The Government says a select committee inquiry into Pharmac's drug-buying processes would take longer than current reviews of the agency.
The Opposition tried and failed to launch an investigation by the Health Select Committee earlier this week, after complaints it's taking too long to fund groundbreaking new cancer drugs.
Cancer patient Claudine Johnstone told The AM Show on Thursday she's leaving for Australia - where drugs like Ibrance are funded - to give her a chance of seeing her four-year-old daughter start school.
"Australia gives me the chance to see a glimpse of what my child will be as an adult. I won't get to be there as an adult, but I want a glimpse."
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Ibrance costs about $6000 a month. It's approved for use in New Zealand, but not yet subsidised by drug-buying agency Pharmac.
"The Pharmac process generally works very well," National MP Judith Collins told The AM Show on Friday.
"But we have, over the years, had a big increase in the number of drugs Pharmac can fund, and they decide which drugs they're funding from the money they've got."
She backs an inquiry by the Health Select Committee. The four National MPs on the committee voted in favour, but the three Labour MPs and NZ First MP voted against it. Tied 4-4, the motion - led by Nationals' Michael Woodhouse - failed.
"If there is actually a good reason to fund these drugs - like, they really do work - then that would be the opportunity for that to come out," said Collins. "And the other thing is if there are better drugs that we don't know about, then that would have come out too."
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Labour MP Iain Lees-Galloway, appearing alongside Collins on The AM Show, said the Government was already looking into Pharmac.
"Minister of Health David Clark is looking at how Pharmac funds new drugs, because that's an issue that's come up in the past. In came up when Judith's party was in Government as well. There wasn't a select committee inquiry [then].
"He's also looking into the transparency around decision-making, so the Government is taking action. It would be a lot slower if it was a select committee inquiry. The select committee can't actually instruct the Government to do anything, but it would take time looking into this."
Pharmac uses its size and buying power to keep the costs of drugs down. Lees-Galloway said despite the gaps in coverage, overall the system works well.
"New Zealand's survival rates for breast cancer are better than the OECD average - 87.5 percent of women with breast cancer make it to five years. That's better than most other countries," he said.
In Australia it's 89.5 percent, according to the latest OECD data.
But even with a budget close to $1 billion, Pharmac can't buy everything Kiwis need - or want.
"Of course we would like everybody to be able to get access to all the drugs they need but we have that Pharmac model in place so that we take the politicians out of this decision-making, that we have the experts making these decisions so that we can get more drugs available to more New Zealanders, so that more people are better off."
Collins agreed the Pharmac model largely works, admitting she was no expert.
"Sometimes people think that drugs will cure them or help them, and sometimes that's wrong," said Collins. "I just think we need to find out. I'm pleased to hear that David Clark is looking at this."
Pharmac is presently reviewing its processes and developing an early access scheme. Labour MP Louisa Wall, who is on the committee, said it would be inappropriate for it to hold an inquiry as Pharmac is one of its primary advisers.
"The fact we don't think the Health Select Committee is independent means that we will advise the House that we think either the Law Commission should undertake a review, or that Treasury should undertake a review with a specific focus on an early-access scheme, and provide options to the Government on how we can better serve people with cancer."
Like Collins, Wall said politicians aren't medical experts.
"The entity that makes those decisions is Pharmac. We will not intervene."