Which foods and medications interact with digoxin?

Digoxin Drug and Food Interactions

Reduce digoxin dose by 30-50% when initiating amiodarone or dronedarone, and monitor digoxin levels closely when starting clarithromycin, erythromycin, itraconazole, cyclosporine, propafenone, verapamil, or quinidine, as these medications significantly increase serum digoxin concentrations and toxicity risk. 1

Major Drug Interactions Requiring Dose Adjustment

P-glycoprotein Inhibitors (Most Clinically Significant)

The following medications increase digoxin levels by inhibiting P-glycoprotein transport and require proactive management:

Require Dose Reduction:

• Dronedarone: Reduce digoxin dose by at least 50% 2
• Amiodarone: Reduce digoxin dose by 30-50% 2

Require Close Monitoring of Digoxin Levels:

• Verapamil
• Clarithromycin
• Cyclosporine
• Erythromycin
• Flecainide
• Itraconazole
• Posaconazole
• Propafenone
• Voriconazole 2

Additional P-glycoprotein Substrates:

• Quinidine (classic interaction, increases digoxin levels significantly) 1, 3, 1

Other Significant Drug Interactions

Antibiotics that increase digoxin bioavailability (in patients who metabolize digoxin via gut bacteria - approximately 10% of patients):

• Erythromycin
• Clarithromycin
• Tetracycline 1, 4

These antibiotics kill colonic bacteria that normally inactivate digoxin, potentially doubling serum concentrations in susceptible patients. The rise occurs gradually over days, consistent with digoxin's elimination half-life.

Medications that decrease digoxin absorption:

• Antacids (aluminum hydroxide, magnesium hydroxide, magnesium trisilicate)
• Kaolin-pectin
• Cholestyramine
• Sulfasalazine
• Neomycin
• Metoclopramide (decreases absorption by increasing gut motility) 4, 5

Rifampin: Decreases serum digoxin concentration by increasing non-renal clearance, particularly problematic in patients with renal dysfunction 4

Food Interactions

High-Fiber Foods (Bran)

Bran fiber reduces digoxin absorption by 6-7% when taken concurrently 6. While this reduction is modest and likely clinically unimportant for most patients, it can contribute to subtherapeutic levels in borderline cases. The effect is less pronounced with digoxin capsules compared to tablets.

Standard Meals

Food decreases the rate but not the extent of digoxin absorption 7. Peak plasma concentrations are lower when digoxin is taken with food (2.8 ng/mL) versus fasting (4.2 ng/mL), but total absorption (AUC) remains unchanged. This is clinically insignificant for chronic therapy but may delay onset of effect in acute situations.

Grapefruit Juice

Grapefruit juice has minimal clinical effect on digoxin pharmacokinetics 8. Despite theoretical concerns about P-glycoprotein inhibition, studies show only a 9% increase in early digoxin AUC with no significant change in overall bioavailability or renal clearance.

Electrolyte and Metabolic Interactions

Critical factors that increase digoxin toxicity risk even at therapeutic levels:

• Hypokalemia (most important - potassium-depleting diuretics are a major contributor to toxicity) 1, 3, 1
• Hypomagnesemia 1, 3, 1
• Hypothyroidism 1, 3, 1
• Hypercalcemia (IV calcium can produce serious arrhythmias in digitalized patients) 4

Maintain serum potassium ≥4.0 mmol/L in patients on digoxin 9.

Additional Interactions Requiring Caution

Sympathomimetics: Increase risk of cardiac arrhythmias when combined with digoxin 4

Succinylcholine: May cause sudden potassium extrusion from muscle cells, precipitating arrhythmias in digitalized patients 4

Beta-blockers and calcium channel blockers: While useful for rate control in atrial fibrillation, additive AV nodal effects can cause advanced or complete heart block 4

Thyroid hormone: Administration to a digitalized hypothyroid patient may increase digoxin dose requirements 4

Clinical Monitoring Strategy

Monitor digoxin levels when:

• Initiating any of the above interacting medications
• During dehydrating illness
• With increases in digoxin or diuretic doses
• Checking electrolytes (potassium, magnesium) and renal function 9

Target therapeutic range: 0.5-0.9 ng/mL for heart failure, as levels >1.0 ng/mL are associated with increased mortality without superior outcomes 1.

Common Pitfalls

1. Failing to reduce digoxin dose preemptively when starting amiodarone or dronedarone - toxicity will develop gradually
2. Not recognizing the 10% of patients who metabolize digoxin via gut bacteria and are susceptible to antibiotic interactions
3. Overlooking electrolyte abnormalities as contributors to toxicity at "therapeutic" levels
4. Using outdated therapeutic ranges (0.8-2.0 ng/mL) rather than current evidence-based targets (0.5-0.9 ng/mL)