Urea inclusion compounds of enalapril maleate for the improvement of pharmaceutical characteristics

Urea is a well known adductor for linear organic compounds. In the present study, enalapril maleate, a substituted cyclic organic compound, was successfully included in urea together with a suitable rapidly adductible endocyte (RAE). Formation of the urea inclusion compound was confirmed by Fourier transform infrared spectroscopy, differential scanning calorimetry and X-ray diffraction. The modified Zimmerschied calorimetric method was used to estimate the minimum amount of RAE required for adduction of enalapril maleate in urea. Urea-enalapril maleate-RAE inclusion compounds containing varying proportions of guests were prepared and their thermal behaviour studied by differential scanning calorimetry. Regression analysis revealed an excellent r² value with regard to the influence of the relative proportion of RAE on the heat of decomposition. The inclusion compounds were found to exhibit good content uniformity and improved dissolution profile as demonstrated by increased dissolution efficiency. Studies revealed that urea inclusion may be a promising alternative for the formulation of potent poorly soluble drugs into immediate release products.