A decision is looming on whether thousands of Australians with multiple sclerosis will continue getting subsidised access to two life-changing drugs.

The medications, which go by the brand names Ocrevus and Kesimpta, are listed on the Pharmaceutical Benefits Scheme but are up for review at a meeting this week, where the government is pushing for a substantial price cut.

Without government support, Ocrevus could cost patients as much as $33,000 a year.

Roche Australia, which makes the drug, has blamed the "archaic" way in which PBS medications are priced and is threatening to pull its product from the scheme if the government goes ahead with its plans.

But the two drugs needed to remain on the PBS, which caps prices at $25 for general patients and $7 for concession card holders, Health Minister Mark Butler said.

"I want to be very clear about the difference that they are making to many Australians living with MS, and I want to make sure that drug continues to be available for them at PBS prices," he told reporters in Burnie on Wednesday.

The stoush stems from the way drugs on the PBS are priced: they are grouped into categories, with the cheapest drug in the group acting as a benchmark.

The listing of a substantially cheaper competitor drug, Briumivi, could force a 40 to 50 per cent price cut for Ocrevus and Kesimpta, AAP understands.

The committee responsible for PBS listings is meeting until Friday to discuss the best course forward.

MS Australia, which advocates for people with the disease, said it was encouraged by Mr Butler's comments.

"I welcome his emphatic support for Ocrevus and Kesimpta and the Minister's strong desire to see this matter resolved in a manner that ensures these life-saving medications remain available on the PBS," chief executive Rohan Greenland said.

Mr Butler also blamed policy changes in the US, which is now linking domestic drug prices to those in comparable countries, making medicine companies in Australia more reluctant to accept a price cut.