Thecocrystals and salts of an antiallergic drug, tranilast, were synthesizedto improve its solubility and photostability. Two tranilast cocrystalswith urea (1) and nicotinamide (2), as wellas two salts with cytosine (3) and sodium ion (4), were obtained and characterized by infrared spectra, thermogravimetricanalyses, differential scanning calorimetry, and powder and singlecrystal X-ray diffractions. The results of single crystal structureanalyses of 1–3indicate that tranilastcombines amide groups in coformers via R22(8) synthon, resulting in a 1:1 stoichiometry.The complexes showed advantages in terms of solubility and photostabilityin comparison to pure tranilast. The maximum solubility values of 1–3in phosphate buffer of pH 6.8 areapproximately 1.6, 1.9, and 2.0 times as large as that of tranilast,and the residual of tranilast is 79.5, 92.9, 88.5, 86.2, and 87.4%for tranilast and 1–4, respectively,under the fluorescent lamp irradiation for 96 h. [ABSTRACT FROM AUTHOR]