Effect of albumin on serum digoxin radioimmunoassays.

Clinical Chemistry (Impact Factor: 7.15). 04/1975; 21(3):402-6.
Source: PubMed

ABSTRACT The use of certain commerically available radioimmunoassay kits for measurement of digoxin results in errors in the determined digoxin concentration of patients when these kits are used according to manufacturers' directions. One factor that is, in part, responsible for these errors is a difference between standards and samples with respect to albumin concentration. Three of the four kits investigated showed a significant inverse relationship between the albumin concentration in the sample and the binding of radiolabeled digoxin by its antibody when the albumin concentration was varied over an extended range. It is apparent, however, that differences in albumin concentration do not completely explain the observed variations in the assay values.

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    ABSTRACT: Between-sample variation in tracer binding in the 125I-labeled digoxin radioimmunoassay was investigated with two tracers, 3-O-succinyl-digoxigenin-[125I]-labeled tyrosine and [125I]-labeled tyrosine-methyl-ester-digoxin. Digoxin-free serum samples having various concentrations of thyroxine were assayed with both tracers. The percentage of tracer bound when the samples were assayed with the first-mentioned tracer was increased significantly for the low thyroxine groups when compared to the normal (P less than 0.001) or the high thyroxine groups (P less than 0.05). Little difference existed when the latter tracer was used. There was variation in tracer binding when serum from dogs dosed with thyrotropin was assayed with the first tracer, but there was little variation with the second. Tracer binding may be influenced by thyroxine-binding proteins. Variation in tracer binding appears to be reduced when [125I]-labeled tyrosine-methyl-ester-digoxin is used.
    Clinical Chemistry 11/1976; 22(10):1732-4. · 7.15 Impact Factor
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    ABSTRACT: A study designed to investigate the relationship between the pharmacokinetics of digoxin and a measure of its pharmacological effect has been conducted. Serum digoxin concentrations and systolic time intervals were measured concurrently in 12 normal male volunteers following a 1.0 mg i.v. bolus injection. The averaged serum digoxin concentration--time and response--time data were analyzed pharmacokinetically using a three-compartment open model and nonlinear least-squares fitting. When only the serum level--time data were analyzed, a close relationship was found between calculated digoxin levels in the slowly distributing (deep) peripheral compartment and response of the heart to digoxin, as measured by changes in the QS2 index (delta QS2I). Although it was not possible to distinguish clearly a linear from a nonlinear relationship between digoxin levels in the deep compartment and delta QS2I, the nonlinear relationship gave the best overall fit when both serum digoxin and delta QS2I data were fitted simultaneously. The simultaneous fit yielded a total body clearance of digoxin of 3.6 ml/min/kg and a terminal t1/2 of 42 hr.
    Journal of Pharmacokinetics and Biopharmaceutics 03/1979; 7(1):47-61.


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