Changes in the degree of substitution of HES in vivo and their influence on methods for determining HES concentrations in plasma.

The DS of HES in vivo increases significantly over time. As a result, an HES concentration measured with the enzymatic method in vivo will be significantly lower than the same concentration determined with the o-Toluidine method. In future pharmacokinetic studies, HES concentrations should be measured using a method that takes into account changes in the DS in vivo.