Effect of processing conditions and excipients on dehydration kinetics of sodium naproxen hydrate in formulation

The manufacture of oral dosage form may induce changes in the physical form of an active pharmaceutical ingredient. One such example includes formation of hydrate during granulation followed by the reverse transition to the anhydrous form during drying. We used naproxen sodium dihydrate (DH) as the model compound and studied its dehydration at elevated temperature under different processing conditions, (i) in ambient air, (ii) in flow of inert gas (iii) under low pressure environment, and (iv) under 'high' pressure in closed environments. In situ variable temperature X-ray diffraction was used to monitor kinetics of phase transformation under these processing conditions. The DH dehydration was fastest under the flow of inert gas and slowest in closed environment. Polyvinyl pyrrolidone (PVP) and microcrystalline cellulose (MCC), commonly used hygroscopic solids, were used as the model excipients to monitor influence of excipients in modulating DH dehydration behavior under different processing conditions. Both the excipients altered the kinetics as well as the extent of DH dehydration, with PVP delaying and MCC facilitating the transformation under all processing conditions studied. The results indicate that the physical form of API, such as hydrate or anhydrous in the present case, in the formulation may be modulated by rational excipient selection.