1298 Arch Pathol Lab Med—Vol 131, August 2007 Ashwagandha and Digoxin Assay—Dasgupta et al Effect of Indian Ayurvedic Medicine Ashwagandha on Measurement of Serum Digoxin and 11 Commonly Monitored Drugs Using Immunoassays Study of Protein Binding and Interaction With Digibind Amitava Dasgupta, PhD; Amanda Peterson, MD; Alice Wells, MT(ASCP); Jeffrey K. Actor, PhD ● Context.—Ashwagandha, a popular Ayurvedic medicine, is now available in the United States. Alkaloids found in this herb have structural similarity with digoxin. Objective.—To study potential interference of Ashwa- gandha with serum digoxin measurement by immunoas- says. Potential interference was also investigated with im- munoassays for 11 other commonly monitored drugs. In addition, interaction of components of Ashwagandha with the Fab fragment of antidigoxin antibody (Digibind) was investigated. Design.—Two different brands of liquid extract and 1 dry powdered form of Ashwagandha were used for this inves- tigation. Aliquots of drug-free serum were supplemented with various concentrations of Ashwagandha and apparent digoxin concentrations were measured by 3 digoxin im- munoassays. Mice were fed with Ashwagandha and appar- ent digoxin concentrations were measured 1 and 3 hours after feeding. Potential interference of Ashwagandha with immunoassays of 11 other drugs was also investigated. In- teraction of components of Ashwagandha with Digibind was studied in vitro. Results.—Significant apparent digoxin concentrations were observed both in vitro and in vivo using the fluores- cence polarization immunoassay of digoxin, whereas the Beckman and the microparticle enzyme immunoassay di- goxin assay demonstrated minimal interference. Immuno- assays of 11 other drugs tested were unaffected. When Ash- wagandha extract was added to a serum pool containing digoxin, falsely elevated digoxin value was observed with fluorescence polarization immunoassay, but values were falsely lowered when measured by the microparticle en- zyme immunoassay. Digibind neutralized digoxin-like im- munoreactive components of Ashwagandha in vitro. Conclusions.—Components of Ashwagandha interfered with serum digoxin measurements using immunoassays. Digibind neutralized free digoxin-like immunoreactive components of Ashwagandha. (Arch Pathol Lab Med. 2007;131:1298–1303) A shwagandha (Withania somnifera), also known as win- ter cherry, belongs to the pepper family and is found in India and Africa, as well as in North America. Ash- wagandha roots have been used in Indian Ayurvedic medicine for more than 3000 years as an aphrodisiac, liver tonic, anti-inflammatory agent, and astringent. Traditional use of Ashwagandha among tribal peoples in Africa in- cludes treating fever and inflammatory conditions. Prelim- inary research indicates that Ashwagandha may be effec- tive for treating anxiety, cognitive and neurologic disor- ders, inflammation, and Parkinson disease. 1 Recently, sev- eral preparations of St John’s wort were found to contain extract of Ashwagandha, as revealed by surveying prod- uct from several herbal stores in the Houston area. Ash- wagandha extract is also used traditionally in Ayurvedic Accepted for publication February 2, 2007. From the Department of Pathology and Laboratory Medicine, Uni- versity of Texas, Houston. The authors have no relevant financial interest in the products or companies described in this article. Reprints: Amitava Dasgupta, PhD, Department of Pathology and Lab- oratory Medicine, University of Texas, 6431 Fannin, MSB 2.292, Hous- ton, TX 77030 (e-mail: Amitava.Dasgupta@uth.tmc.edu). medicine for stimulation of the heart. However, pharma- cologic and toxicologic effects of Ashwagandha on hu- mans have not been established by rigorous scientific re- search. The major biochemical constituents of Ashwagandha are steroidal alkaloids and steroidal lactones in a class of compounds termed withanolides. Withaferin A (also a with- anolide), a major constituent of Ashwagandha, has struc- tural similarity with digoxin (Figure). Other novel with- anolides have been isolated and characterized from Ash- wagandha. 2–4 Withanolides also have some structural sim- ilarity with ginsenosides, the active component of Asian ginseng (Panax ginseng). We reported earlier that Asian ginseng interferes with the fluorescence polarization im- munoassay (FPIA) and the microparticle enzyme immu- noassay (MEIA) of digoxin but has no effect on the Beck- man, Roche, or the chemiluminescent assay (Bayer, Tar- rytown, NY). 5,6 Therefore, it was theorized that Ashwa- gandha may affect FPIA and MEIA assessment of digoxin. The possibility also exists that constituents of Ashwagan- dha may interfere with immunoassays of other therapeu- tic drugs. Moreover, herbal products are not prepared fol- lowing rigorous pharmaceutical standard, and compo- nents of a herbal product may vary significantly between