The digitalis drugs digoxin and digitoxin are used for congestive heart failure and other heart conditions. The concerns described below apply equally to both medications.
Magnesium deficiency can increase the risk of toxicity from digoxin. 12 However, taking magnesium supplements at the same time as digoxin might impair the absorption of the drug. 5 The solution? Do not take your magnesium supplement during the two hours before or after your digoxin dose.
Although the evidence is quite weak, digoxin might cause a tendency toward calcium deficiency. 6 Taking calcium supplements could not hurt.
The herb hawthorn is used to treat congestive heart failure. Whether it is safe to combine hawthorn with digoxin remains unclear. One small study failed to find any harmful interaction, but more research must be done before reliable conclusions can be drawn. 16 .
Licorice root can lower potassium levels in the body, which can be dangerous for an individual taking digoxin. 7,8 The special form of licorice known as DGL (deglycyrrhizinated licorice) is a deliberately altered form of the herb that should not affect potassium levels.
There has been one report of an apparent elevation in digoxin level caused by the herb Eleutherococcus senticosus (so-called "Siberian ginseng"). 9 However, the details of the case suggest that the eleutherococcus product might actually have interfered with a test for digoxin, rather than the digoxin levels themselves.
Because horsetail can deplete the body of potassium, it may not be safe to combine this herb with digitalis drugs. 10
Evidence suggests that St. John's wort may interact with digoxin, possibly requiring an increased dosage to maintain the proper effect. 11-13,17 Conversely, if you are taking St. John's wort already and your physician adjusts your dose of medication, suddenly stopping the herb could cause blood levels of the drug to rise dangerously high.
Uzara root ( Xysmalobium undulatum ) is used to treat diarrhea. It contains substances similar to digoxin, and may cause false readings on tests designed to measure digoxin levels. 14 These substances also might alter (either increase or decrease) the effectiveness of digoxin.
One study found that simulataneous use of the herb Ginkgo biloba (80 mg three times daily of the typical standardized extract) does not change digoxin levels. 15
References
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REF2 Whang R, Oei TO, Watanabe A. Frequency of hypomagnesemia in hospitalized patients receiving digitalis. Arch Intern Med . 145: 655656, 1985.
REF3 Landauer RA. Magnesium deficiency and digitalis toxicity. JAMA . 251: 730, 1984.
REF4 Cohen L and Kitzes R. Letter. JAMA . 251: 730, 1984.
REF5 Tatro D (ed.). Drug interaction facts. St. Louis, MO: Facts and Comparisons, 1999: 446.
REF6 Kupfer S and Kosovsky JD. Effects of cardiac glycosides on renal tubular transport of calcium, magnesium, inorganic phosphate and glucose in the dog. J Clin Invest . 44: 11321143, 1965.
REF7 Shintani S, Murase H, Tsukagoshi H, and Shiigai T. Glycyrrhizin (licorice)-induced hypokalemic myopathy. Report of two cases and review of the literature. Eur Neurol . 32: 4451, 1992.
REF8 Pronsky Z (ed.). Powers and Moore's food medication interactions, 10th ed. Pottstown, PA: Food-Medication Interactions, 1997: 49.
REF9 McRae S. Elevated serum digoxin levels in a patient taking digoxin and Siberian ginseng. Can Med Assoc J .155: 293295, 1996.
REF10 Brinker F. Herb contraindications and drug interactions, 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998: 85.
REF11 Maurer A, et al. Interaction of St. John's wort extract with phenprocoumon. Eur J Clin Pharmacol . 55(Abstract 79): A22, 1999.
REF12 Yue QY, Bergquist C, Gerden B. Safety of St. John's wort ( Hypericum perforatum ) [letter]. Lancet . 355: 576577, 2000.
REF13 Mueller SC, Uehleke B, Woehling H, et al. Effect of St John's wort dose and preparations on the pharmacokinetics of digoxin. Clin Pharmacol Ther . 2004;75:546-57.
REF14 Thurmann PA, Neff A, Fleisch J, et al. Interference of Uzara glycosides in assays of digitalis glycosides. Int J Clin Pharmacol Ther . 2004;42:281-4.
REF15 Mauro VF, Mauro LS, Kleshinski JF, et al. Impact of Ginkgo biloba on the pharmacokinetics of digoxin. Am J Ther . 2003;10:247-51.
REF16 Tankanow R, Tamer HR, Streetman DS, et al. Interaction study between digoxin and a preparation of hawthorn (Crataegus oxyacantha). J Clin Pharmacol . 2003;43:637-42.
REF17 Gurley BJ, Swain A, Williams DK, et al. Gauging the clinical significance of P-glycoprotein-mediated herb-drug interactions: Comparative effects of St. John's wort, echinacea, clarithromycin, and rifampin on digoxin pharmacokinetics. Mol Nutr Food Res. 2008 Jan 23.