Determination of cardiac and plasma drug levels during long-term amiodarone therapy.

A study of plasma and cardiac concentrations of amiodarone during the course of long-term oral therapy was made possible by the improvement of analytical high performance liquid chromatography of plasma and tissue extracts. The plasma level was found to increase linearly with the daily dose of the drug, above a threshold value of c. 1 . 9 mg kg-1 day-1. Similarly, the cardiac content increased linearly with the daily dose, with no threshold, showing that the drug is taken up and accumulated in the cardiac tissue, with no obvious difference between atrial and ventricular samples (P greater than 0 . 05). Both plasma and heart showed no saturation at high drug intake, a justification for increasing the oral intake in severe cases. The linear relationship between tissue and blood concentrations allows a prediction of the cardiac level from a simple and routine blood analysis.