A Closer Look at Heart Medication Verapamil

Heart on a plate
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Verapamil is a potent medication used to treat heart disease. Because it dilates the blood vessels of the heart and body both, it has numerous clinical applications. But in addition to having many uses, your dosage of verapamil needs to be closely monitored because this medication poses toxicity risk and can have serious adverse effects. For example, accidental ingestion of one tablet by a child can lethal.

Mechanism of Action

Verapamil is a calcium-channel blocker (antagonist) which decreases the entry of calcium ions through L-type calcium channels located in heart cells and smooth muscle cells of the peripheral vasculature.

Verapamil has numerous physiologic effects:

  • Vasodilation of both coronary (heart) and peripheral arteries and arterioles
  • Decreased cardiac contractility
  • Depressed sinus node activity
  • Slowed atrioventricular node conduction

In addition to the above effects, verapamil also interferes with the energy metabolism of cardiac cells, increasing the heart's dependence on carbohydrates rather than free fatty acids. Moreover, verapamil inhibits pancreatic production of insulin. These two toxic changes become particularly pronounced in cases of shock when the body needs carbohydrates.

Metabolism

Verapamil is well absorbed via the gastrointestinal tract and distributes widely throughout the body (90 percent protein bound).

On the first-pass metabolism, verapamil is broken down by the liver into an active metabolite. Verapamil's half-life is about eight hours.

Clinical Uses

Because of its effects on both heart and body vasculature (blood vessel), verapamil has an array of uses. Here are some of verapamil's uses:

  • Angina (stable, unstable and Prinzmetal's)

Verapamil is a class-IV antiarrhythmic drug. Before physicians used verapamil to treat arrhythmias, propranolol and digoxin were often used.

Adverse Effects and Drug Interactions

Although rare under the close monitoring of a cardiologist, verapamil toxicity is always a concern. In addition to its own adverse effects, verapamil can also interact with a wide variety of other drugs.

The most frequent adverse effect of verapamil is constipation. In some people, verapamil can cause dizziness, light-headedness, and hypotension. In cases of overdose, verapamil interferes with the rhythm of the heart and can lead to loss of life.

Here are some of the drug-drug interactions that verapamil poses:

  • Verapamil uses with beta-blockers, nitrates and diuretics blood pressure can cause your blood pressure to fall dangerously low (hypotension).
  • Verapamil can increase the effect of statins, which are used to treat high cholesterol, and statins can cause rhabdomyolysis or muscle breakdown which screws with the kidneys.
  • Verapamil is metabolized by the cytochrome P450 enzymes and concomitant use of prescription medications like amiodarone (another antiarrhythmic) interferes with P450 leading to verapamil toxicity. Additionally, grapefruit juice also affects the P450 system and may increase verapamil blood concentrations.

    Please keep in mind that when used as advised and in a safe manner, verapamil can be of great benefit to those who need it. The information in this article is not meant to scare you from using verapamil when advised. However, you must closely heed your cardiologist's advice while using this, or any other, medication.

    If you or a loved one is taking verapamil, it's imperative that you are closely monitored by your prescribing cardiologist. Make appointments for regular check-ups with your cardiologist and be sure to inform your physician of any changes in medication regimen including any use of herbal medications.

    Furthermore, if you are feeling any adverse effects that may be attributable to verapamil like fainting or temporary loss of consciousness, call for emergency help.

    Sources:

    Lynch, T and Price, A. "The Effect of Cytochrome P450 Metabolism on Drug Response, Interactions, and Adverse Effects" American Family Physician. 2007.

    Mosby's Drug Reference for Health Professions, Second Edition. Elsevier. 2010.

    Tomaszewski CA, Benowitz NL. Chapter 40. Calcium Channel Antagonists. In: Olson KR. eds. Poisoning & Drug Overdose, 6e. New York, NY: McGraw-Hill; 2012.