This paper presents a mixed integer linear programing (MILP) model, based on a continuous-time Resource Task Network (RTN) formulation, for the optimal planning/scheduling of biopharmaceutical processes. The model proposes the integration of the production planning with the required downstream maintenance operations, due to performance decay. The model is applied to a literature-based midterm planning problem in the biopharmaceutical industry, addressing the main bioprocesses regulations. Results demonstrate the advantages of a continuous-time formulation to determine the optimal schedule solution and the benefit of incorporating maintenance operation decisions into production planning.