Isothermal calorimetry is a suitable technique to investigate fluorochemical mediated phase transformations that mimic propellant systems in metered dose inhalers. The early stages of beclomethasone diproprionate (BDP) clathrate formation with using a surrogate propellant (decafluoropentane-HPFP) was measured with isothermal calorimetry. Particles were taken from the isothermal system (TAM) and subject to traditional thermoanalysis to support the clathrate formation hypothesis. Differential scanning calorimetry (DSC) thermograms elicited a decreased onset temperature for crystallisation for each consecutive cycle of perfusion. Thermogravimetric analysis (TGA) analysis demonstrated the embedding of the HPFP moiety within the BDP framework through mass loss proportional to the time spent under elution with HPFP. Fourier Transform Infrared Spectroscopy (FTIR) shows a gradual change in the molecular vibrations as a function of perfusion time with HPFP, yet confirms the bulk of the particles to be characteristic of BDP. This work thus establishes isothermal calorimetry as a useful diagnostic tool in predicting stability in hydrofluoroalkane (HFA) formulations.