Abstract
Asian ginseng, Siberian ginseng, and Indian Ayurvedic medicine Ashwagandha demonstrated modest interference with serum digoxin measurements by the fluorescent polarization immunoassay (FPIA). Recently, Abbott Laboratories marketed a new digoxin immunoassay, Digoxin III for application on the AxSYM analyzer. We studied potential interference of these herbal supplements on serum digoxin measurement by Digoxin III assay in vitro and compared our results with the values obtained by Tina‐quant assay. Aliquots of drug‐free serum pool were supplemented with various amounts of Asian ginseng, Siberian ginseng, or Ashwagandha approximating expected concentrations after recommended doses and overdoses of these herbal supplements in serum. Then digoxin concentrations were measured by the Digoxin III and Tina‐quant (Roche Diagnostics) assay. We also supplemented aliquots of a digoxin pool prepared from patients receiving digoxin with various amounts of these herbal supplements and then measured digoxin concentrations again using both digoxin immunoassays. We observed modest apparent digoxin concentrations when aliquots of drug‐free serum pool were supplemented with all three herbal supplements using Digoxin III assay (apparent digoxin in the range of 0.31–0.57 ng/ml), but no apparent digoxin concentration (except with the highest concentration of Ashwagandha supplement for both brands) was observed using the Tina‐quant assay. When aliquots of digoxin pool were further supplemented with these herbal supplements, digoxin concentrations were falsely elevated when measured by the new Digoxin III assay. For example, we observed 48.2% (1.63 ng/ml digoxin) increase in digoxin concentration when an aliquot of Digoxin pool 1 (1.10 ng/ml digoxin) was supplemented with 50 μl of Asian ginseng extract (Brand 2). Measuring free digoxin does not eliminate the modest interferences of these herbal supplements in serum digoxin measurement by the Digoxin III assay. J. Clin. Lab. Anal. 22:295–301, 2008. © 2008 Wiley‐Liss, Inc.