The government's drug-buying agency Pharmac is planning to switch the breast cancer treatment Herceptin to a cheaper equivalent, and widen access to include stomach cancer patients.
Patient advocates have described the move as long overdue, and claim an earlier switch could have freed up cash for other vital medicines.
Pharmac chief medical officer Dr David Hughes said consultation on the proposal opened on Thursday, with stomach cancer patients set to get treatment from December.
"Pharmac has funded the biologic brand of trastuzumab (branded as Herceptin) since 2005 for the treatment of breast cancer, with approximately 900 people using the medicine last year," he said.
"Biologics are among the most expensive medicines that Pharmac funds, with the cost of trastuzumab in the top five gross medicines costs in 2021 and 2022.
"Transitioning from Herceptin to biosimilar Herzuma would release significant funds for Pharmac to invest in other medicines for the benefit of New Zealanders, including widening access to trastuzumab to New Zealanders with stomach (gastric) cancer.
"This is the Pharmac model in action - where we maximise our fixed budget, to negotiate savings and increase access to medicines."
Herzuma already has MedSafe approval, and has been used in New Zealand private hospitals since 2019 and in Australia since 2018.
Pharmac would maintain a supply of Herceptin for any patients who experienced problems with the new brand, Dr Hughes said.
The Breast Cancer Aotearoa Coalition - an umbrella group representing more than 30 groups - said it was confident the switch would have "minimal effects" on patients, given Herzuma's proven history.
Its chair, Libby Burgress, said however they were puzzled why it took Pharmac so long, given the constraints on the medicines budget.
"An earlier switch could have seen other vital medicines funded over the last three or four years" she said.
"We're also deeply disappointed that Pharmac hasn't extended access to cover those who need retreatment with this drug in advanced breast cancer.
"This is recommended in both the European and New Zealand Guidelines for advanced breast cancer and is provided as the normal standard of care in many other countries, including Australia."
The advocacy group continued to push for a rapidly injectable form of the drug, which would allow patients to get treatment closer to home and take the pressure off hospitals, she said.
"There are many other medicines for different breast cancer subtypes (hormone receptor positive and triple negative) that New Zealand women are missing out on, resulting in shorter lives for our women."