Solubility of silybin in aqueous poly(vinylpyrrolidone) solution

Silybin is a main component in silymarin, which is an antihepatotoxic polyphenolic substance isolated from the milk thistle plant, Silybum marianum. A major problem in the development of an oral solid dosage form of this drug is the extremely poor aqueous solubility. In present work, the solubility of silybin in aqueous poly(vinylpyrrolidone) (PVP k30) solution at the temperature range from 293.15 to 313.15 K was measured by a solid–liquid equilibrium method. Experimental results reveal that the solubility of silybin increases with the increase both in PVPʹs concentration and temperature. With the increase in PVPʹs concentration, the transfer enthalpy for silybin from water to aqueous PVP solution decreases within a negative region, and the transfer entropy increases slightly first in a positive region and then decreases to a negative region. The transfer enthalpy is lower than the entropy term. A modified UNIQUAC model was used to correlate solubility data.