Summary

Erythromycin significantly increases digoxin blood levels by inhibiting its metabolism and transport, potentially leading to digoxin toxicity. This interaction requires careful monitoring and possible dose adjustments when these medications are used together.

Introduction

Erythromycin is a macrolide antibiotic commonly prescribed to treat bacterial infections including respiratory tract infections, skin infections, and sexually transmitted diseases. Digoxin is a cardiac glycoside medication used to treat heart failure and certain heart rhythm disorders by increasing the strength of heart contractions and controlling heart rate. Both medications are frequently prescribed, making their potential interaction clinically significant.

Mechanism of Interaction

Erythromycin increases digoxin plasma concentrations through multiple mechanisms. The primary mechanism involves inhibition of P-glycoprotein, a transport protein responsible for digoxin elimination from cells and tissues. Erythromycin also inhibits cytochrome P450 enzymes and may reduce digoxin clearance by the kidneys. Additionally, erythromycin can alter gut bacteria that normally metabolize digoxin, leading to increased absorption of the unchanged drug. These combined effects can result in digoxin levels increasing by 50-100% or more.

Risks and Symptoms

The primary risk of this interaction is digoxin toxicity, which can be life-threatening. Signs and symptoms of digoxin toxicity include nausea, vomiting, loss of appetite, visual disturbances (yellow or green halos around lights), confusion, and dangerous heart rhythm abnormalities such as bradycardia, heart block, or ventricular arrhythmias. Elderly patients and those with kidney disease are at particularly high risk. The interaction typically begins within 24-48 hours of starting erythromycin and can persist for several days after discontinuation due to digoxin's long half-life.

Management and Precautions

When erythromycin and digoxin must be used together, close monitoring is essential. Digoxin levels should be checked before starting erythromycin and again 3-5 days after initiation. Consider reducing the digoxin dose by 25-50% when starting erythromycin. Monitor patients closely for signs of digoxin toxicity including heart rate, rhythm, and clinical symptoms. Alternative antibiotics such as azithromycin or fluoroquinolones may be considered if clinically appropriate. If erythromycin is discontinued, digoxin levels may decrease, requiring dose readjustment. Regular monitoring of electrolytes, particularly potassium and magnesium, is also important as imbalances can increase digoxin toxicity risk.

Erythromycin interactions with food and lifestyle

Erythromycin should be taken on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption, as food can significantly reduce the drug's bioavailability. However, if gastrointestinal upset occurs, it may be taken with food to minimize stomach irritation, though this may reduce effectiveness. Alcohol consumption should be avoided or limited while taking erythromycin, as it may increase the risk of gastrointestinal side effects and potentially reduce the antibiotic's effectiveness. Patients should also avoid taking erythromycin with dairy products or calcium-fortified foods within 2 hours of dosing, as calcium can interfere with absorption.

Digoxin interactions with food and lifestyle

Digoxin has several important food and lifestyle interactions that patients should be aware of. High-fiber foods, including bran cereals and fiber supplements, can significantly reduce digoxin absorption and should be taken at least 2 hours apart from digoxin doses. St. John's wort, an herbal supplement, can decrease digoxin levels and reduce its effectiveness, so concurrent use should be avoided. Alcohol consumption can affect digoxin levels and increase the risk of side effects, particularly heart rhythm abnormalities. Patients should limit alcohol intake and discuss any alcohol use with their healthcare provider. Additionally, maintaining consistent dietary habits is important, as sudden changes in fiber intake or meal timing can affect digoxin absorption and blood levels. Patients should also be cautious with salt substitutes containing potassium, as changes in potassium levels can affect digoxin's effectiveness and safety.