Densities of solutions of the chiral (in the racemic form) trans-dimethyldiethylglycoluril (1,4-diethyl-3,6-dimethyltetrahydroimidazo[4,5-d]imidazole-2,5(1H, 3H)-dione), being a promising tranquilizer Albicar, in ordinary (H2O) and heavy (D2O) water were measured using the Anton Paar DMA 5000 M high-precision vibrating tube densimeter. All experiments were performed within the temperature range between 278.15 K and 318.15 K (with a step of 10 K) at the pressure to be ca. 99.6 kPa. The solution aquamolality was ranged from ca. 0.02 to ca. 0.2 mol (55.51 mol of solvent)(-1) for each of H/D isotopically distinguishable systems compared. The standard (partial at infinite dilution) molar volumes as well as expansibilities of the solute were derived from the solution density data. The behavior of solvent isotope effects (IEs) on the considered quantities were described taking account of structure-and interaction-related features of H2O and D2O media. It was confirmed that the Albicar hydration is enhanced overall in the D2O medium. The volumetric characteristics for the heterocyclic solute being studied were discussed in comparison with those for Mebicar (1,3,4,6-tetramethyl-derivative) and Bicaret (1,3,4,6-tetrae thyl-derivative), using the previous our results. (C) 2017 Elsevier Ltd.