Control strategy for vacuum drying of an API hemihydrate to achieve optimum cycle time and to preserve the water content will be presented. This strategy was established based on understanding of drying kinetics and thermodynamics of hemihydrate derived from experiments in a small Ø 81mm x 50 mm agitated vacuum dryer utilizing online analytical techniques such as diffuse reflectance near infrared (NIR) and headspace mass spectrometry (MS). Comparison of drying results obtained from large scale dryer will also be illustrated.