Altered drug binding due to the use of indwelling heparinized cannulas (heparin lock) for sampling

Abstract

The effect of the use of the so‐called heparin lock for blood sampling on the binding of propranolol has been studied and a cumulative dose‐response curve to heparin constructed. The use of this method of blood sampling introduced considerable artifactual changes into the measurement of propranolol's plasma binding. The free fraction rose from 9.9% to 13.4% after only 50 U of heparin was used to flush the cannula. The increase in the free fraction of propranolol showed excellent correlation with the increase in free fatty acid levels (p < 0.001, r = 0.996). The importance of ensuring that sampling techniques do not introduce artifactual changes in pharmacokinetic studies is emphasized.