Solubility and partition behavior of moxifloxacin: Experimental results and thermodynamics properties

Abstract

The pharmaceutically relevant physico-chemical properties as solubility and lipophilicity of antimicrobial moxifloxacin (MFX) in modelling solvents and biphasic systems were determined using the shake flask method from 293.15 to 313.15 K. The equilibrium MFX solubility (x, mol. frac.) was changed in next order: ethanol (1.08 · 10−2) > 1-octanol (1.18 · 10−3) > buffer pH 2.0 (1.37 · 10−3) > buffer pH 7.4 (6.45 · 10−4) > hexane (1.13 · 10−5). The obtained result good correlated with relative polarity of selected solvents. MFX solubility in buffer solutions is higher in an acid medium, and tends to decrease at increasing pH values, that explained by protolytic properties of compound studied. The experimental solubility values of MFX in selected solvents were mathematically described by two classical models (modified Apelblat and van’t Hoff equations) with good fitting accuracy. A graphical representation of the Hansen solubility parameters for the studied solute/solvent systems is provided in the form of a Bagley diagram. MFX was described as slightly lipophilic drug. Thermodynamic functions of solubility and transfer processes were calculated on base temperature dependencies of solubility and apparent partition coefficients, respectively. The solubility process was characterized as endothermic in the all studied solvents.