The binding of sulphonylureas to serum albumin

The interaction of tolbutamide, glibenclamide, chlorpropamide and tolazamide with serum albumin has been examined. Glibenclamide, the most strongly bound of the four compounds, is bound to only one class of sites. The other three compounds are bound to at least two. The interaction between glibenclamide and albumin was independent of pH and increased markedly with decreasing temperature suggesting that a non-ionic mechanism is involved. In contrast, the overall interaction of tolbutamide with albumin showed little temperature dependence and, in addition, binding of both tolbutamide and chlorpropamide decreased with pH. These findings imply that the predominantly bound species is the anion. Binding parameters corrected for electrostatic effects were found to fit binding data for tolbutamide, chlorpropamide and tolazamide better than uncorrected parameters. Electrostatic correction of binding of glibenclamide is unnecessary.