Effect of Spironolactone, Potassium Canrenoate and Their Common Metabolite Canrenone on Serum Digoxin Measurement by Digoxin III, a New Digoxin ImmunoassayDasgupta, Amitava PhD*; Tso, Gertie MT(ASCP)†; Wells, Alice MT(ASCP)*Therapeutic Drug Monitoring: December 2008 - Volume 30 - Issue 6 - p 744-747 doi: 10.1097/FTD.0b013e31818b0e6a Short Communication Buy Abstract Author InformationAuthors Article MetricsMetrics Spironolactone and potassium canrenoate (aldosterone antagonist diuretics) are often used with digoxin in clinical practice. It has been well documented in the literature that spironolactone, potassium canrenoate, and their common metabolite canrenone cross-react with several digoxin immunoassays at concentrations expected after therapeutic usage of these drugs and falsely elevate or lower serum digoxin concentrations. Recently, Abbott Laboratories marketed a new Digoxin III immunoassay for application on the AxSYM analyzer. We studied the potential interference of these compounds with this new digoxin assay. The Tina-quant assay was used as the reference method because spironolactone, potassium canrenoate, and canrenone do not interfere with serum digoxin measurement using this assay. Aliquots of drug-free serum were supplemented with therapeutic and above therapeutic concentrations of spironolactone, canrenone, and potassium canrenoate, and apparent digoxin concentrations were measured using the Digoxin III assay and Tina-quant assay. Significant apparent digoxin concentrations were observed when the Digoxin III digoxin assay was used, but no apparent digoxin levels was observed using the Tina-quant assay. When serum pools prepared from patients receiving digoxin were further supplemented with these compounds in concentrations expected in sera of patients receiving these medications, falsely elevated digoxin levels were observed using Digoxin III assay, but no statistically significant change was observed using the Tina-quant assay. We conclude that spironolactone, potassium canrenoate, and their common metabolite canrenone interfere with the serum digoxin measurements using the new Digoxin III assay. From the *Department of Pathology and Laboratory Medicine, University of Texas Health Sciences Center at Houston, Houston, and †Memorial-Hermann Hospital Laboratory Services, Houston, Texas. Received for publication May 4, 2008; accepted July 17, 2008. Correspondence: Dr. Amitava Dasgupta, Department of Pathology and Laboratory Medicine, University of Texas Medical School at Houston, 6431 Fannin, MSB 2.292, Houston, TX 77030 (e-mail: firstname.lastname@example.org). © 2008 Lippincott Williams & Wilkins, Inc.