's lung function had dropped to 60 per cent and increasing fatigue made it hard for him to keep up with school work and sports.

Cystic Fibrosis New Zealand (CFNZ) which represents patients like Tylah advised the Davidsons early this year they would be taking a step back from lobbying for Kalydeco.

Chief executive Jane Bollard said as a small charity, CFNZ lacked the "resources and information required to carry out a full lobbying campaign, at this point in time."

​The organisation fully supported public funding of Kalydeco but had decided to spend time gathering information and support from doctors to strengthen future lobbying work, Bollard said.

The change was "gutting" Kim Davidson said.

The couple say the high price of Kalydeco was hard to justify, but the onus was on the Government to ensure access for its citizens.

A spokesman for Vertex said the development of Kalydeco and another cystic fibrosis drug Orkambi required an investment of "billions of dollars" over more than a decade.

Kalydeco is publicly funded in many countries including Australia, England and Ireland.

"New Zealand is the last country worldwide with substantial eligible patients with no access to Kalydeco."

Kim Davidson said Pharmac's position sent a bad message to Kiwis.

"The fact that it is available in so many other countries, what is this showing New Zealanders about the Government's commitment to the health of its people."

WHAT IS CYSTIC FIBROSIS?

Cystic fibrosis is the most common life-threatening genetic disorder affecting Kiwis.

According to Cystic Fibrosis New Zealand, 500 Kiwis have the illness. One in every 5000 babies is born with the condition and diagnosed with a heel-prick test during newborn screening.

About one in 25 New Zealanders carry the gene and won't know this unless they meet someone else with the gene and have a baby.

It is a life-limiting and incredibly challenging disease which affects the person "every minute of every day in every way," a spokeswoman for CFNZ said.