A cost comparison of pembrolizumab: Fixed and weight-based dosing

Background Pembrolizumab, an immune checkpoint inhibitor, indicated to treat multiple cancers, was initially approved in Australia as weight-based dosing at 2 mg/kg every 3 weeks (Q3W). Subsequent approvals used ‘fixed’ dosages of 200 mg Q3W or 400 mg every 6 weeks (Q6W). Pharmacokinetic equivalence was demonstrated between dosing strategies, with no significant differences in efficacy or toxicity. Fixed dosing regimens are routinely used in Australia. Aim To model and compare the cost of weight-based dosing of pembrolizumab to standard fixed dosing regimens. Method A single centre, retrospective review was conducted. Patients, identified from dispensing software, who commenced on pembrolizumab between January and December 2022 were included. Patient demographic and treatment data was extracted from electronic medical records. Costs of weight-based doses were calculated and compared to the cost of fixed dosing. Variables such as acquisition cost, funding mechanisms and ‘vial sharing’ were considered. Results Fifty-two patients were included (63% male, median age 68 years). Of the 211 doses of pembrolizumab administered (average 4. 1 doses/patient), 161 were Q3W doses, and 50 were Q6W doses. The acquisition cost for a fixed 200 mg and 400 mg dose was 7646, and 15, 292, respectively. The average patient weight was 77. 6 kg (SD 19 kg), which equated to 5933 for a weight-based Q3W dose, and 11, 867 for the Q6W dose; a potential cost avoidance of 1965 and 3930 per dose, respectively. This represented a possible 23. 5% avoidance in medication acquisition cost. Over the study period of 1 year, using weight-based dosing for pembrolizumab had the potential to reduce medication expenditure by 467, 996. Discussion Significant cost avoidance could be achieved via weight-based pembrolizumab dosing. Given the substantial total cost of pembrolizumab, the growing number of indications and the expected equivalent treatment outcomes with weight-based pembrolizumab, the potential cost reductions of weight-based pembrolizumab at both institution and government level should be further explored.