We present a planning method for reducing product losses while manufacturing sterile drug products. The method consists of five steps that guide the process improvement effort and serve as a foundation for the Plan phase of the Plan-Do-Check-Act cycle. The method can cover all product components of the process in the analysis (e.g., active pharmaceutical ingredients, excipients, and primary packaging materials). In addition, newly developed mechanisms help generate effective improvement scenarios and allow for comparing the effect and difficulty of different scenarios in a multiobjective manner. In a case study, the method was executed step-by-step using industrial data, and its effectiveness was demonstrated.