The influence of blood collection technique on serum and plasma protein binding of disopyramide

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Abstract
Serum and plasma disopyramide (D) protein binding was compared after blood was collected from four normal subjects in various Vacutainer® tubes. The fraction of disopyramide bound to proteins in control serum and plasma was drug concentration dependent and correlated well with the capacity factor (N) associated with a high affinity protein binding site. D free fraction increased 60% at a post-equilibrium concentration of 2 µg/ml in plasma following exposure of blood to green-top Vacutainer® stoppers due to a 60% reduction in the affinity constant associated with the high affinity protein binding site. Heparin and EDTA had no effect on the plasma protein binding of D. These results suggest a competitive inhibition of disopyramide binding to α1-acid-glycoprotein following contact of blood with rubber Vacutainer® stoppers.