Asian ginseng, Siberian ginseng, and the Indian Ayurvedic medicine Ashwagandha interfere with serum digoxin measurements obtained with commonly used fluorescent immunoassay tests.

Abbott Laboratories has marketed an alternative digoxin immunoassay, Digoxin III. Researchers at the University of Texas Health Sciences Center at Houston report on the risk of getting inaccurate digoxin levels in patients who take digoxin and one of these herbals at the same time.

First, the details.

• Samples of serum (the fluid part of blood, no cells) that was free of digoxin were spiked with various amounts of Asian ginseng, Siberian ginseng, or Ashwagandha — similar to what might appear in people taking these herbals.
• Then digoxin concentrations were measured.
• Also tested were serum samples taken from patients receiving digoxin, which were then spiked with various amounts of these herbals.

And, the results.

• In serum samples that contained the herbals but not digoxin, the Digoxin III assay reported modest digoxin concentrations.
• When the serum samples of digoxin spiked with the herbals were tested, the presence of the herbals falsely increased the digoxin concentration reported by the new Digoxin III assay.
• Measuring free digoxin (only digoxin not bound to protein) did not eliminate the interference.

The bottom line?
Ginsengs are widely used and have been reported frequently to interfere with the various commercial tests used to measure blood levels of the heart drug, digoxin. A Google search of “ginseng,” “digoxin,” and “assay” returned more than 10,000 results.

Ashwagandha is also a popular Ayurvedic medicine.

In people taking these herbals and digoxin, the caveat to “treat the patient not the lab value” is good advice.

8/4/08 18:15 JR