Important Drug Interactions for Quinidine

Patients taking the drug quinidine should be aware that it has clinically important and potentially dangerous interactions with many other prescription medications.

Quinidine, which has been marketed in the U.S. for more than six decades and is currently available in generic forms, is approved by the Food and Drug Administration (FDA) for several types of heart-rhythm disorders, including certain forms of atrial fibrillation (a common heart-rhythm disorder characterized by an irregular and often rapid heart rate) and life-threatening ventricular tachycardia.[1] The drug is also FDA-approved to treat types of life-threatening malaria. Public Citizen’s Health Research Group has designated quinidine as Limited Use.

Quinidine also is marketed as a combination product under the brand name NUEDEXTA, which also contains dextromethorphan, for treatment of pseudobulbar affect (PBA). PBA occurs in patients with a variety of otherwise unrelated neurological disorders and is characterized by involuntary, sudden and frequent episodes of laughing or crying.[2] The typical daily dose of Nuedexta provides 20 mg of quinidine, which is less than 5% of the daily dose used with quinidine-only products, making it far less likely to cause clinically important drug interactions.

Increased risk of fatal heart-rhythm abnormalities[3]

Quinidine can cause prolongation of the QT interval — 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.

Numerous oral drugs, when used concomitantly (at the same time) with quinidine, further increase the risk of QT prolongation because they either increase the blood levels of quinidine or directly cause QT prolongation (see Table, below, for examples). Such drugs include certain medications for treating heart-rhythm disorders, Alzheimer’s disease, bacterial infections, depression, fungal infections, HIV infection, muscle spasms, opioid-use disorder, pain and psychosis, among other diseases.

For several of these drugs, the risk of QT prolongation and potentially fatal abnormal heart rhythms is so high that they should not be taken concomitantly with quinidine.

Examples of Oral Drugs That May Increase the Risk of Fatal Heart-Rhythm Abnormalities When Used Concomitantly With Quinidine

†Brand-name combination products were excluded.
*Designated as Limited Use by Worst Pills, Best Pills News
**Designated as Do Not Use by Worst Pills, Best Pills News
***Designated as Do Not Use except for serious fungal infection by Worst Pills, Best Pills News

Other important drug interactions[4],[5]

Colchicine

Concomitant use of quinidine and the gout drug colchicine (COL-PROBENECID, COLCRYS, GLOPERBA, MITIGARE) may result in increased and potentially toxic blood levels of colchicine. Colchicine toxicity typically causes gastrointestinal symptoms, including abdominal pain, nausea, vomiting and diarrhea. It also can impair the bone marrow’s ability to make red and white blood cells, resulting in severe anemia and increasing the risk of serious infections, respectively.

In patients with impaired kidney or liver function, this concomitant use of quinidine and colchicine should be avoided because of the potential for life-threatening or fatal drug interactions. In patients with normal kidney and liver function who need to use quinidine and colchicine concomitantly, the colchicine dosage should be reduced.

Digoxin

Concomitant use of quinidine and digoxin (LANOXIN) — which is used to treat heart failure and to control heart rate in patients with atrial fibrillation — can result in increased and potentially highly toxic blood levels of digoxin. Common symptoms of digoxin toxicity are loss of appetite, nausea, vomiting and fatigue. Digoxin toxicity can lead to abnormal heart rhythms. If concomitant use of quinidine and digoxin is unavoidable, digoxin dosage usually should be reduced, and more frequent monitoring of blood digoxin levels should occur, especially during initiation and discontinuation of quinidine.

What You Can Do

If you need treatment with quinidine, review all your other medications with your doctor to assess for potentially significant drug interactions. If you are taking a medication that interacts with quinidine, you may need to stop or adjust the dosage of the interacting drug, undergo more frequent monitoring of the blood levels of the interacting drug, or your doctor may advise you to take a different drug than quinidine for your heart problem or malaria. Be aware that other drugs not listed in this article also may have dangerous interactions with quinidine.
 

References

[1] Epic Pharma LLC. Label: quinidine sulfate. July 2021. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=b0d6341b-d880-4f0b-8844-bc788c03004a&type=display. Accessed April 4, 2022.

[2] Avanir Pharmaceuticals, Inc.. Label: olanzapine and fluoxetine (SYMBYAX). September 2021. https://www.accessdata.fda.gov/drugsatfda_docs/label/2019/021879s014lbl.pdf. April 4, 2022.

[3] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search terms: “quinidine gluconate” and “quinidine sulfate.” Accessed March 10, 2022.

[4] Epic Pharma LLC. Label: quinidine sulfate. July 2021. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=b0d6341b-d880-4f0b-8844-bc788c03004a&type=display. Accessed April 4, 2022.

[5] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search terms: “quinidine gluconate” and “quinidine sulfate.” Accessed March 10, 2022.