Demand Uncertainty, Perishability and Disruption: A Systematic Literature Review of Inventory Decision Factors in Pharmaceutical Multi-Echelon Supply Chains

Pharmaceutical multi-echelon supply chains face considerable inventory-management challenges arising from demand uncertainty, product perishability, production-capacity limitations, and supply-chain disruptions. This study conducts a systematic literature review (SLR) to examine inventory-management techniques and to identify the critical factors influencing inventory optimization in pharmaceutical multi-echelon supply chains. Following the PRISMA protocol, eighteen peer-reviewed studies published between 2021 and 2026 and indexed in Scopus and ScienceDirect were selected. The review shows that demand stochasticity, forecast uncertainty, service-level requirements, and multi-echelon synchronization are the most frequently examined factors affecting inventory performance. Stochastic inventory optimization, multi-echelon inventory optimization, multi-objective optimization, and AI/DRL-based inventory optimization are the most widely used methods for improving inventory effectiveness, contributing to cost minimization, stockout reduction, and higher service levels. Nevertheless, research gaps remain in integrating shelf-life and expiration-risk considerations, production planning, sustainability, and disruption management within unified inventory-optimization frameworks.