Aqueous solubility of kinase inhibitors: III the effect of acidic counter ion on the dovitinib/γ-cyclodextrin complexation

Cyclodextrins and drug membrane permeation: Thermodynamic considerations

Cyclodextrins are hydrophilic oligosaccharides that can increase aqueous solubility of lipophilic drugs through formation of water-soluble drug/cyclodextrin complexes. Although the complexes are hydrophilic, and as such do not permeate biological membranes, the complexes are known to enhance drug permeation through lipophilic membranes and improve drug bioavailability after, for example, oral administration. However, it is not clear how cyclodextrins enhance the permeation. An artificial biomembrane (PermeaPad®) was used to study the effect of donor medium composition on drug permeation. It was observed that in aqueous solutions the hydrophilic cyclodextrins behave not like disperse systems but rather like organic cosolvents such as ethanol, increasing the solubility without having significant effect on the molecular mobility and ability of lipophilic drug molecules to partition into the lipophilic membrane. Also, that partition of dissolved drug molecules from the aqueous exterior into the membrane is at its maximum when their thermodynamic activity is at its maximum. In other words, that drug flux from aqueous cyclodextrin solutions through lipophilic membranes depends on both the concentration and the thermodynamic activity of dissolved drug. Maximum flux is obtained when both the drug concentration and thermodynamic activity of the dissolved drug molecules are at their maximum value.

Preformulation studies of dovitinib free base: Solubility, lipophilicity and stability

Dovitinib has been investigated as an anti-tumor drug due to its ability to inhibit multiple receptor tyrosine kinases. Dovitinib free base has a poor water solubility leading to poor absorption. Salts and lipid-based formulations have been used to improve drug availability. Here, we investigated the physiochemical properties of the dovitinib free base in the presence of some pharmaceutical excipients. We sought to study the effect of acidic counterions on the aqueous solubility and lipophilicity of dovitinib and how pH, buffer species, and cyclodextrin (CD) influenced dovitinib stability. pH-solubility studies were performed by titration against five different acids. Aqueous solubility of dovitinib salt depended on the counterion. Lactic acid greatly increased the aqueous solubility of dovitinib. The counterion effect on the solubility was also investigated in the aqueous complexing media. Unexpected synergistic solubilization was found with γ-CD/phosphoric acid and γ-CD/maleic acid. The counterion did not affect the lipophilicity of dovitinib at physiological pH. Accelerated degradation of dovitinib was carried out at high temperature. Stability was studied across a range of pH values, buffer species and in the presence of two CDs. Dovitinib was most stable at pH 4 in the phosphate buffer species. γ-CD stabilized the drug at relatively low pH.