Felodipine

Also indexed as: Plendil®

Felodipine is used to treat high blood pressure, Raynaud’s syndrome, and congestive heart failure. It is in a class of drugs known as calcium channel blockers.

Summary of Interactions with Vitamins, Herbs, and Foods
(for details about the summarized interactions, read the full article)

Beneficial May be Beneficial: Depletion or interference—The medication may deplete or interfere with the absorption or function of the nutrient. Taking these nutrients may help replenish them.

Calcium

Magnesium

Potassium
Avoid Avoid: Adverse interaction—Avoid these supplements when taking this medication because taking them together may cause undesirable or dangerous results.

Grapefruit juice

Pleurisy root*

Quercetin*
Side effect reduction/prevention

None known
Supportive interaction

None known
Reduced drug absorption/bioavailability

None known

An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.

Interactions with Dietary Supplements

Potassium
Felodipine can lead to increased excretion of potassium.1 A potassium deficiency may result if potassium intake is not sufficient. People taking felodipine should eat a high-potassium diet and be checked regularly for low blood potassium by a doctor.

Magnesium
Increased magnesium excretion has been observed in studies of individuals taking felodipine.2 Therefore, some physicians may recommend magnesium supplementation to their patients taking felodipine.

Calcium
A study of felodipine indicated that the drug caused increased excretion of calcium.3 Whether this effect could lead to increased bone loss is unknown, but some health practitioners may recommend calcium supplementation to individuals taking felodipine. Although the effectiveness of some calcium channel blockers may be reduced with calcium supplementation,4 this effect has not been observed in people taking felodipine.

Quercetin
Quercetin is a flavonoid found in grapefruit juice, tea, onions, and other foods; it is also available as a nutritional supplement. Quercetin has been shown in test tube studies to inhibit enzymes responsible for breaking down felodipine into an inactive form.5 This interaction may result in increased blood levels of felodipine that could lead to unwanted side effects. Until more is known about this interaction, patients taking felodipine should avoid supplementing with quercetin.

Interactions with Herbs

Pleurisy root
As pleurisy root and other plants in the Aesclepius genus contain cardiac glycosides, it is best to avoid use of pleurisy root with heart medications such as calcium channel blockers.6

Interactions with Foods and Other Compounds

Grapefruit
Regular consumption of grapefruit juice can increase the quantity of felodipine in the blood by reducing the breakdown of the drug.7 The inhibitory effect of grapefruit juice lasts up to 24 hours after ingestion and can increase blood levels nearly three times the expected amount. In order to prevent side effects of the drug, individuals who are taking felodipine should avoid grapefruit and its juice.

Alcohol
Drinking alcoholic beverages while taking felodipine may enhance the blood pressure–lowering effect of the drug.8 Those who combine alcoholic beverages with felodipine should be aware of possible adverse consequences, such as increased lightheadedness.

References

1. Hulthen UL, Katzman PL. Renal effects of acute and long-term treatment with felodipine in essential hypertension. J Hypertens 1988;6:231–7.

2. Hulthen UL, Katzman PL. Renal effects of acute and long-term treatment with felodipine in essential hypertension. J Hypertens 1988;6:231–7.

3. Hulthen UL, Katzman PL. Renal effects of acute and long-term treatment with felodipine in essential hypertension. J Hypertens 1988;6:231–7.

4. Werbach MR. Foundations of Nutritional Medicine. Tarzana, CA: Third Line Press, Inc., 1997, 208.

5. Miniscalco A, Lundahl J, Regardh CG. Inhibition of dihydropyridine metabolism in rat and human liver microsomes by flavonoids found in grapefruit juice. J Pharmacol Exp Ther 1992;261:1195–9.

6. Newall CA, Anderson LA, Phillipson JD. Herbal Medicines: A Guide for Health-Care Professionals. London: Pharmaceutical Press, 1996, 213–4.

7. Bailey DG, Malcolm J, Arnold O, Spence JD. Grapefruit juice-drug interactions. Br J Clin Pharmacol 1998;46:101–10.

8. Bailey DG, Spence JD, Edgar B, et al. Ethanol enhances the hemodynamic effects of felodipine. Clin Invest Med 1989;12:357–62.