Australia and the US appear headed for a test of wills to keep the Trans-Pacific Partnership 12-nation trade deal alive before US President Barack Obama leaves the White House in January.

Australia has been adamant patents for hi-tech biologic medications be exclusive for no more than eight years under the TPP.

The powerful US pharmaceutical industry and allies in US Congress, headed by Utah Republican and chairman of the Senate Finance Committee Orrin Hatch, have drawn a line in the sand demanding 12 years of exclusivity.

Last week the defiant Senator Hatch bluntly told reporters: "If Australia wants to be part of it, they have to meet our terms".

On Thursday the senator signalled his hardline approach had worked with the Obama administration set to bend to his demands.

"They said they'd satisfy me," Senator Hatch, who is waiting for the pledge in writing, told Inside US Trade.

The senator, buoyed by the discussions, predicted there could be enough votes in Congress to pass the TPP in the "lame-duck" period after the November 8 presidential elections and before January when Mr Obama's presidential term ends.

With presidential frontrunners Hillary Clinton and Donald Trump both opposing the TPP, the deal could die if Mr Obama fails to guide it through Congress.

Senator Hatch's belief the White House could alter the TPP agreement goes against a meeting of the 12 TPP nations - including the US, Australia, New Zealand, Canada and Japan - in Tokyo earlier this week.

Representatives from each nation, including top US negotiator Trade Representative Michael Froman, agreed they would not re-negotiate the deal.