Projected lecanemab wastage from vial discard: Simulation based on Japanese interim post-marketing surveillance summary statistics.

Lecanemab is dosed by body weight but supplied as fixed-size single-dose vials, which can leave unavoidable leftover drug after preparation. Using published summary statistics from the Japanese lecanemab post-marketing surveillance on body weight, we fitted a body-weight distribution and ran Monte Carlo simulations. Uncertainty was quantified by a parametric bootstrap. With current 200/500-mg vials, mean waste rate was 8.60%. A strategy with 200/250-mg vials reduced waste to 6.30%, and adding a 75-mg vial (≤4 vials/infusion) to 3.67%. At 10,000 person-years, annual waste cost was ∼¥2.36 billion under assumed pricing. Vial-size and dispensing optimization may help reduce avoidable waste.