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Verapamil: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on March 17, 2021.

1. How it works

  • Verapamil affects the passage of calcium ions across cell membranes of smooth muscle cells and heart (myocardial) cells.
  • When used to treat angina, verapamil dilates the main coronary blood vessels and reduces how much energy and oxygen the heart uses to beat.
  • When used to treat arrhythmias, such as Atrial Fibrillation, verapamil prolongs the refractory period (the period immediately following electrical stimulation of the AV node) and slows the heart rate.
  • Verapamil can also lower blood pressure.
  • Verapamil belongs to the class of drugs known as calcium channel blockers.

2. Upsides

  • May be used as an ongoing treatment to relieve symptoms such as chest pain in people with unstable or chronic stable angina, or angina due to coronary artery spasm. Will not relieve acute episodes of angina (other medications such as sublingual nitroglycerin are used for this purpose).
  • May be used to treat certain arrhythmias such as atrial fibrillation, atrial flutter, and repetitive paroxysmal supraventricular tachycardia.
  • May be used for the treatment of high blood pressure (hypertension), alone or in combination with other agents for high blood pressure.
  • Available as immediate-release tablets, extended/sustained-release tablets, and capsules, and in an injectable form.
  • Available as 40mg, 80mg, and 120mg tablets.
  • Generic verapamil is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Constipation, dizziness, headache, facial flushing, nausea, low blood pressure, edema, elevated liver enzymes, sexual dysfunction, and shortness of breath. May also cause cold-like symptoms such as a stuffy nose, sinus pain, and sore throat.
  • May not be suitable for some people including those with certain preexisting heart conditions including severe heart failure, hypotension, sick sinus syndrome, second or third-degree AV block, or those with AF or atrial flutter with an accessory pathway (such as Wolff-Parkinson-White syndrome). Do not use it in people with previous hypersensitivity to verapamil.
  • Severe liver dysfunction prolongs the half-life of verapamil to about 14-16 hours. Reduce dosage to 30% of normal.
  • Administer cautiously to people with kidney disease; monitor for abnormal prolongation of the PR interval. May need extra monitoring or reduce dosage.
  • May cause a worsening of myasthenia gravis and decrease neuromuscular transmission in those with Duchenne's muscular dystrophy. Consider a dosage reduction.
  • May cause elevations in liver transaminases, with or elevations in alkaline phosphatase or bilirubin. Periodically monitor liver enzymes.
  • Metabolized by several cytochrome P450 enzymes: CYP3A4, CYP1A2, CYP2C8, CYP2C9, and CYP 2C18. May interact with several medications including some anti-infectives, tuberculosis medications, other drugs to manage blood pressure or arrhythmias, statins, and grapefruit products.
  • Verapamil is not FDA approved for people younger than 18 years.
  • There is not enough data concerning the effects of verapamil on a developing fetus or the newborn while breastfeeding. Advise women not to become pregnant or breastfeed while taking verapamil.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Verapamil can help regulate the heart rate and lower blood pressure and is used to treat certain heart conditions. Constipation is the most common side effect of verapamil and it may interact with several medicines and grapefruit products.

5. Tips

  • Do not crush, break or chew extended or sustained-release verapamil tablets or capsules; swallow whole. Some extended-release capsules may be able to be opened and the contents sprinkled on applesauce then swallowed straight away. Ask your doctor about this if you have difficulty swallowing capsules.
  • The dosage of verapamil varies among individuals depending on age, the condition being treated, and the presence of other medical conditions. Your doctor will tailor your dosage to suit you.
  • Avoid grapefruit and grapefruit juice products.
  • People taking verapamil to lower high blood pressure should also make lifestyle changes including managing high blood pressure and high cholesterol, losing weight if they are overweight, stopping smoking if they smoke, and partaking in exercise as per a doctor's recommendations.
  • If verapamil makes you dizzy this may affect your ability to drive or operate machinery. Avoid doing these activities if verapamil has this effect on you.
  • Verapamil may make you feel dizzy when going from a lying or sitting position to standing, increasing your risk of falls. Stand slowly and remove any fall hazards from your home such as loose rugs.
  • Avoid or limit alcohol intake while taking verapamil because it may further lower your blood pressure or increase the likelihood of dizziness.
  • Call your doctor if you experience shortness of breath, a change in your heartbeat, light-headedness, anxiety-like feelings, loss of appetite, yellowing of the skin or eyes, or flu symptoms while taking verapamil.
  • Although verapamil works on calcium ions, it does not alter calcium levels in your blood; although high levels of blood calcium could affect the way verapamil works.
  • Your doctor will need to monitor your blood pressure, liver and kidney function regularly while you are taking verapamil.
  • Do not take any other medication, including that brought over-the-counter, without first checking with your doctor or pharmacist that it is compatible with verapamil.
  • Verapamil is best not taken during pregnancy or while breastfeeding. If you inadvertently become pregnant, tell your doctor right away.

6. Response and effectiveness

  • Peak levels of verapamil are reached one to two hours after oral administration. Peak levels may be increased in people with liver disease or of an older age.

7. Interactions

Medicines that interact with verapamil may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with verapamil. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with verapamil include:

  • alpha-blockers, such as prazosin
  • anticonvulsants, such as carbamazepine, phenytoin, or phenobarbital
  • antidepressants, such as nefazodone
  • antifungal agents, such as itraconazole and ketoconazole
  • antihypertensives, such as vasodilators, ACE inhibitors, or diuretics)
  • aspirin (may increase bleeding time)
  • barbiturates
  • beta-blockers, such as atenolol, labetalol, or metoprolol
  • budesonide
  • buspirone
  • cannabis
  • cholesterol-lowering agents (specifically HMG-CoA reductase inhibitors) such as atorvastatin, lovastatin, pravastatin, or simvastatin (may increase the risk of myopathy/rhabdomyolysis). Limit the dose of simvastatin to 10mg/day and lovastatin to 40 mg/day. Lower starting and maintenance dosages of other statins may be needed
  • cimetidine
  • codeine
  • colchicine
  • cyclosporine
  • dabigatran
  • dantrolene
  • digoxin (dosage adjustment needed)
  • disopyramide
  • domperidone
  • duloxetine
  • fentanyl
  • flecainide
  • grapefruit juice
  • ivabradine (avoid)
  • metformin
  • red yeast rice
  • rifampin
  • quinidine
  • NSAIDs, such as diclofenac, ibuprofen, and indomethacin, may decrease the blood pressure-lowering capabilities of verapamil
  • sildenafil
  • St. John's Wort
  • triazolam
  • zopiclone
  • other medications that inhibit or induce CYP 3A4, such as clarithromycin, erythromycin, or glucocorticoids.

Verapamil may also increase the effects and side effects of alcohol.

Note that this list is not all-inclusive and includes only common medications that may interact with verapamil. You should refer to the prescribing information for verapamil for a complete list of interactions.

References

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use verapamil only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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