Background and Importance Pembrolizumab is a PD-1 antibody, which was first approved with a dosage regimen of 2 mg/kg every 3 weeks. In 2018, marketing authorisation was changed to fixed dosing of 200 mg every 3 weeks.

The Commission of Pharmacy and Therapeutics of our region has taken the stance that based on the available evidence both regimens may be used.

Therefore, our hospital has agreed on a protocol that establishes to use fixed-dose for patients with weight ≥ 100 kg and the weigh-based for < 100 kg.

Aim and Objectives Evaluation of the accordance to the protocol establish in our hospital for the dose of Pembrolizumab and to calculate the financial impact of this implementation.

Material and Methods Retrospective observational study in individuals who started pembrolizumab since 1August 2022 for 1 year.

Variables analysed were epidemiological, weigh, cancer type, initial date, fixed-dose or weight-dose protocol used, change of the protocol.

1081.75€ has selected as the vial price of 100 mg of pembrolizumab.

Data was extracted from our prescription software for chemotherapy (Oncofarm®).

Results 131 patients initiated pembrolizumab, 62.60% men, mean age 65 years old. Mean weight was 71.8 kg and four patients weighted >100 kg. Pembrolizumab cancer indications were: melanoma (6.11%), non-small-cell lung (57.25%), head and neck squamous (6.11%), renal (3.05%), colorectal (3.82%), triple-negative breast (9.92%), endometrial (5.34%), cervical (2.29%), gastric (2.29%) and others (3.82%).

74.05% (n=98) of the patients initiated at the fixed-dose and only 25.95% (n=33) with weigh-based dose. There were four patients with weight > 100 kg which initiated with 200 mg.

Of the patients that initiated with fixed-dose, 11.22% (n=11) changed to the weight-based dose. Dose was reduced in a mean of 24.91%, which implied a total cost reduction of 29012€ (mean 2637€ per patient) and represented a 14.86% mean cost reduction in comparison with continuing with the fixed-dose.

Conclusion and Relevance Although it was accorded to use weight-based strategy for the patients < 100 kg, the reality was than less than 26% of the new pembrolizumab treatments were in compliance with it.

However, it is true that approximately 10% of the patients were changed to the weight-based regimen in order to decrease the economical cost.

References and/or Acknowledgements Keytruda: EPAR – Product information.

Conflict of Interest No conflict of interest.