Solid-liquid equilibrium and distribution in pharmaceutically relevant media of cardiovascular sotalol hydrochloride

The shake-flask method was used to determine the solubility of sotalol hydrochloride (STL), a cardiovascular drug, in solvents modeling a variety of body media within the temperature range (293.15–313.15) K. In the descending order of the drug solubility the solvents can be arranged as follows: buffer pH 2.0, buffer pH 7.4, 1-octanol, n-hexane. The experimental values of solubility of the drug in aqueous solvents agree well with the calculated values of the pH-solubility profile. The study shows that the maximum solubility of the salt is observed within the pH range from 2.9 to pH_max equal to 6.1. Temperature dependencies of the STL distribution coefficients were obtained in 1-octanol/buffer pH 7.4 and n-hexane/buffer pH 7.4 systems. Since the values of the partition coefficients of hydrophilic STL are low, it was concluded that the diffusion through the lipid biolayer of cell membranes was unfavorable and that the paracellular transport of the drug molecules might prevail. The thermodynamic functions of dissolution and transfer were calculated and discussed taking into account the physicochemical properties of STL and the solvents used.