[Simplified rapid determination of plasma digoxin. Methods and clinical evaluation].

The introduction of the Gamma Coat 125I-Digoxin Radioimmunoassay has simplified the digoxin determination to an extent that it may be used even in general hospitals with an intensive care unit. The total time for a stat determination has been reduced to 70 min. The coefficient of variation of the digoxin determination at low levels (less than 0.8 ng/ml) was less than 15% for simultaneous and repeated measurements even when using one of the inexpensive nuclear counting systems. At high levels (greater than 2.5 ng/ml) the coefficient of variation showed to be less than 6%. Hemolysis, low albumine concentration and other than digoxin-bound isotopes in the blood samples did not cause methologic problems. Provided that resorption and elimination kinetics of the different digoxin preparations were taken into account, digoxin levels of more than 2 ng/ml as measured by the Gamma Coat method in patients with normal renal function plasma were usually associated with clinical signs of overdosage; therapeutic concentrations were mostly higher than 1.2 ng/ml. The incidence of digitalis toxicity with high digoxin levels was lower in uremic than in normal patients. According to preliminary observations in dialysis patients this increase in tolerance to digitalis, may be a consequence of hyperkalemia and renal acidosis. Erroneously high digoxin concentrations were found in patients up to 2 hrs after injection of high doses of spironolactone (400-1000 mg) due to cross reaction. Therapeutic concentrations of digitoxin (10-25 ng/ml) caused only subtherapeutic digoxin concentrations of 0.4-0.9 ng/ml.