Competition between rival brands within the same category gives rise to special competition/substitution effects of great interest to the involved forms. The study of competition in the pharmaceutical market highlights special behavior in the diffusion of knowledge about the products that may differ from other competing arenas. This latent feature naturally affects the evolution of the drugs' performances, in terms of number of packages sold. The aim of this paper is to propose a new model structure within the family of innovation diffusion models that specifically takes the step of knowledge spread into account. We show the application of this model with nonlinear regression methods and a comparison with alternative models to antidiabetic drug sales recorded monthly in the Italian market
