Important Drug Interactions for the Calcium Channel Blocker Verapamil

Patients taking the widely prescribed calcium channel blocker verapamil (CALAN SR, VERELAN) should be aware that it has clinically important interactions with many other prescription medications.

Verapamil was approved by the Food and Drug Administration in 1984 and is used to treat hypertension (high blood pressure), angina (chest pain that often spreads to the shoulders, arms and neck and that is caused by inadequate blood flow to the heart) and certain abnormal heart rhythms characterized by a rapid or irregular heart rate, including atrial fibrillation.[1]

The list of drugs that can interact with verapamil and result in potential harm includes antibiotics, beta blockers, cholesterol-lowering statins and other drugs for treating abnormal heart rhythms (see Table, below, for examples).[2],[3]

Examples of Oral Drugs That Have Clinically Important Interactions with Verapamil

†Brand-name combination products were excluded.
*Designated as Limited Use
**Designated as Do Not Use
***The 80-milligram dose of simvastatin is designated as Do Not Use.

Beta blockers and clonidine[4],[5]

Beta blockers (such as atenolol [TENORMIN] and metoprolol [KAPSPARGO SPRINKLE, LOPRESSOR, TOPROL-XL]) are a large family of medications widely used to treat hypertension. Certain beta blockers also are approved for treating abnormal heart rhythms, angina, heart failure, heart attacks or migraines.

Patients with hypertension, angina and other heart conditions often are appropriately prescribed both a calcium channel blocker, such as verapamil, and a beta blocker. Patients need to be aware that such concomitant (concurrent) use of verapamil with any beta blocker may cause low blood pressure and a very low heart rate, which could lead to light-headedness and fainting.

These adverse effects can occur because both verapamil and beta blockers can slow the heart rate and decrease the strength of heart muscle contractions. Patients — particularly those with heart failure — who are taking verapamil and a beta blocker need to have their heart function, blood pressure and heart rate monitored carefully.

Similarly, concomitant use of verapamil with the hypertension drug clonidine (CATAPRES, KAPVAY), which Public Citizen’s Health Research Group has designated as Do Not Use, can cause a dangerously low heart rate.

Interactions involving effects on liver enzymes[6],[7]

Verapamil can inhibit certain liver enzymes involved in the breakdown of many other drugs. As a result, concomitant use of verapamil with these drugs can increase the blood levels of the interacting drugs, potentially leading to toxicity.

For example, concomitant use of verapamil with atorvastatin (LIPITOR), lovastatin (ALTOPREV) or simvastatin (FLOLIPID, ZOCOR) can lead to toxic blood levels of these cholesterol-lowering statins. Statin toxicity can cause muscle pain and, in more severe cases, rhabdomyolysis (muscle breakdown), which can lead to sudden kidney failure.

Similarly, concomitant use of verapamil with the gout drug colchicine (COLCRYS, GLOPERBA, MITIGARE), the heart drug digoxin (LANOXIN) or the super-potent opioid fentanyl (ACTIQ, DURAGESIC, FENTORA, LAZANDA, SUBSYS) can lead to potentially life-threatening colchicine, digoxin or fentanyl toxicity, respectively.

Other important interactions[8],[9]

Concomitant use of verapamil with the bipolar disorder drug lithium (LITHOBID) may increase the risk of lithium-induced nervous system toxicity. Verapamil also can have unpredictable effects on lithium blood levels, sometimes increasing and sometimes decreasing the levels. Patients taking both drugs need careful monitoring of blood lithium levels.

Concomitant use of verapamil with the antibiotic erythromycin (E.E.S., ERY-TAB, ERYC, ERYPED, ERYTHROCIN) can cause prolongation of the QT interval. QT prolongation is a change in the electrical activity of the heart that can lead to a fatal heart rhythm disturbance called torsades de pointes, which can cause cardiac arrest and sudden death.

What You Can Do

If you need treatment with verapamil, review all of your other medications with your doctor to assess for potentially significant drug interactions. Be aware that other drugs not listed in this article also may have dangerous interactions with verapamil. In some cases, if you are taking verapamil concomitantly with another interacting drug, the dosage of one or both drugs may need to be adjusted to prevent adverse effects or inadequate treatment.
 

References

[1] Pfizer. Label: verapamil (CALAN). September 2017. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/018817s033lbl.pdf. Accessed January 13, 2020.

[2] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “verapamil.” Accessed January 13, 2020.

[3] Pfizer. Label: verapamil (CALAN). September 2017. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/018817s033lbl.pdf. Accessed January 13, 2020.

[4] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “verapamil.” Accessed January 13, 2020.

[5] Pfizer. Label: verapamil (CALAN). September 2017. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/018817s033lbl.pdf. Accessed January 13, 2020.

[6] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “verapamil.” Accessed January 13, 2020.

[7] Pfizer. Label: verapamil (CALAN). September 2017. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/018817s033lbl.pdf. Accessed January 13, 2020.

[8] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “verapamil.” Accessed January 13, 2020.

[9] Pfizer. Label: verapamil (CALAN). September 2017. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/018817s033lbl.pdf. Accessed January 13, 2020.