Homogeneous Immunoassays—Therapeutic Drug Monitoring
Innofluor®—Fluorescence Polarization Immunoassays To view and print the files below you will need Adobe Acrobat Reader®,
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INNOFLUOR® Digitoxin Assay System
The INNOFLUOR® DIGITOXIN Assay System is intended for the quantitative determination of total digitoxin in serum for therapeutic drug monitoring by fluorescence polarization immunoassay (FPIA). The assay system is for use on the TDx® or the TDxFlxTM (TDx®/TDxFLx®) analyzer.
Digitoxin is a cardiac glycoside prescribed for the treatment of congestive heart failure and cardiac arrhythmias.1,2 Cardiac glycosides appear to inhibit membrane-bound Na,K-ATPase which leads to increased calcium availability and results in improved cardiac muscle contractions.2,3
Digitoxin is routinely administered orally. At steady state, digitoxin is distributed in most body tissues and is over 90% protein bound in plasma.1,2 Digitoxin is metabolized in the liver, excreted with the bile into the intestine and recirculated through the liver until completely metabolized.1 Metabolism is complex and results in the formation of many metabolites, which are primarily inactive and are probably excreted in the urine.4,5 Digoxin is also a metabolite but comprises only a small fraction of the total metabolites during chronic therapy.1,4 The long elimination half-life of 6-8 days is most likely due to the firm binding of digitoxin to protein and is not significantly affected by liver disease.1,2,6
Cardiac glycosides have a narrow therapeutic range and are frequently toxic, with many of the toxicity symptoms similar to symptoms of the underlying disease.1-3,7 It is important to monitor serum levels in combination with information provided by clinical data to avoid toxicity while maintaining adequate dosin.4,5
Barnhart ER. Pub. Physician’s Desk Reference. Oradell, NJ: Medical Economics Co., Inc., 1991: 1222-1223.
Hoffman BF, Bigger JT Jr. Digitalis and allied cardiac glycosides. In: The pharmacological basis of therapeutics, Goodman Gilman A, et. al., eds. Pergamon Tress Inc., New York 10523 1990; 814-839.
Meyers FH. Jawetz E, Goldfin A. Digitalis. In: Review of medical pharmacology, 7th ed. Los Altos CA: Lange Medical Publications, 1980: 135-146.
Baselt RC. Digitoxin. In: Disposition of toxic drugs and chemicals in man, 2nd ed. Davis, CA: Biomedical Publications, 1982: 251-253.
Castle MC, Zavecz JH. Comparison of digitoxin and its major glucuronidated metabolite: inhibition of Na-K-ATPase and reactivity with the radioimmunoassay. Res Comm Clin Path Pharm 1987; 56(1): 33-48.
Bussey HI, Hawkins, DW, et al. A comparative trial of digoxin and digitoxin in the treatment of congestive heart failure. Pharmacoltherapy 188; 8(4): 235-240.
Kelly RA, Smith TW. Recognition and management of digitalis toxicity. Am J Cardiol 1992; 69: G108-109.
