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This medication is used to treat or prevent many types of irregular heartbeats (heart arrhythmias such as atrial fibrillation). Quinidine can greatly improve your ability to perform normal activities by decreasing the number of irregular heartbeats you have. However, it may not stop all your irregular heartbeats completely. It works by blocking abnormal heartbeat signals.
Before and while you are using quinidine, your doctor may prescribe other medications (e.g., "blood thinners"/anticoagulants such as warfarin, beta blockers such as metoprolol) to shrink any blood clots in the heart and to slow your pulse.
Before starting this drug, the manufacturer recommends that you take a test dose (usually a smaller amount than your regular dose) to determine whether you are allergic to it. Consult your doctor or pharmacist for details.
Take this medication by mouth with or without food with a full glass of liquid (8 ounces/240 milliliters) as directed by your doctor. This medication is best taken on an empty stomach, but taking it with food may help decrease stomach upset. Do not lie down for 10 minutes after taking this medication.
Do not crush or chew extended-release tablets. Doing so can release all of the drug at once, increasing the risk of side effects. Also, do not split the tablets unless they have a score line and your doctor or pharmacist tells you to do so. Swallow the whole or split tablet without crushing or chewing.
There are different brands and forms of this medication available. Not all have identical effects. Do not change quinidine products without talking to your doctor or pharmacist.
Dosage is based on your medical condition and response to treatment. If you are taking regular-release quinidine for an irregular heartbeat, the manufacturer recommends that you take no more than 4 grams daily.
Avoid eating grapefruit or drinking grapefruit juice while being treated with this medication unless your doctor instructs you otherwise. Grapefruit juice can change the amount of certain medications in your bloodstream. Consult your doctor or pharmacist for more details.
Avoid large changes in your dietary salt intake while being treated with this medication unless your doctor instructs you otherwise. The amount of salt in your diet may affect the amount of quinidine absorbed by your system. Consult your doctor or pharmacist for more details.
Use this medication regularly to get the most benefit from it. To help you remember, take it at the same time(s) each day.
Tell your doctor if your condition does not improve or if it worsens.
Diarrhea, nausea, vomiting, loss of appetite, stomach pain/cramps, or a burning feeling in throat or chest (e.g., heartburn) may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.
Tell your doctor right away if you have any serious side effects, including: vision changes, eye pain, muscle pain, unusual sweating or shakiness (signs of low blood sugar), unexplained fever/signs of infection (e.g., persistent sore throat), easy bruising/bleeding, extreme tiredness, dark urine, persistent nausea/vomiting, yellowing eyes/skin, lupus-like symptoms (joint/muscle pain, chest pain).
Get medical help right away if you have any very serious side effects, including: severe dizziness, fainting, sudden change in heartbeat (faster/slower/more irregular).
One type of reaction (cinchonism) can occur after even a single dose of this drug. Contact your doctor of pharmacist promptly if you notice symptoms such as ringing in the ears, sudden hearing problems, headache, blurred vision, confusion. Your dosage may need to be adjusted.
Certain long-acting brands of quinidine may appear as a whole tablet in the stool. This is the empty shell left after the medicine has been absorbed by the body. It is harmless.
Before taking quinidine, tell your doctor or pharmacist if you are allergic to it; or to quinine; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.
Before using this medication, tell your doctor or pharmacist your medical history, especially of: certain types of heart disease (e.g., incomplete or complete heart block without an artificial pacemaker, torsades-type irregular heartbeats, digitalis toxicity), very low blood pressure, history of easy bruising/bleeding (thrombocytopenic purpura) with use of quinine or quinidine, severe muscle weakness (myasthenia gravis), kidney disease, liver disease, a certain blood disorder (G6PD deficiency), asthma, current infection with fever.
Quinidine may cause a condition that affects the heart rhythm (QT prolongation). QT prolongation can rarely cause serious (rarely fatal) fast/irregular heartbeat and other symptoms (such as severe dizziness, fainting) that require immediate medical attention right away.
The risk of QT prolongation may be increased if you have certain medical conditions or are taking other drugs that may cause QT prolongation. Before using quinidine, tell your doctor or pharmacist of all the drugs you take and if you have any of the following conditions: certain heart problems (heart failure, slow heartbeat, QT prolongation in the EKG), family history of certain heart problems (QT prolongation in the EKG, sudden cardiac death).
Low levels of potassium or magnesium in the blood may also increase your risk of QT prolongation. This risk may increase if you use certain drugs (such as diuretics/"water pills") or if you have conditions such as severe sweating, diarrhea, or vomiting. Talk to your doctor about using quinidine safely.
This drug may make you dizzy. Do not drive, use machinery, or do any activity that requires alertness until you are sure you can perform such activities safely. Limit alcoholic beverages.
Before having surgery, tell your doctor that you are using this medication.
Older adults may be more sensitive to the side effects of this drug, especially dizziness and QT prolongation (see above).
During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.
This medication passes into breast milk. Consult your doctor before breast-feeding.
Store at room temperature away from light and moisture. Do not store in the bathroom. Keep all medications away from children and pets.
See also the How to Use section.
Some products that may interact with this drug include: large amounts of antacids (e.g., sodium bicarbonate), arbutamine, aripiprazole, atomoxetine, carbonic anhydrase inhibitors (e.g., acetazolamide), cisapride, etravirine, fingolimod, fosamprenavir, loperamide, certain macrolide antibiotics (e.g., erythromycin, clarithromycin), phenytoin, propafenone, quinupristin/dalfopristin, rifamycins (e.g., rifampin, rifabutin).
Other medications can affect the removal of quinidine from your body, which may affect how quinidine works. Examples include cobicistat, mifepristone, certain azole antifungals (including fluconazole, itraconazole, ketoconazole, posaconazole, voriconazole), certain protease inhibitors (such as nelfinavir, ritonavir, tipranavir), among others.
This medication can slow down the removal of other medications from your body, which may affect how they work. Examples of affected drugs include aliskiren, codeine, digoxin, mefloquine, tricyclic antidepressants (such as desipramine, imipramine), among others.
Many drugs besides quinidine may affect the heart rhythm (QT prolongation), including artemether/lumefantrine, ranolazine, toremifene, antiarrhythmic drugs (such as amiodarone, disopyramide, dofetilide, dronedarone, ibutilide, procainamide, sotalol), antipsychotics (such as pimozide, thioridazine, ziprasidone), certain quinolone antibiotics (grepafloxacin, sparfloxacin), among others.
Quinidine is very similar to quinine. Do not use medications containing quinine while using quinidine.
If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: severe dizziness/fainting, hallucinations, seizures.
If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.
Do not share this medication with others.
Laboratory and/or medical tests (e.g., complete blood count, liver/kidney function tests, quinidine blood levels, EKG) should be performed periodically to monitor your progress or check for side effects. Consult your doctor for more details.