Medicine & USMLE

Diltiazem and Verapamil (Calcium Channel Blockers)

Cardio Drugs - Antiarrhythmics
  1. Diltiazem and Verapamil (Calcium Channel Blockers)
  2. Class 1A Antiarrhythmics
  3. Class 1B Antiarrhythmics
  4. Class 1C Antiarrhythmics
  5. Class 3 Antiarrhythmics
  6. Amiodarone Side Effects
  7. Adenosine


Diltiazem and verapamil are calcium channel blockers that are classified as class 4 antiarrhythmics.

These drugs specifically act as non-dihydropyridine calcium channel blockers. They work in the body by causing vasodilation and slowing down the heart rate. They also weaken the heart’s contractions and slow the electrical conduction through the AV node.

As antiarrhythmics, these drugs are useful in treating arrhythmias with abnormally fast rhythms, such as SVT, A-fib, and atrial flutter. They can also be used to treat angina and myocardial infarctions, as well as hypertension.

Side effects of diltiazem and verapamil include hypotension, constipation, and edema. They can also lead to cardiac complications such as heart block and heart failure. Other side effects to watch for include dizziness, headaches, and bradycardia.

Patients taking calcium channel blockers should avoid grapefruit juice.

Key Points

  • Diltiazem (Cardizem) and Verapamil (Calan)
    • Drug Class
      • Calcium Channel Blockers
        • The movement of calcium plays a crucial role in muscle contraction, nerve signaling, and other cellular functions
        • Non-Dihydropyridine
          • Calcium channel blockers can be separated into two types: the dihydropyridines and the non-dihydropyridines. Diltiazem and verapamil are non-dihydropyridines
      • Class 4 Antiarrhythmics
        • Antiarrhythmic drugs are divided into classes based on their mechanism
    • Mechanism
      • Decrease heart contractility
        • Negative inotrope
        • Reduce the strength of heart muscle contractions, helping to lower blood pressure and improve heart function.
      • Slow conduction through the AV node
        • Slow down the electrical impulses in the heart's atrioventricular (AV) node, regulating heart rate and rhythm.
      • Vasodilation
        • Cause blood vessels to relax and widen, improving blood flow and reducing strain on the heart.
      • Slow heart rate
        • Slowing down the heart rate assists in managing irregular heart rhythms
    • Clinical Use
      • Treat angina (chest pain) and myocardial infarction (MI)
        • Alleviate chest pain by improving blood flow to the heart muscle.
      • Treat hypertension
      • Treat atrial fibrillation
        • An arrhythmia where the atria are contracting quickly and irregularly
      • Treat atrial flutter
        • An arrhythmia where the atria are contracting quickly, but regularly. There are several atrial contractions during the time of one ventricular contraction.
      • Treat supraventricular tachycardia (SVT)
        • An abnormally fast heart rhythm that originates above the ventricles
    • Side Effects
      • Bradycardia
        • Do not give if heart rate is <60 beats per minute
        • Use with caution with beta blockers, since both medications slow the heart rate
      • Heart failure
        • Weakening the heart’s contractility can precipitate heart failure
        • Use with caution in patients with heart failure
      • AV block
        • Caused by the medication slowing the conduction through the AV node
      • Hypotension
        • Carefully monitor patient’s blood pressure during treatment
      • Dizziness (Orthostatic Hypotension)
        • Sudden changes in movement can cause the blood pressure to drop, making the patient feel dizzy
        • Advise patients to change positions slowly to prevent dizziness and falls
      • Edema
        • Fluid and sodium retention lead to swelling in the extremities, especially the legs and ankles
        • Report swelling of the lower extremities to the provider
      • Constipation
        • Increase fluid and fiber intake
      • Headache
    • Nursing Considerations
      • Avoid grapefruit juice
        • Grapefruit juice interferes with how calcium channel blockers are metabolized in the body
        • A buildup of calcium channel blockers in the blood can lead to toxicity