Summary

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

Introduction

Diltiazem is a calcium channel blocker commonly prescribed for hypertension, angina, and certain heart rhythm disorders. It works by relaxing blood vessels and reducing heart rate. Digoxin is a cardiac glycoside used to treat heart failure and atrial fibrillation by increasing the strength of heart contractions and controlling heart rate. Both medications are frequently prescribed for cardiovascular conditions, making their potential interaction clinically significant.

Mechanism of Interaction

Diltiazem inhibits P-glycoprotein, a transport protein responsible for eliminating digoxin from the body through the kidneys and intestines. When diltiazem blocks this elimination pathway, digoxin accumulates in the bloodstream, leading to elevated serum digoxin concentrations. This pharmacokinetic interaction can increase digoxin levels by 20-50%, significantly raising the risk of digoxin toxicity even at previously therapeutic doses.

Risks and Symptoms

The primary risk of this interaction is digoxin toxicity, which can be life-threatening. Symptoms include nausea, vomiting, loss of appetite, confusion, visual disturbances (yellow or green halos), 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 due to reduced digoxin clearance. The narrow therapeutic window of digoxin makes even modest increases in blood levels potentially dangerous.

Management and Precautions

When diltiazem and digoxin must be used together, reduce the digoxin dose by 25-50% and monitor serum digoxin levels closely. Check digoxin levels within 1-2 weeks of starting diltiazem or changing doses. Monitor patients for signs of digoxin toxicity including gastrointestinal symptoms, neurological changes, and cardiac arrhythmias. Regular ECG monitoring and electrolyte assessment (especially potassium and magnesium) are essential. Consider alternative calcium channel blockers with less P-glycoprotein inhibition if clinically appropriate. Always consult with a healthcare professional before making any medication adjustments.

Diltiazem interactions with food and lifestyle

Grapefruit and grapefruit juice should be avoided while taking diltiazem as they can significantly increase blood levels of the medication, potentially leading to dangerous drops in blood pressure and heart rate. Alcohol consumption should be limited or avoided as it can enhance the blood pressure-lowering effects of diltiazem and increase the risk of dizziness, fainting, and falls. Patients should also be cautious when standing up quickly or engaging in activities requiring alertness, as diltiazem can cause dizziness and lightheadedness, especially when starting treatment or increasing the dose.

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.