Two Polymorphic Cocrystals of Theophylline with Ferulic Acid

Abstract

In this study, the crystal structures of 1:1 theophylline–ferulic acid cocrystal polymorphs are reported for the first time. Interestingly, both forms crystallize in the same space group but with a different number of molecules in the asymmetric unit (form I = 2; form II = 4). The two polymorphs show distinct crystal morphology, demonstrating prism and rod single crystals, respectively. Theoretical calculations are performed to predict their morphology and thermodynamic stability (form I > form II). The prediction result agrees well with the measured pharmaceutical properties. Form I presents better hygroscopic stability (RH < 95%), slower dissolution, and lower solubility (1.06 ± 0.03, 1.63 ± 0.01, 1.30 ± 0.08 and 4.09 ± 0.05 mg/mL in water, pH = 1.2, pH = 4.5 and pH = 6.8 buffered solutions) over form II (8.45 ± 0.33, 2.41 ± 0.17, 3.46 ± 0.26 and 28.71 ± 0.87 mg/mL in water, pH = 1.2, pH = 4.5 and pH = 6.8 buffered solutions). In summary, this work elucidates the experimental findings with relevant predictions systematically and enriches our understanding of the structure–property relationship of the theophylline cocrystal system.