Weight-based pembrolizumab gives more bang for the public buck

3 minute read

Fixed dose regimes of the life-saving immunotherapy have advantages, but cost isn’t one of them.

Administering pembrolizumab according to patient weight could save tens of thousands of dollars per patients, an Australian study finds.

Pembrolizumab is a PD-1 inhibitor used in Australia to treat cancers including melanoma, non-small cell lung cancer, Hodgkin’s lymphoma, deficient mismatch repair colorectal cancer and urothelial cancer.

The drug was first approved for use at a weight-based dose but moved to fixed dose regimens at the request of the manufacturer. These are convenient, use all contents of the vial, and lower the risk of error, but they ultimately cost the PBS more, the authors say. Returning to weight-based dosing saves money with no loss of efficacy.

A single centre study was conducted in Melbourne looking at 52 patients, weighing an average of 77.6kg each, median age 68, 64% male. They received, collectively, 211 doses of pembrolizumab from January to December 2022 (160 of them 200mg every three weeks and 51 of them 400mg every six weeks).

During this period, a fixed dose of 200mg for three weeks cost $7646, and a 400mg dose for six weeks cost $15,292.

The cost of acquiring a weight-based dose of 2mg/kg every three weeks would have been $5933, and for 4mg/kg every six weeks it would have been $11,867.

Weight-based dosing would have provided a saving of 23.5%.

“Over the study period of one year, using weight-based dosing for pembrolizumab had the potential to reduce medication expenditure by $467,996,” the authors write.

More would be saved if weight-based doses were capped at 200mg and 400mg, they say.

“The above modelling is based upon strategies involving waste minimisation, where the unused remainder of the vial is reserved and used for the next patient’s dose, with the assumption of no wastage or loss occurring,” the authors write.

Other countries are looking at returning to weight-based dosing and a recent US study found that doing so for PD-L1 positive advanced lung cancer treatment alone could save $USD82.5 million a year.

“This represented an annual cost saving of 24% without any known compromise in efficacy or outcomes and could also potentially be extended to indications other than lung cancer,” the American study found.

Switching to weight-based dosing would require procuring smaller vials (50mg), which were previously available in Australia but were discontinued. Alternatively, the savings could be achieved through vial sharing, depending on the number of doses being administered and the ability to use the vials before they reached their expiry date.

Vial banding, where people in a weight range are given set doses, has been adopted in some Australian hospitals. Capping doses at 200mg for three weeks or 600mg for six weeks for people weighing 100kg or more would also prevent amounts administered in excess of need.

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