Understanding How Diltiazem Works
As a non-dihydropyridine calcium channel blocker (CCB), diltiazem exerts its therapeutic effects by inhibiting the influx of calcium ions into cardiac muscle cells and vascular smooth muscle cells. Calcium is essential for muscle contraction, so blocking its entry causes these muscles to relax. This mechanism is responsible for diltiazem's wide-ranging cardiovascular effects.
How Diltiazem Affects the Heart
By inhibiting calcium's entry, diltiazem has several key effects on the heart and circulatory system:
- Relaxation of blood vessels: The drug causes the vascular smooth muscles to relax, resulting in vasodilation (widening of blood vessels) and a decrease in peripheral vascular resistance. This is the primary way it lowers blood pressure.
- Reduced heart rate: Diltiazem slows the heart rate by acting on the heart's conduction system, specifically the sinoatrial (SA) and atrioventricular (AV) nodes. This reduces the number of electrical impulses passing through the heart, decreasing heart rate.
- Decreased heart muscle contraction: It acts as a negative inotrope, reducing the force of the heart's contractions.
- Increased oxygen supply: By widening the coronary arteries, diltiazem increases the flow of blood and oxygen to the heart muscle, a key benefit for angina patients.
Primary Uses of Diltiazem
Diltiazem is a versatile medication with several FDA-approved and off-label uses for managing cardiovascular conditions.
Hypertension (High Blood Pressure)
Diltiazem is widely used to treat high blood pressure, or hypertension, either alone or in combination with other medications. The relaxation of blood vessels reduces the heart's workload, helping to protect organs like the brain, heart, and kidneys from long-term damage caused by high blood pressure. It is important for patients to continue taking the medication even if they feel well, as hypertension often has no obvious symptoms.
Angina (Chest Pain)
For patients with chronic stable angina or angina due to coronary artery spasms, diltiazem is used to prevent chest pain. By increasing the heart's blood and oxygen supply while reducing its workload, it can reduce the frequency and severity of anginal episodes. It is important to note that diltiazem helps prevent chest pain but does not stop it once it has started; a different medication is needed for acute attacks.
Cardiac Arrhythmias
Diltiazem is used to control certain types of abnormal heart rhythms, known as arrhythmias, particularly supraventricular tachycardias (SVT).
- Atrial Fibrillation and Flutter: It is used for rate control in atrial fibrillation (AFib) and flutter with a rapid ventricular response, slowing the heart rate and allowing for more efficient heart function.
- Paroxysmal Supraventricular Tachycardia (PSVT): An intravenous form of diltiazem is used for the rapid conversion of PSVT that is unresponsive to initial treatments like vagal maneuvers and adenosine.
Other Uses
While primarily used for the heart, diltiazem has other, sometimes off-label, uses:
- Raynaud's phenomenon: It helps to relax and widen blood vessels in the fingers and toes, improving blood flow and reducing attacks.
- Anal fissures: As a topical cream or ointment, diltiazem can help heal tears in the anus by relaxing the muscle and increasing blood flow to the area.
Dosage Forms and Administration
Diltiazem comes in various formulations, and understanding the differences is crucial for proper administration.
Oral Formulations:
- Immediate-Release (IR) tablets: Typically taken multiple times a day.
- Extended-Release (ER) capsules and tablets: Taken once or twice daily for a prolonged effect, which is convenient for long-term management of conditions like hypertension.
- Controlled-Release (CD, LA, XR) capsules and tablets: These specialized extended-release forms are designed for once-daily dosing.
Intravenous (IV) Administration:
- An injectable form of diltiazem is used in a hospital setting for rapid treatment of arrhythmias.
Comparison of Diltiazem with Common Alternatives
Different types of medications can treat similar cardiovascular conditions. Here is a comparison of diltiazem with some common alternatives.
| Feature | Diltiazem (Non-Dihydropyridine CCB) | Metoprolol (Beta-Blocker) | Lisinopril (ACE Inhibitor) |
|---|---|---|---|
| Mechanism | Blocks calcium channels in heart muscle and blood vessel walls, relaxing blood vessels and slowing heart rate. | Blocks beta receptors, slowing heart rate and reducing the force of heart contractions. | Prevents production of angiotensin II, relaxing blood vessels and lowering blood pressure. |
| Effect on Heart Rate | Can cause a significant reduction in heart rate. | Causes a reduction in heart rate. | No direct effect on heart rate. |
| Effect on Blood Vessels | Causes vasodilation, reducing peripheral resistance. | Causes some vasodilation, but less directly than CCBs. | Causes vasodilation by blocking angiotensin II. |
| Best for Patients with... | Hypertension, angina, AFib with normal heart function. | Heart failure (HFrEF), hypertension, angina, post-MI. | Hypertension, heart failure, post-MI, kidney disease in diabetics. |
| Key Side Effects | Dizziness, swelling (edema), constipation, headache. | Fatigue, dizziness, depression, bradycardia. | Dry cough, dizziness, headache, high potassium. |
| Common Contraindications | Sick sinus syndrome (without pacemaker), second- or third-degree AV block, severe hypotension, HFrEF. | Severe bradycardia, heart block, severe hypotension. | Pregnancy, angioedema history. |
Potential Side Effects and Contraindications
Like any medication, diltiazem can cause side effects. Many are mild and resolve over time, but some can be serious.
Common Side Effects:
- Dizziness or lightheadedness
- Headache
- Edema (swelling of ankles, feet, or hands)
- Constipation
- Flushing
- Nausea
Serious Side Effects:
- Severe skin reactions, including Stevens-Johnson syndrome
- Liver damage (yellowing of skin or eyes, abdominal pain)
- Worsening heart failure in those with pre-existing impaired ventricular function
- Significant bradycardia (abnormally slow heart rate) or heart block
Contraindications: Diltiazem should not be used in certain conditions:
- Sick Sinus Syndrome or Second-/Third-Degree AV Block: Unless the patient has a functioning ventricular pacemaker, as diltiazem can further slow the heart rate and conduction.
- Severe Hypotension: In cases of very low blood pressure.
- Acute Myocardial Infarction (Heart Attack) with Pulmonary Congestion: In this specific situation, diltiazem is contraindicated.
- Heart Failure with Reduced Ejection Fraction (HFrEF): As diltiazem can further weaken heart contractions.
Conclusion
Diltiazem is an effective and versatile calcium channel blocker with a well-established role in treating a range of cardiovascular conditions, including hypertension, angina, and various arrhythmias. Its ability to relax blood vessels and control heart rate makes it a valuable tool, but its use requires careful consideration of the patient's specific cardiac health, including the presence of heart failure or conduction abnormalities. Patients should have a full discussion with their healthcare provider to ensure it is the most appropriate treatment option for their condition.
For further information, consult the National Institutes of Health (NIH) StatPearls entry on Diltiazem.
