Propranolol Binding in Plasma during Cardiopulmonary Bypass

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Abstract
The effect of cardiopulmonary bypass on the plasma binding of propranolol was examined in 7 patients. The fraction of propranolol free in plasma doubled, increasing from 6.6-13.5% (P < 0.001) after the administration of heparin, 400 IU/kg. Once cardiopulmonary bypass was concluded and protamine, 8 mg/kg, was given, the free fraction decreased from 13.4 to 8.7% (P < 0.005). There was a further significant decrease to 6.5% over the next 3.1 h (SE .+-. 0.3). Those changes in the free fraction, which would cause more drug being available for binding to receptor sites and for exerting its pharmacologic effect, were due principally to the changes in free fatty acid levels produced by heparin and protamine, and to the hemodilution produced by the pump prime.