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November 17, 1978

Digoxin Serum Levels

Author Affiliations

University of Iowa College of Pharmacy Iowa City

JAMA. 1978;240(21):2248-2249. doi:10.1001/jama.1978.03290210030014

To the Editor.—  The article by James E. Doherty, MD, "How and When To Use the Digitalis Serum Levels" (239:2594, 1978), presents brief but concise guidelines in the interpretation of serum digitalis measurements. Dr Doherty's discussion of the pitfalls of interpretation includes medications known to interfere with digoxin absorption, but fails to include other commonly used medications reported to give falsely elevated serum digoxin assay results.The radioimmunoassay of digoxin can be performed using tritiated digoxin (3H) or a radioiodinated tracer (125I monoiodinated 3-succinyl digoxigenin-1-tyrosine).1 A number of investigators2-4 have reported various factors affecting the results for radioimmunoassay of digoxin using the tritiated tracer. Human steroids and drugs with a steroid structure similar to that of digoxin can interfere because of cross-reaction.2 Drugs reported to cross-react with the radioimmunoassay using the tritiated tracer include spironolactone,2-4 prednisone,2,3 prednisolone,2,3 and the cardiac glycosides.1,3,4