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Patients taking the commonly prescribed calcium channel blocker felodipine (available in generics only) should be aware that it has clinically important interactions with many other prescription medications as well as the dietary supplement St. John’s wort.
Felodipine initially was approved by the Food and Drug Administration in 1991 and is approved only for the treatment of hypertension (high blood pressure).[1] It often is used in combination with other antihypertensive medications.
Drug...
Patients taking the commonly prescribed calcium channel blocker felodipine (available in generics only) should be aware that it has clinically important interactions with many other prescription medications as well as the dietary supplement St. John’s wort.
Felodipine initially was approved by the Food and Drug Administration in 1991 and is approved only for the treatment of hypertension (high blood pressure).[1] It often is used in combination with other antihypertensive medications.
Drugs that may increase risk of felodipine toxicity[2],[3]
Like many drugs, felodipine is metabolized (broken down or chemically modified) by substances in the liver called enzymes. One important liver enzyme, known as CYP3A4, breaks down felodipine and helps eliminate it from the body.
The Table below provides examples of oral drugs that can inhibit CYP3A4. The list includes certain antibiotics, antifungal drugs and antiviral drugs for HIV infection, as well as the immunosuppressant/organ-transplant drug cyclosporine (GENGRAF, NEORAL, SANDIMMUNE) and the stomach-acid–suppressing histamine-2 receptor blocker cimetidine (TAGAMET HB).
When taken concomitantly (at the same time) with felodipine, these CYP3A4-inhibiting drugs, because they decrease the rate of felodipine breakdown, can thereby increase felodipine levels in the blood to toxic levels. Felodipine toxicity may result in dangerously low blood pressure and rapid or slow heart rate.
Examples of Oral Drugs That Can Increase Risk of Felodipine Toxicity
| Generic Name | Brand Name(s)† | Drug Class |
|---|---|---|
| atazanavir | REYATAZ | Antiviral drug for HIV infection |
| cimetidine | TAGAMET HB | Histamine-2 receptor blocker |
| clarithromycin* | BIAXIN XL | Macrolide antibiotic |
| cyclosporine | GENGRAF, NEORAL, SANDIMMUNE | Immunosuppressant/organ-transplant drug |
| erythromycin | E.E.S., E.E.S. 400, ERY-TAB, ERYC, ERYPED | Macrolide antibiotic |
| fluconazole | DIFLUCAN | Antifungal drug |
| itraconazole** | SPORANOX, TOLSURA | Antifungal drug |
| ketoconazole*** | generic only | Antifungal drug |
| nelfinavir | VIRACEPT | Antiviral drug for HIV infection |
†Brand-name combination products containing other active ingredients were excluded.
*Designated as Limited Use by Worst Pills, Best Pills News
**Designated as Do Not Use except for serious fungal infection by Worst Pills, Best Pills News
***Designated Do Not Use by Worst Pills, Best Pills News
Drugs that may decrease felodipine’s effectiveness[4],[5],[6]
Certain oral seizure medications — including carbamazepine (CARBATROL, EPITOL, EQUETRO, TEGRETOL, TERIL) and oxcarbazepine (OXTELLAR XR, TRILEPTAL) — can increase the activity of the CYP3A4 liver enzyme.
When taken concomitantly with felodipine, these CYP3A4-stimulating drugs — because they increase the rate of felodipine breakdown — can thereby decrease felodipine levels in the blood, possibly resulting in inadequate treatment of hypertension.
The dietary supplement St. John’s wort also can increase the activity of the CYP3A4 liver enzyme. Concomitant use of this supplement with felodipine thus can potentially lead to decreased felodipine blood levels and inadequate treatment of hypertension.
Other important interactions[7],[8]
Clopidogrel (PLAVIX)
Concomitant use of felodipine with the antiplatelet drug clopidogrel, which is used to reduce the risks of heart attack and stroke in certain patients at high risk of such events, may block the activation of clopidogrel and thus interfere with its antiplatelet effects and ability to prevent a heart attack or stroke.
Digoxin (LANOXIN)
Concomitant use of felodipine with the heart drug digoxin, which is used to treat heart failure and control the heart rate in atrial fibrillation, may result in a heart problem known as complete heart block and a slow heart rate, as well as transient increased levels of digoxin, which could lead to digoxin toxicity in certain patients. Symptoms of digoxin toxicity include loss of appetite, nausea, vomiting and fatigue. Patients taking digoxin may need a dosage change and should undergo more frequent monitoring of blood digoxin levels after starting, stopping or adjusting the dosage of felodipine.
Grapefruit juice
Grapefruit contains a substance that inhibits the CYP3A4 liver enzyme. Consuming grapefruit juice while taking felodipine has been shown to cause an up to a threefold increase in felodipine blood levels, potentially leading to felodipine toxicity. Patients taking felodipine should avoid ingesting grapefruit and grapefruit juice. Additionally, grapefruit juice should be discontinued for two to three days before felodipine therapy is initiated.
What You Can Do
If you need treatment with felodipine, review all your other medications with your doctor to assess for potentially significant drug interactions. If you are taking certain medications that interact with felodipine, you may need to adjust the dosage of the interacting drug or undergo more frequent monitoring of the blood levels of the interacting drug, or your doctor may advise you to take a different drug for your hypertension. Do not consume grapefruit juice while taking felodipine. Be aware that other drugs not listed in this article also may have dangerous interactions with felodipine.
Finally, talk to your doctor before changing or discontinuing any prescription medication.
References
[1] Torrent Pharmaceuticals. Label: felodipine. July 2022. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=60fb803e-ccf7-46f2-b506-e157ce440f87&type=display. Accessed February 8, 2023.
[2] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “felodipine.” Accessed February 8, 2023.
[3] Torrent Pharmaceuticals. Label: felodipine. July 2022. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=60fb803e-ccf7-46f2-b506-e157ce440f87&type=display. Accessed February 8, 2023.
[4] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “felodipine.” Accessed February 8, 2023.
[5] Torrent Pharmaceuticals. Label: felodipine. July 2022. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=60fb803e-ccf7-46f2-b506-e157ce440f87&type=display. Accessed February 8, 2023.
[6] Andreasen AH, Brøsen K, Damkier P. A comparative pharmacokinetic study in healthy volunteers of the effect of carbamazepine and oxcarbazepine on cyp3a4. Epilepsia. 2007;48(3):490-496.
[7] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “felodipine.” Accessed February 8, 2023.
[8] Torrent Pharmaceuticals. Label: felodipine. July 2022. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=60fb803e-ccf7-46f2-b506-e157ce440f87&type=display. Accessed February 8, 2023.
