Healthcare is a highly collaborative environment, where the active sharing of information is central to the care process. Due to the sensitive nature of medical information, care providers are responsible for protecting data, controlling the circumstances in which it is released to others. The publish/subscribe (pub/sub) communication paradigm is useful for data dissemination, as it allows parties to specify their interest in receiving particular information. However, general pub/sub implementation frameworks lack mechanisms to control the flow of data. This paper describes the details of a model to define and enforce fine-grained information sharing policies in an active notification environment. The model, built above a pub/sub middleware, allows policy definitions to control information flow by 1) specifying the conditions for data access, and 2) tailoring information to suit particular circumstances.