Complexation of telmisartan with cyclodextrins as a tool of solubility enhancement: A comparative analysis of influence of the cyclodextrin type and method of solid dispersion preparation

Abstract

Cardiovascular telmisartan (TMS) was complexed with modified cyclodextrins (CD) aiming at improvement of its poor solubility which results into low bioavailability. Inclusion complexes with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and sulfobutylether-β-cyclodextrin (SBE-β-CD) in liquid and solid state was evaluated for first time. Phase solubility isotherm diagrams of TMS versus the CD concentration were plotted in a buffer pH 7.4. It was found that TMS/CD complexes are formed in solution in an equimolar stoichiometric ratio of 1:1. The aqueous solubility of TMS with the addition of 0.05 mol·L⁻¹ HP-β-CD increased by 23 times and was 38.9·10⁻⁵ mol·L⁻¹, and the presence of the same amount of SBE-β-CD in solution increased the solubility of the drug by 7 times, reaching a value of 12.6·10⁻⁵ mol·L⁻¹.The binding constants were found to 468 and 114 L·mol⁻¹ for HP-β-CD and SBE-β-CD, respectively. Novel solid forms of TMS with both CDs were prepared using the grinding and evaporation approaches. Successful formation of supramolecular TMS/HP-β-CD and TMS/SBE-β-CD solid complexes was confirmed by FTIR, PXRD, DSC, TGA and SEM. The residual crystallinity of all obtained solid dispersions of TMS/CD did not exceed 10 %. Supersaturation was observed during the dissolution of all the solid complexes. The grinding technique was found to be more advantageous as it ensured the biggest improvement of the drug maximum concentration in the aqueous solution: the TMS solubility in the TMS/HP-β-CD(gr) and TMS/SBE-β-CD(gr) solid complexes increased by 27 and 33 times, respectively. Besides, polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) were tested as crystallization inhibitors. Addition of 1 wt% PVP as a stabilizer is a promising approach for the preparation of TMS pharmaceutical formulations with improved bioavailability.