Background and importance Pembrolizumab is a humanised monoclonal antibody targeting PD-1 approved by the European Medicines Agency (EMA) in 2015. Currently, it has approval for several indications and is widely used.

Aim and objectives To calculate the budget impact difference of administering pembrolizumab at a personalised weight dose of 2 mg/kg every 3 weeks (Q3W) or 4 mg/kg every 6 weeks (Q6W) instead of a fixed dose of 200 mg (Q3W) or 400 mg (Q6W) in any indication since the new dosing strategy was applied in our hospital.

Material and methods Retrospective, observational, descriptive study of all the patients treated with pembrolizumab in all indications between July 2020 and June 2021. Collected variables: sex, weight, milligrams administered, number of cycles, vials used. The cost per milligram and per cycle of pembrolizumab was evaluated and the cost for two treatment strategies was calculated: cycles of 2 mg/kg (Q3W) or 4 mg/kg (Q6W) versus 200 mg (Q3W) or 400 mg (Q6W). All dispensations were transformed to cycles of Q3W for calculations.

Results Seventy-five patients (52 men and 23 women) were included with 16 different pathologies, the majority being non-small cell lung cancer (65.3%, n=49). The mean body weight was 72±13 kg (only two patients weighed 100 kg). The average cycles Q3W administered per patient was 8.3±6.9 and the average dose prescribed was 145±26 mg. The cost was €1 272 068 for the weight-based dosing and it would be €1 757 000 for the fixed dosin, which means an increased cost of 38%. Vials saved with the weight-based dosing were 347, which equates to a €487 743 cost saving in 1 year. The average additional milligrams and cost per cycle per patient with a flat dose was 55.1 mg and €773. A decreased dose compared with the fixed dose that was administered in 98.7% of patients (n=75), assuming economic savings related to these patients.

Conclusion and relevance Pembrolizumab fixed dose presents practical benefits in terms of prescription and preparation, but also an extra cost regarding our patients’ population in all indications, where only two patients weighed 100 kg. Weight-based dosing significantly reduces the cost of pembrolizumab and it is a good option in the era of personalised medicine.

Conflict of interest No conflict of interest