Use of Dietary Supplements by Patients Taking Digoxin

18 Nov
2010

digoxin

INTRODUCTION

Digoxin is commonly used to treat heart failure and atrial fibrillation.0 Its pharmacological effects include increasing the force of myocardial contractions, slowing the heart rate, and reducing the activity of the sympathetic nervous system. Most of the adverse effects of digoxin are dose-dependent, the most common being cardiac side effects, gastrointestinal disturbances, and central nervous system disturbances. Traditionally a therapeutic serum concentration range of 0.8 to 2 ng/mL (1.0 to 2.6 nmol/L) has been suggested, to prevent toxic effects that may occur at higher concentrations. However, recent studies have suggested a lower digoxin concentration range, 0.5 to 0.8 or 0.9 ng/mL (0.6 to 1.0 or 1.2 nmol/L), for treatment efficacy, especially for women with heart failure; in addition, to avoid potential toxic effects, it is now recommended that the serum digoxin level be less than 1.0 ng/mL (1.3 nmol/L) in patients with heart failure. Because digoxin is subject to various drug-drug interactions and because it has a relatively narrow therapeutic index, the dosage should be adjusted according to body weight, age, renal function, concurrent medications, and clinical observations.

Polypharmacy is increasingly common, especially among patients with cardiac diseases. Many patients take multiple prescription and over-the-counter (OTC) medications that could interact, particularly when regimens include agents with a narrow therapeutic index, like digoxin. For example, potassium-depleting diuretics, commonly used for patients with heart failure, can cause hypokalemia, which in turn increases the risk of digoxin toxicity. Macrolide antibiotics and tetracyclines may increase the bioavailability of digoxin, leading to elevated digoxin concentrations. Conversely, antacids and antidiarrheal agents may interfere with absorption of digoxin. In addition, other common medications used by patients with heart disease, such as blockers, nonsteroidal anti-inflammatory drugs, spironolactone, and quinidine, may all lead to digoxin intoxication by elevating the serum concentration of digoxin. cialis professional

In North America, the use of dietary supplements, especially herbal products and vitamins, is increasing. A US survey revealed that the use of herbs by the general public increased from 12% in 1997 to 19% in 2002; however, consultation with a practitioner regarding the use of herbal medicines decreased from 15% to 5% over the same period. In a recent survey by Health Canada, 71% of Canadians surveyed had used a natural health product (including vitamins, minerals, herbal remedies, and teas), and almost 40% of the users reported using natural health products on a daily basis. Wood and others, who surveyed a cohort of patients with cardio­vascular disease in Nova Scotia, found that over 40% of the patients used oral nutritional supplements (herbal or nonherbal or both), and 65% of the supplement users cited their cardiovascular disease as the reason for doing so.

In light of the increased use of dietary supplements, the potential for herb-drug interactions in the context of cardiac disease should be evaluated. The available literature suggests a high potential for interactions between digoxin and dietary supplements, especially herbal products. Some herbal medicines are thought to interfere with digoxin monitoring15 and others with the drug’s pharmacodynamics (by inhibiting or potentiating its effects or by having additive digoxin-like effects). Licorice root (Glycyrrhiza glabra), hawthorn (Crataegus oxyacantha), St John’s wort (Hypericum perfora­tum), Siberian ginseng (Eleutherococcus senticosus) and Ginkgo biloba are examples of herbal medicines for which interactions with digoxin have been suggested. Although the literature on this subject outlines the potential danger of such interactions, there is a lack of studies evaluating the prevalence of dietary supplement use in conjunction with digoxin and the specific types of supplements used by this patient group. It is also unclear whether these interactions translate into clinically relevant adverse effects among patients taking digoxin.
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The objectives of this study were to determine the prevalence of use of nonprescription medications, especially herbal supplements, in a group of patients receiving digoxin therapy and to assess the impact of literature-reported interactions between digoxin and dietary supplements or OTC medications on clinical symptoms commonly associated with digoxin toxicity in an outpatient setting.

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