[Radionuclide methods of determining digoxin levels]

The digoxin level in the blood was determined in 92 patients with blood circulatory insufficiency using radioimmunoassays (Sea Ire-Sorin kits) and radionuclide (86 Rb) methods. Pharmacokinetics of digoxin was evaluated on the basis of a two-compartmental mathematical model (by J. Y. Wagner). Direct correlation between the value of a maintenance dose and digoxin concentration in the blood was established. Digoxin values in the blood determined by the radionuclide method, were somewhat higher than the indices of the radioimmunological method. According to this method digoxin therapeutic concentrations in the blood were: 0.4-2.8 ng/ml; according to the radionuclide method 0.6-4.8 ng/ml. Symptoms of digoxin intoxication (overdosage) in rising its concentration in the blood up to 1.1-3.3 ng/ml by the radioimmunoassay and up to 2.2-6.1 ng/ml by the radionuclide method were recorded. It can be accounted for by the fact that bigger values of digoxin active metabolites are determined by the radionuclide method, whereas the radioimmunoassay is more specific to digoxin. Pharmacokinetic parameters (distribution volume, digoxin clearance, the period of semi-elimination) calculated by two methods, brought about the same results. Regularities of the changes of digoxin pharmacokinetics in patients with disturbed renal function are analysed.