Über den Einfluß verschiedener Pharmaka auf die Eiweißbindung von Phenolrot und Digitoxin

Summary

The binding of phenol red and digitoxin to bovine albumin has been measured by means of equilibration dialysis and characterized by the following parameters: binding constant K ₁, number of binding sites per albumin molecule n, and free binding energy DF ^o.

Protein binding of phenol red yields a saturation type curve with saturation at about 11.3 mmole/l.

Phenylbutazon and probenecid were able to displace phenol red from albumin binding sites in concentrations which are regularly reached after therapeutic doses.

With digitoxin because of its hydrophobic character plasma binding could not be measured beyond concentrations of 0.82 mmole/l. Though in principle there is no difference between phenol red and digitoxin binding (a digitoxin binding curve could be calculated also for high concentrations) no displacement effect was seen with probenecid, phenylbutazon, salicylic acid and benzbromaron up to tenfold therapeutic plasma levels.

These drugs were effective, however, in the displacement of digitoxin in diluted plasma albumin solutions. This indicates that for an effective displacement multiple molar concentrations of bound and displacing drug with respect to the binding protein are necessary. Displacement from plasma protein therefore plays no role in the possible interference of drugs if one of them is applied in doses far below the molar concentration of the binding proteins.