Dextromethorphan & quinidine

treats pseudobulbar affect (PBA) which is involuntary and uncontrolled episodes of laughing/crying. Ask a doctor before using any cough/ cold medication as this medication contains a cough medicine

Dextromethorphan & quinidine Overview

Reviewed: July 7, 2015

Dextromethorphan/quinidine is a prescription medication approved for the treatment of pseudobulbar affect (PBA), a condition characterized by involuntary, sudden, uncontrolled episodes of laughing or crying, when there appears to be nothing to laugh or cry about.

This medication contains a combination of two medications: dextromethorphan hydrobromide and quinidine sulfate. Dextromethorphan is in a class of medications called central nervous system agent (nerve tissues that control activities of the body) and the way it works in the brain to treat PBA is not known. Quinidine is in a class of medications called antiarrhythmics (abnormal heart rhythm). When combined with dextromethorphan, quinidine works by increasing the amount of dextromethorphan in the body. It comes in the form of a capsule and is typically taken once or twice a day.

Common side effects of dextromethorphan/quinidine may include diarrhea and vomiting. This medication can also cause dizziness. Do not drive or operate heavy machinery until you know how it affects you.

Dextromethorphan & quinidine Genetic Information

CYP2D6 is a protein in your body that is involved in the elimination of dextromethorphan/quinidine and other drugs from your body. Some patients have less of this protein in their bodies, affecting how much of the drug gets eliminated. Levels of CYP2D6 can vary greatly between individuals, and those having less of this protein are known as "poor metabolizers." 

CYP2D6 testing is done to determine whether you are a poor metabolizer. If you are a poor metabolizer, the levels of dextromethorphan/quinidine in your blood can become too high. As a result you may be at an increased risk of having more side effects from dextromethorphan/quinidine. 

Your doctor should use caution in treating you with dextromethorphan/quinidine or your doctor may adjust your dose if you are a poor metabolizer.

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Dextromethorphan & quinidine Cautionary Labels


Uses of Dextromethorphan & quinidine

Dextromethorphan/quinidine is a prescription medication is used to treat pseudobulbar affect (PBA) a condition of sudden, frequent outbursts of crying and laughing that can not be controlled. Used in people with the following certain conditions:

  1. Amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease) - a condition in which the nerves that control muscle movement slowly die, causing muscles to shrink and weaken.
  2. Multiple Sclerosis - a disease in which the  nerves do not function properly and weakness, numbness, loss of muscle coordination and problems with vision, speech and bladder control.

This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information.

Dextromethorphan & quinidine Brand Names

Dextromethorphan & quinidine may be found in some form under the following brand names:

Dextromethorphan & quinidine Drug Class

Dextromethorphan & quinidine is part of the drug class:

Side Effects of Dextromethorphan & quinidine

Serious side effects have been reported with dextromethorphan/quinidine. See the “Drug Precautions” section.

Common side effects of dextromethorphan/quinidine include the following:

  • Diarrhea
  • Vomiting
  • Dizziness/ fainting
  • Stomach pain
  • Trouble breathing
  • Fever
  • Cough
  • Irregular/ fast heartbeat
  • Weakness
  • Muscle spasms
  • Swelling of hands, feet, ankles, or lower leg
  • Easily bruising/ bleeding
  • Lupus-like symptoms (muscle/ joint pain)
  • Frequent, painful or difficult urination
  • Dark urine

This is not a complete list of side effects. Ask your doctor or pharmacist for more information.

Tell your doctor if you have any side effect that bothers you or that does not go away.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Dextromethorphan & quinidine Interactions

Tell your doctor about all the medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements. Especially tell your doctor if you take:

  • Monoamine oxidase inhibitors (MAOIs) such as isocarboxazid (Marplan), phenelzine (Nardil), tranylcypromine (Parnate), selegiline (Emsam, Eldepryl, Zelapar) and rasagiline (Azilect). MAO inhibitors should not be taken in combination or two weeks before or after taking dextromethorphan/quinidine. 
  • Selective Serotonin reuptake inhibitors (SSRIs), Tricyclic Antidepressants and other medications that could lead to serotonin syndrome such as citalopram (Celexa), escitalopram (Lexapro), fluoxetine (Prozac, Sarafem), fluvoxamine (Luvox), desvenlafaxine (Pristiq), nefazodone (Serzone), paroxetine (Paxil, Pexeva), sertraline (Zoloft), venlafaxine (Effexor), trimipramine (Surmontil), isocarboxazid (Marplan), amitriptyline (Elavil), nortriptyline (Pamelor, Aventyl), protriptyline (Vivactil), and clomipramine (Anafranil), and linezolid (Zyvox)
  • Medications that use the enzyme CYP2D6 such as desipramine, dextromethorphan, atomoxetine
  • Medications that block a protein in the body (CYP2D6) such as quinidine (Qualaquin), fluoxetine (Prozac,Sarafem), amitriptyline (Elavil, Amitril, Amitid), and paroxetine (Paxil)
  • Medications that block a protein in the body (CYP3A4) such as some macrolide antibiotics (clarithromycin, telithromycin), some HIV protease inhibitors (indinavir, nelfinavir, ritonavir, saquinavir), some HCV protease inhibitors (boceprevir, telaprevir), some azole antifungals (ketoconazole, itraconazole, posaconazole, voriconazole), conivaptan (Vaprisol), delavirdine (Rescriptor), and nefazodone
  • Drugs that can cause an arrhythmia called Torsades des Point such as:
    • certain anti-arrhythmia medications including procainamide, sotalol (Betapace), quinidine, dofetilide (Tikosyn), amiodarone (Nexterone, Pacerone, Cordarone), ibutilide (Corvert)
    • certain fluoroquinolone antibiotics including levofloxacin (Levaquin), ciprofloxacin (Cipro), gatifloxacin (Zymar), moxifloxacin (Avelox)
    • certain macrolide antibiotics including clarithromycin (Biaxin), erythromycin (EES, others)
    • certain azole antifungals including ketoconazole (Nizoral), itraconazole (Sporanox, Onmel)
    • certain antidepressants including amitriptyline, desipramine (Norpramin), imipramine (Tofranil), doxepin (Silenor), fluoxetine (Prozac, Sarafem, Symbyax), sertraline (Zoloft), venlafaxine (Effexor XR)
    • certain antipsychotics including haloperidol (Haldol), droperidol (Inapsine), quetiapine (Seroquel XR), thioridazine, ziprasidone (Geodon), pimozide (Orap)
    • other medications including cisapride, sumatriptan (Treximet, Imitrex, Alsuma, Zecuity), zolmitriptan (Zomig), arsenic trioxide (Trisenox), dolasetron (Anzemet), and methadone (Methadone, Dolophine)

This is not a complete list of drug interactions. Ask your doctor or pharmacist for more information.

Ask your healthcare provider if you are not sure if you are taking any of these medications. 

Your healthcare provider or pharmacist can tell you if it is safe to take dextromethorphan/quinidine with your other medicines. You should carry a list and update your medication changes each time you visit the doctor, pharmacy or if are admitted to the hospital. 

Dextromethorphan & quinidine Precautions

Serious side effects have been reported with dextromethorphan/quinidine. 

1. Thrombocytopenia: Low platelets (blood cells that help blood stop bleeding) in the blood can be severe or fatal. This medication should be discontinued immediately. Watch for these changes and call your healthcare provider right away if you notice:

  • unusual bleeding
  • bruising
  • prolonged bleeding after an injury
  • lightheadedness
  • nausea and vomiting
  • chills and fever

2. Hypersensitivity: (severe allergic reaction) resulting in lupus-like syndrome (a condition in which the body attacks its own tissues causing damage and swelling) is common. Signs or symptoms of hypersensitivity, include the following:

  • swelling of the face, eyes, lips, tongue, arms, or leg
  • difficulty breathing or swallowing
  • rash

3. QT prolongation: This is a condition when changes in the electrical activity of your heart occur, causing irregular heartbeats that can be life threatening. The risk of QT prolongation may be increased if you have certain medical conditions (heart failure, slow heartbeat, blockage in ventricles of the heart, heart conditions like torsades de pointes) or are taking other drugs that may cause QT prolongation. An electrocardiogram ECG (measure electrical activity in the heart) will need to be done before and during treatment. Tell your healthcare provider right away if you are taking other drugs that may cause QT prolongation or have any signs or symptoms including:

  • fainting
  • irregular heartbeat
  • lightheadedness
  • dizziness

4. Low Potassium and Magnesium Blood levels: 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.

4. Hepatitis: Inflammation of the liver usually occurs during the first few weeks of therapy. Tell your healthcare provider about any signs or symptoms of liver damage, which include the following fever or thrombocytopenia (low blood cells that help blood clot) or hypersensitivity signs.

5. Myasthenia Gravis: A disorder of the nervous system that causes muscle weakness throughout the body. The first symptoms you may notice are eyelid drooping and/or blurred or double vision.

6. Bone marrow depression: Low blood cell counts. This medication can affect your bone marrow and cause you to have low blood cell counts. Your doctor will need to order labs to monitor for this. Report symptoms of

  • shortness of breath
  • ongoing cough and congestion
  • significant fatigue 
  • fever 
  • chills
  • sore throat
  • other signs of infection

7. Serotonin Syndrome: Serotonin is a chemical that your body produces for nerve cells and brain to function. Some medications can cause high levels of serotonin to build up in your body.  Serotonin syndrome can be fatal if not treated. Symptoms may range from:

  • mild (shivering, goosebumps, headache, heavy sweating, agitation and diarrhea)
  • severe (muscle stiffness, irregular heartbeat, high blood pressure, high fever, seizures, unconsciousness)

Dextromethorphan/quinidine can cause drowsiness. Precautions to reduce the risk of falls should be taken. Do not drive or operate heavy machinery until you know how this medication affects you.

Do not take dextromethorphan/quinidine if you:

  • are allergic to dextromethorphan/quinidine or any of its ingredients
  • are taking quinidine, quinine, or mefloquine.
  • have a history of quinidine, quinine or mefloquine-induced thrombocytopenia, hepatitis, or other hypersensitivity reactions.
  • have a known hypersensitivity to dextromethorphan
  • have are taking or have taken an MAOI within 14 days. Allow 14 days after stopping this medication before starting an MAOI.
  • have prolonged QT interval, congenital long QT syndrome, history suggestive of torsades de pointes, or heart failure
  • have complete atrioventricular (AV) block without implanted pacemaker, or patients at high risk of complete AV block.
  • are taking drugs that both prolong QT interval and are metabolized by CYP2D6 (e.g., thioridazine or pimozide)

Dextromethorphan & quinidine Food Interactions

Grapefruit and grapefruit juice may interact with dextromethorphan/quinidine and lead to potentially dangerous effects. Discuss the use of grapefruit products with your doctor

Alcohol can make the side effects from this medication worse. Ask your doctor about sate use if alcoholic beverages while you are taking dextromethorphan/quinidine.

Inform MD

Before taking dextromethorphan/quinidine, tell your doctor about all of your medical conditions. Especially tell your doctor if you:

  • are allergic to dextromethorphan and quinidine
  • are taking any other medications that contain dextromethorphan, quinidine, quinine or mefloquine as an ingredients. Ask your pharmacist for a list of the ingredients in other medications you are taking.
  • have or have had bone marrow depression (decrease in number of blood cells in bone marrow)
  • have liver problems (hepatitis- swelling of the liver)
  • have heart problems -  Heart failure and QT prolongation (condition affecting the heart rhythm) may result in fast/irregular heartbeat and fatal complications. Are taking any medications that can cause QT prolongation. An electrocardiogram ECG (measure electrical activity in the heart) will need to be done before and during treatment. 
  • are pregnant or breastfeeding
  • have or have had lupus like syndrome (a condition in which the body attacks its own tissues causing damage and swelling)
  • have kidney problems
  • have ever had myasthenia gravis (a disorder of the nervous system that causes muscle weakness)
  • have low levels of potassium or magnesium in your blood (need to be monitored before and while taking this medication)
  • have high blood pressure
  • have had a stroke  
  • have or are taking monoamine oxidase inhibitors (MAOIs) within the last 14 days, due to the risk of serious and possibly fatal drug interactions.

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements.

Dextromethorphan & quinidine and Pregnancy

Tell your doctor if you are pregnant or plan to become pregnant.

The FDA categorizes medications based on safety for use during pregnancy. Five categories - A, B, C, D, and X, are used to classify the possible risks to an unborn baby when a medication is taken during pregnancy.

Dextromethorphan/quinidine falls into Category C. In animal studies, pregnant animals were given this medication and had some babies born with problems. No well-controlled studies have been done in humans. Therefore, this medication may be used if the potential benefits to the mother outweigh the potential risks to the unborn child.

Dextromethorphan & quinidine and Lactation

Tell your doctor if you are breastfeeding or plan to breastfeed.

It is not known if dextromethorphan/quinidine crosses into human milk. Because many medications can cross into human milk and because of the possibility for serious adverse reactions in nursing infants with use of this medication, a choice should be made whether to stop nursing or stop the use of this medication. Your doctor and you will decide if the benefits outweigh the risk of using this medication.

Dextromethorphan & quinidine Usage

Take dextromethorphan/quinidine exactly as prescribed.

This medication comes in a single capsule combination medication of dextromethorphan hydrobromide 20 mg and quinidine sulfate 10mg. 

Take dextromethorphan/quinidine by mouth at the same time every day.

Do not break or chew the capsules. Swallow it whole. Take with a full glass of water 8 ounces (240 milliliters). It may be taken with or without food. Avoid eating grapefruit or drinking grapefruit juice while being treated with this medication.

If you miss a dose, skip the missed dose and take the next dose at the regular time. Do not take two doses of this medication to make up for missed one. Be sure to allow 12 hours between doses. Do not take more than 2 doses in a 24 hour period.


Dextromethorphan & quinidine Dosage

Take this medication exactly as prescribed by your doctor. Follow the directions on your prescription label carefully. The need for continued treatment should be reassessed periodically, as spontaneous improvement of PBA occurs in some patients.

The recommended dose/dose range of Nuedexta (dextromethorphan/quinidine) for the treatment of pseudobulbar affect (PBA) which is involuntary and uncontrolled episodes of laughing/crying is

The recommended starting dose is 1 capsule daily by mouth for the initial 7 days of therapy.

The recommended maintenance dose is 1 capsule by mouth every 12 hours.

Do not take more than 2 doses in a 24 hour period and be sure to allow 12 hours between each dose.

Dextromethorphan & quinidine Overdose

If you take too much of this medication, call your healthcare provider or local Poison Control Center, or seek emergency medical attention right away. 

The most important effects if acute quinidine overdose:

  • changes in heartbeat
  • low blood pressure
  • vomiting
  • diarrhea
  • ringing in the ears
  • dizziness/ fainting
  • blurred or double vision
  • headache
  • confusion
  • delirium
The most important effects of dextromethorphan overdose:
  • nausea
  • vomiting
  • loss of consciousness
  • difficulty breathing
  • seizures
  • unusual excitement
  • abornmal thinking
  • changes in muscle reflexes
  • changes in heartbeat


Other Requirements


  • Store at room temperature and away from excess heat, light and moisture (not in bathroom). 
  • Keep this and all medicines tightly closed out of the reach of children.
  • Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about proper disposal of your medication.


  • Contact you healthcare provider if PBA symptoms persist or worsen. The need for continued treatment should be reassessed      periodically, as spontaneous improvment of PBA occurs in some patients.
  •  An ECG an electrocardiogram ECG (measure electrical acitivity in the heart) will need to be done before and while taking this medication.
  • Lab tests including liver function, complete blood count and levels of potassium or magnesium in your blood need to be monitored before and while taking this medication.