Quinidine

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

May be Beneficial: Side effect reduction/prevention—Taking these supplements may help reduce the likelihood and/or severity of a potential side effect caused by the medication.	Beta-carotene Magnesium Potassium
May be Beneficial: Supportive interaction—Taking these supplements may support or otherwise help your medication work better.	Food
Avoid: Reduced drug absorption/bioavailability—Avoid these supplements when taking this medication since the supplement may decrease the absorption and/or activity of the medication in the body.	High-salt diet
Avoid: Adverse interaction—Avoid these supplements when taking this medication because taking them together may cause undesirable or dangerous results.	Food Grapefruit juice Low-salt diet Sodium bicarbonate
Depletion or interference	None known

Interactions with Dietary Supplements

Potassium and Magnesium
People taking potassium-depleting diuretics may develop low potassium and magnesium blood levels. Prolonged diarrhea and vomiting might also result in low blood potassium levels. People with low potassium or magnesium blood levels who take quinidine might develop serious drug side effects.¹ Therefore, people taking quinidine should have their blood potassium and magnesium levels checked regularly and might need to supplement with both minerals, especially when taking potassium-depleting diuretics.

Beta-carotene
Some people taking quinidine develop sensitivity to ultraviolet radiation from the sun. In a preliminary study, three people with quinidine-induced skin inflammation were able to tolerate intense sun exposure without recurrence of the rash after supplementing with 90–180 mg of beta-carotene each day.² Further research is needed to confirm that people taking quinidine can prevent side effects by supplementing with beta-carotene.

Interaction with Foods and Other Compounds

Grapefruit juice
Drinking grapefruit juice together with quinidine increases the amount of time that the drug remains in the body,³ which might increase the likelihood of side effects and toxicity. Therefore, based on currently available information, people taking quinidine should avoid drinking grapefruit juice or eating grapefruit.

Salt
One controlled study showed that people consuming a high-salt diet had dramatically lower quinidine blood levels compared with people on a low-salt diet.⁴ Problems might occur when people switch from a high-salt diet to a low-salt diet and vice versa. Therefore, people taking quinidine should notify their health practitioner before changing their salt intake.

Food
Taking quinidine with food greatly increases the speed and extent of absorption of the drug.⁵ Serious problems might occur when people switch from taking quinidine with a meal to taking it on an empty stomach and vice versa. Therefore, quinidine should be consistently taken with a meal to enhance drug action and to avoid potential problems.

Sodium bicarbonate
Sodium bicarbonate reduces the amount of quinidine eliminated from the body, which might result in increased drug side effects and toxicity.⁶ Therefore, people taking quinidine should avoid using antacids or toothpaste that contain sodium bicarbonate.

References

1. Roden DM, Iansmith DH. Effects of low potassium or magnesium concentrations on isolated cardiac tissue. Am J Med 1987;82:18–23.

2. Fisher DA. Quinidine photosensitivity. Arch Dermatol 1984;120:298 [letter].

3. Damkier P, Hansen LL, Brosen K. Effect of diclofenac, disulfiram, itraconazole, grapefruit juice and erythromycin on the pharmacokinetics of quinidine. Br J Clin Pharmacol 1999;48:829–38.

4. Darbar D, Dell’Orto S, Morike K, et al. Dietary salt increases first-pass elimination of oral quinidine. Clin Pharmacol Ther 1997;61:292–300.

5. Sifton DW, et. Physicians’ Desk Reference. Montvale, NJ: Medical Economics Company, Inc., 2000, 757–60.

6. Sifton DW, et. Physicians’ Desk Reference. Montvale, NJ: Medical Economics Company, Inc., 2000, 757–60.

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The information presented in Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over-the-counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires July 2004.