Abstract
We present an Agent-Based Model (hereafter ABM) for a pharmaceutical supply chain operating under conditions of weak regulation and imperfect information, exploring the possibility of poor quality medicines and their detection. Our interest is to demonstrate how buyers can learn about the quality of sellers (and their medicines) based on previous successful and unsuccessful transactions, thereby establishing trust over time. Furthermore, this network of trust allows the system itself to evolve to positive outcomes (under some but not all circumstances) by eliminating sellers with low quality products. The ABM we develop assumes that rational and non-corrupt agents (wholesalers, retailers and consumers) learn from experience and adjust their behaviour accordingly. The system itself evolves over time: under some - but not all - circumstances, sellers with low-quality products are progressively eliminated. Three distinct states of the supply chain are observed depending on the importance of trust built up from past experience. The 'dynamic' state is characterised by a low level of trust leading to a continually changing system with new drugs introduced and rejected with little regard to quality. The 'frozen' state arises from high levels of reliance on past experience and locks the supply chain into a suboptimal state. The 'optimising' state has moderate reliance on past experience and leads to the persistence of suppliers with good quality; however, the system is still 'invadable' by better quality drugs. Simulation results show that the state reached by the system depends strongly on the precise way that trust is established: Excessive levels of trust make it impossible for new, improved treatments to be adopted. This highlights the critical need to understand better how personal experience influences consumer behaviour, especially where regulation is weak and for products like medicines whose quality is not readily observable.
Highlights
Introduction. Insecurity and permeability of pharmaceutical supply chains constitute a major global public health threat
We designed a simple model for a self-organising supply chain for pharmaceutical drugs which attempted to balance simplicity, existing modelling ideas and compatibility with ethnographic fieldwork in Ghana and Tanhttp://jasss.soc.surrey.ac.uk/ / / .html zania
It o ers the possibility for buyers to discover the quality of the drugs supplied by sellers based on inspections or medical outcomes, both of which are subject to stochastic error
Summary
. Insecurity and permeability of pharmaceutical supply chains constitute a major global public health threat. Over % of pharmaceutical medicines consumed in low/middle-income countries (LMIC) are thought to be sub-standard or falsified (SF)(WHO b; Almuzaini et al ; Kaur & Singh ; Newton et al ; Nayyar et al ), containing little or no active ingredient (WHO, a; b), with rates of over % reported in parts of Sub-Saharan Africa. . E orts to tackle the SF medicine threat have addressed both the supply side (tightening regulation, improving detection rates and prosecuting o enders) and the demand side, though education programmes aimed at health professionals and the general public (Cinnamond & Woods ; Hamilton et al ; WHO b). A combination of limited regulatory resources (financial/human), endemic malpractice/corruption, and the promise of potentially huge profits, confound efforts to prevent poor-quality medicines entering supply chains Nayyar et al ( ); Newton et al ( ).
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