[Significance of serum digoxin concentration and its influencing factors]

In recent years it has become possible by means of a radioimmunoassay to measure Digoxin concentration in the serum of digitalized patients. With this method it could be shown that the resorption of Digoxin is decreased by partial resection of the samll intestines, by malabsorption syndromes, after ingestion of Neomycin, Colestyramine and antacids. In renal insufficiency, however, the elimination half-life period of Digoxin is increased conspiciously (from about 35 hours up to about 120 hours). This results in a raised serum concentration of cardiac glycosides unless the dosage is decreased considerably. The incidence of Digitalis intoxication in Digitalis treated patients has been reported to rank as high as 20%. There is, however, no strict correlation between the serum glycoside level and the clinical symptoms, because the glykoside concentration in the serum does not represent the pharmacologically active concentration at the receptor. Experimental investigations of cardiac glycoside binding to the receptor for cardiac glycosides in human heart cell membranes revealed, that receptor bound Digoxin for instance is diminished in serious renal insufficiency and it depends on the serum concentration of potassium, calcium and magnesium. In hypoxia, after myocardial infarction and in myxedema the sensitivity for cardiac glycosides is increased. The opposite is true in hyperthyreoidism, fever and in children. All of these factors have to be kept in mind and paid attention to in the clinical evaluation of the measured Digoxin concentration in the serum.