This paper focuses on efficient e-procurement mechanisms that enable hospitals and pharmaceutical suppliers to electronically exchange contractual information, aided by the technologies of optimisation and business rules. E-procurement offers hospitals and ambulatory facilities several notable advantages: convenience, efficiency, broad selection, favourable pricing, information on new products and even more. Optimisation and business rules technologies can help meet buyers' needs and bring a higher level of efficiency to key tasks such as formatting multi-supplier catalogues, costing out indirect procurement alternatives, optimising the sourcing of indirect goods and services, mapping approval processes and following the progress of specific purchase orders. This article presents EPOS which is triggered by the consumer's request, offers the participants the ability to dynamically constellate with other medical suppliers, and promotes collective competition among the constellations.