Digoxin-Chan Su interaction

Ingestion of Chan Su, a Chinese topical anesthetic and purported aphrodisiac, has been known to cause a dangerous, acute reaction similar to digoxin toxicity.
By John Russo Jr./Vicus.com

VICUS.COM (14 Aug. 2000) — Certain laboratory tests used to measure the concentration of digoxin in blood cannot distinguish between digoxin and Chan Su, according to research published by Amitava Dasgupta, Ph.D., and colleagues at the University of Texas-Houston Medical School.

The results may inaccurately indicate higher or lower digoxin blood concentrations because of interference by ingredients in Chan Su such as bufalin, cinobufagin and reibufogenin, which have similar molecular structures to digoxin. Adding to the confusion, other testing procedures are not altered by Chan Su (Dasgupta,  et al., 2000).

Chan Su toxicity

Chan Su as a topical anesthetic prepared from the skin of the Chinese toad  Bufo bufo gargarizans Gantor (or Bufo melanostictus). It is also used as an aphrodisiac and sold under the name, “Love Stone,” “Black Stone,” “Stone” and “Rock Hard.” Several years ago, the New York City Poison Control Center reported four men who died from cardiac dysrhythmias (abnormal heartbeats). Each person had measurable levels of “digoxin” in their serum. However, digoxin had not been prescribed for them.

Symptoms of toxicity

A health-care provider or an emergency department should be contacted if any of the following symptoms occur while using Chan Su. These are common symptoms of toxicity from digitalis glycosides such as digoxin or digitalis. They may also occur with Chan Su because it also contains cardioactive substances:

  • Diarrhea

  • Drowsiness or sleepiness
  • Loss of appetite
  • Muscle weakness
  • Nausea Vomiting
  • Yellow vision (xanthopsia)

The acute reaction after taking Chan Su can be similar to what is seen in a person who  experiences digoxin toxicity. The heart beats abnormally and death can occur fairly rapidly, within a day of taking the tablet. 

For example, a 26-year-old man began to vomit several hours after swallowing one piece of the topical aphrodisiac. He also felt weak and complained of stomach pain. When he sought medical care at an emergency department about 16 hours after taking Chan Su, his blood pressure was low (94/60 mm Hg) and his heart rate was rapid (90 beats per minute). 

A blood sample was taken to the laboratory where it was found that his serum potassium was 8.4 mEq/L (normal: 3.5-5.0 mEq/L) and serum bicarbonate was 18 mEq/L (normal: 22-28 mEq/L). His serum creatinine was 3.2 mg/dL (normal: 0.6-1.2 mg/dL), suggesting poor kidney function, and his blood glucose level was of 164 mg/dL (normal: 70-110 mg/dL).

Over time, his heart rhythm became unstable, changing from a normal rhythm to atrial fibrillation (a rapid twitching of the upper portion of the heart) to bradycardia (an abnormal slowing of the heart rate). Eventually, his heart rhythm changed to ventricular fibrillation (a rapid twitching of the lower portion of the heart), and he died from cardiac arrest seven hours after admission to the emergency department, approximately 20 hours after ingesting the aphrodisiac. A blood sample revealed toxic levels of digoxin in his body (2.8 ng/mL; normal = 0 ng/mL). Yet, this person had never taken digoxin (MMWR, 1995).


The report by Dasgupta provides good reason for people who are being treated with digoxin or other digitalis glycosides to inform their health-care provider that they are also using Chan Su. However, it raises several other issues related to the safe use of Chan Su.

The case history presented here is an extreme example of a toxic reaction to Chan Su. The presentation is similar to what might be seen in a patient experiencing extreme digoxin toxicity. People being treated with digoxin and also taking Chan Su should be aware that in addition to causing erroneous results in the serum digoxin test, the combined use of these drugs can lead to additive toxic effects.

In addition, many people who do not take digoxin are using Chan Su to treat conditions such as tonsillitis, sore throat, furuncle (boil) and palpitations. When used as a topical pain reliever or to control fluttering in the chest, subtle adverse reactions may occur.  

John Russo Jr, PharmD, is senior vice president of medical communications at Vicus.com. He is a pharmacist and medical writer with more than 20 years of experience in medical education.


Brubacher JR, Ravikumar PR, Bania T, et al. Treatment of toad venom poisoning with digoxin-specific Fab fragments. Chest. 1996 Nov; 110(5):1282-8.

Dasgupta A, Biddle DA, Wells A, et al. Positive and negative interference of the Chinese medicine Chan Su in serum digoxin measurement. Am J Clin Pathol.  2000 Aug; 114(2):174-9.

Datta P, Dasgupta A. Interactions between drugs and Asian medicine: displacement of digitoxin from protein binding site by bufalin, the constituent of Chinese medicines Chan Su and Lu-Shen-Wan. Ther Drug Monit. 2000 Apr; 22(2):155-9.

Morbidity and Mortality Weekly Report. Deaths Associated with a Purported Aphrodisiac — New York City, Feb. 1993-May 1995. MMWR Weekly. 24 Nov. 1995; 44(46);853-855, 861.  http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/00039633.htm