St. John’s wort and digoxin – a possible dangerous duo

The interaction between St. John’s wort and digoxin is complex, with potentially serious consequences.

By John Russo Jr./Vicus.com

Despite these sales figures — culled from HerbalGram, the journal of the American Botanical Council and the Herb Research Foundation, and the Nutrition Business Journal — it is becoming well-established in the literature that St. John’s wort can reduce the effectiveness of or interact negatively with many prescription drugs when taken concurrently.  

One of these interacting drugs is digoxin, which is commonly prescribed for patients with congestive heart failure (Kothari, 1997). The drug is used to strengthen the contraction of the heart muscle, slow the heart rate and promote the elimination of fluid from body tissues.  Almost 5 million Americans are living with CHF, according to the American Heart Association, and the condition has become the single most expensive health-care item in the United States and the No. 1 hospital-discharge diagnosis in the elderly (Schrier, et al., 2000).

Digoxin is one of the oldest and most widely prescribed drugs in medicine, with a lineage that rivals St. John’s wort. Digoxin is derived from Digitalis lanata or Digitalis purpurea (also known as the foxglove plant) and has been used medicinally since the days of the ancient Egyptians and the Roman Empire. 

Digoxin has been a mainstay of modern medicine during this century. But its value, particularly for heart failure, has been hotly debated, especially during the past two decades, as newer, more effective drugs have become available, and clinical trials in heart failure have failed to confirm the value of digoxin beyond a doubt (Garg, et al., 1997; Kothari, 1997; Van Veldhuisen, et al., 1997). 

St. John’s wort has been shown to lower the blood levels and, subsequently, the therapeutic effects of digoxin, as well as many other medications (Baede-van Dijk, et al., 2000; Fugh-Berman, 2000; Johne, et al., 1999). 

There are three scenarios in which this interaction can have important consequences.

• Scenario 1. You add St. John’s wort to digoxin therapy: If you are already taking digoxin for heart failure or abnormal heart rhythms and are getting a good response, adding St. John’s wort will result in lower digoxin levels.What could happen: You may find that you are not responding well to the digoxin and symptoms from your heart condition are returning (e.g., breathlessness, swollen ankles and weakness).
• Scenario 2. You stop taking St. John’s wort but keep taking digoxin: Any time you stop taking St. John’s wort, but continue to take digoxin, your digoxin levels may go up.What could happen: This unintended increase in digoxin blood concentrations may lead to digoxin toxicity. You could experience abnormal heartbeats, visual disturbances (“halo,” “yellow” or “snowy” vision), lethargy and fatigue, and intestinal symptoms (anorexia, nausea and diarrhea). Other common signs of digoxin toxicity are crying, agitation, hallucinations, nightmares, paranoia, drowsiness and confusion.
• Scenario 3. You take St. John’s wort occasionally: If you take St. John’s wort only when you are feeling “down,” and then stop it when you feel better, your digoxin blood levels will fluctuate each time you start or stop St. John’s wort.What could happen: If your blood digoxin level gets too low (after you start taking St. John’s wort), there may be a loss of effectiveness and a return of the symptoms of heart disease. If the blood levels increase too much, it could lead to digoxin toxicity.

What’s a patient to do?

The interaction between St. John’s wort and digoxin is complex, with potentially serious consequences. Speak with your health practitioner if you are already taking either drug and if you think you might want to take them together. Know the signs and symptoms associated with digoxin blood levels that are too low or too high.

John Russo Jr., Pharm.D., 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.

References:

American Heart Association: Cardiovascular diseases prevalence
http://www..americanheart.org/statistics/03cardio.html

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