Diltiazem: Uses, Dosage, Side Effects & Warnings

Introduction to Diltiazem

Diltiazem is a prescription medication used to treat high blood pressure, control angina (chest pain), and manage certain heart rhythm disorders. It belongs to a class of medications called calcium-channel blockers, which work by relaxing blood vessels and reducing the heart’s workload. Diltiazem was first discovered in the 1970s and has since become a widely used medication for various cardiovascular conditions.

Pharmacological Class

Diltiazem is classified as a non-dihydropyridine calcium-channel blocker. It differs from other calcium-channel blockers, such as amlodipine and nifedipine, in its chemical structure and specific effects on the cardiovascular system. Diltiazem is known for its ability to slow heart rate and conduction through the atrioventricular (AV) node, making it useful in treating certain arrhythmias (Chew et al., 1995).

Mechanism of Action

Diltiazem works by blocking calcium channels in the smooth muscle cells of blood vessels and the heart. By reducing calcium influx, diltiazem causes vasodilation (widening of blood vessels) and decreases the force of cardiac muscle contraction. This leads to lower blood pressure, reduced heart rate, and decreased oxygen demand by the heart (Godfraind, 2017).

Therapeutic Uses

Diltiazem is primarily used to treat high blood pressure (hypertension), control angina, and manage certain types of arrhythmias. It is particularly effective in treating stable angina, variant angina (Prinzmetal’s angina), and unstable angina (Hassett, 2020). Diltiazem may also be used to prevent exercise-induced angina attacks and improve exercise tolerance in patients with chronic stable angina.

Dosage Forms and Administration

Diltiazem is available in various oral dosage forms, including tablets, capsules, and extended-release (ER) or sustained-release (SR) formulations. The dosage depends on the specific condition being treated and individual patient factors. Common brand names for diltiazem include Cardizem, Cartia XT, Dilacor XR, Dilt-XR, Diltia XT, and Tiazac. Parenteral (injectable) forms of diltiazem are also available for specific clinical scenarios, such as acute hypertensive emergencies or rapid heart rate control (Fares et al., 2020).

Side Effects

Common side effects of diltiazem include headache, dizziness, fatigue, nausea, and peripheral edema (swelling of the ankles or feet). More serious side effects may include bradycardia (slow heart rate), hypotension (low blood pressure), heart block, and worsening heart failure. Long-term use of diltiazem may be associated with gingival hyperplasia (overgrowth of gum tissue) (Samudrala, 2010).

Drug Interactions

Diltiazem can interact with various medications, including other antihypertensives, beta-blockers, digoxin, and certain antibiotics. Concomitant use of diltiazem with drugs that slow heart rate or conduction, such as beta-blockers or digoxin, may lead to additive effects and increase the risk of bradycardia or heart block. Diltiazem may also increase the blood levels of certain statins, such as simvastatin, potentially increasing the risk of statin-related adverse effects (Godfraind, 2017).

Pharmacokinetics

Diltiazem is well absorbed from the gastrointestinal tract, with an oral bioavailability of approximately 40-60%. It undergoes extensive first-pass metabolism in the liver, primarily by the CYP3A4 enzyme. The elimination half-life of diltiazem ranges from 3 to 7 hours, depending on the formulation. Diltiazem is extensively metabolized, and its metabolites are excreted mainly in the urine (Fares et al., 2020).

Clinical Guidelines and Uses

Clinical guidelines recommend diltiazem as a first-line or alternative treatment option for various cardiovascular conditions. The American Heart Association and American College of Cardiology (AHA/ACC) guidelines recommend diltiazem as a first-line agent for the treatment of stable ischemic heart disease and vasospastic angina (Knuuti et al., 2020). The Joint National Committee (JNC) 8 guidelines suggest diltiazem as an alternative antihypertensive agent in specific patient populations, such as those with chronic kidney disease or diabetes (James et al., 2014).

Contraindications and Precautions

Diltiazem is contraindicated in patients with known hypersensitivity to the drug, sick sinus syndrome, second- or third-degree AV block (unless a functioning pacemaker is present), and severe hypotension (systolic blood pressure < 90 mmHg). Diltiazem should be used with caution in patients with heart failure, bradycardia, or impaired renal or hepatic function. Pregnant women should use diltiazem only if the potential benefit justifies the potential risk to the fetus, as safety during pregnancy has not been established. Nursing mothers should also exercise caution, as diltiazem is excreted in human milk (Fares et al., 2020).