title: Theophylline-nicotinamide cocrystal formation in physical mixture during storage.
abstract: Pharmaceutically relevant properties, such as solubility and dissolution rate, of active pharmaceutical ingredients can be enhanced by cocrystal formation. Theophylline and nicotinamide are known to form cocrystals, for example if subjected to solid-state grinding. However, under appropriate conditions, cocrystals can also form in physical mixtures without any mechanical activation. The purpose of this work was to study whether theophylline and nicotinamide could form cocrystals spontaneously, without mechanical activation. Crystalline theophylline and nicotinamide powders were gently mixed manually in a 1:1 molar ratio and stored at different relative humidity and temperature conditions. The solid state of the samples was analyzed by differential scanning calorimetry, Raman spectroscopy and X-ray powder diffractometry. Three different variations of theophylline were used as starting materials, e.g., two size fractions of theophylline anhydrate (large 710 μm-1 mm and small 180-355 μm), and monohydrate (recrystallized from water). As a reference, anhydrous theophylline-nicotinamide cocrystals were prepared by solid-state grinding. The results of this study indicate that theophylline-nicotinamide cocrystals can form without any mechanical activation from physical mixtures of theophylline and nicotinamide during storage. For anhydrous samples, storage humidity was found to be a critical parameter for cocrystal formation. Increasing temperature was also found to have an accelerating effect on the transformation. The effect of particle size of anhydrous theophylline on the transformation rate could not be completely resolved; DSC and Raman indicated slightly faster transformation with a physical mixture prepared from large size fraction of anhydrous theophylline, but the differences were only minor. Cocrystal formation was also observed in the physical mixture prepared from theophylline monohydrate, but the rate was not as high as with samples prepared from anhydrous material.
authors: School of Pharmacy, Pharmaceutical Technology, Faculty of Health Sciences, University of Eastern Finland, Kuopio Campus, Finland. Electronic address: Tuomas.Ervasti@uef.fi.
authors: Tuomas
authors: T
authors: Ervasti
authors: School of Pharmacy, Pharmaceutical Technology, Faculty of Health Sciences, University of Eastern Finland, Kuopio Campus, Finland.
authors: Jaakko
authors: J
authors: Aaltonen
authors: School of Pharmacy, Pharmaceutical Technology, Faculty of Health Sciences, University of Eastern Finland, Kuopio Campus, Finland.
authors: Jarkko
authors: J
authors: Ketolainen
mesh_terms: D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D004356:Drug Storage; D006813:Humidity; D009536:Niacinamide / Q000737:chemistry*; D033362:Powder Diffraction; D013059:Spectrum Analysis, Raman; D013696:Temperature; D013806:Theophylline / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D009536:Niacinamide; D013806:Theophylline
keywords: Cocrystal; DSC; Nicotinamide; Raman-spectroscopy; Theophylline; XRPD