A plan to give seriously ill Australians faster access to potentially life-saving drugs could be delayed because of Prime Minister Malcolm Turnbull's decision to cancel a week of lower house sittings.

The government has promised to introduce a fast track for drug approvals that would give patients access to promising new prescription medicines up to two years earlier than under the current system.

The new "provisional pathway" system is due to begin on January 1 next year - but that timetable depends on Parliament's approval.

And with Prime Minister Malcolm Turnbull controversially cancelling a week of the House of Representatives, the draft laws now appear unlikely to pass through both chambers before Parliament rises for its two-month summer break.