Dextromethorphan and Quinidine

Dextromethorphan And Quinidine
Dextromethorphan And Quinidine


The combination of dextromethorphan and quinidine is used to treat pseudobulbar affect (PBA; a condition of sudden, frequent outbursts of crying or laughing that can not be controlled) in people with certain conditions such as amyotrophic lateral sclerosis (ALS, Lou Gehrig’s disease; a condition in which the nerves that control muscle movement slowly die, causing the muscles to shrink and weaken) or multiple sclerosis (a disease in which the nerves do not function properly and patients may experience weakness, numbness, loss of muscle coordination and problems with vision, speech, and bladder control).

Dextromethorphan is in a class of medications called central nervous system agents. The way it works in the brain to treat PBA is not known. Quinidine is in a class of medications called antiarrhythmics. When combined with dextromethorphan, quinidine works by increasing the amount of dextromethorphan in the body.

Side Effects Of Dextromethorphan and Quinidine

The combination of dextromethorphan and quinidine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • diarrhea
  • vomiting
  • gas
  • stomach pain
  • cough
  • dry eyes or mouth
  • weakness
  • muscle spasms
  • swelling of the hands, feet, ankles, or lower legs
  • frequent, painful, or difficult urination
  • cloudy or strong-smelling urine

Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately:

  • fever
  • unusual bleeding or bruising
  • muscle or joint pain
  • rash
  • swelling of the face, throat, tongue, or lips
  • swollen lymph nodes
  • hoarseness
  • difficulty breathing
  • lightheadedness
  • fainting
  • fast heartbeat

The combination of dextromethorphan and quinidine may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

Warnings & Precautions

Before taking dextromethorphan and quinidine:

  • tell your doctor and pharmacist if you are allergic to dextromethorphan, quinidine (Quinidex), quinine (Qualaquin), mefloquine (Lariam), any other medications, or any of the ingredients in combination dextromethorphan and quinidine capsules. Ask your pharmacist for a list of the ingredients.
  • tell your doctor if you are taking mefloquine (Lariam), pimozide (Orap), quinine (Qualaquin) thioridazine, or another product containing quinidine (Quinidex). Your doctor will probably tell you not to take dextromethorphan and quinidine if you are taking one or more of these medications.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: antidepressants including clomipramine (Anafranil), desipramine (Doxepin, Sinequan), fluoxetine (Prozac, Sarafem), nefazodone, and paroxetine (Paxil, Pexeva); aprepitant (Emend); clarithromycin (Biaxin, Prevpac); cough and cold medications containing dextromethorphan; cisapride; digoxin (Lanoxin, Digitek); erythromycin (E.E.S. E-Mycin, Erythrocin); fluconazole (Diflucan); itraconazole (Sporanox); ketoconazole (Nizoral); certain medications for human immunodeficiency virus (HIV) such as atazanavir (Reyataz), amprenavir (Agenerase), fosamprenavir (Lexiva), indinavir (Crixivan), nelfinavir (Viracept), ritonavir (Norvir, in Kaletra), and saquinavir (Invirase); medications for irregular heart beat such as amiodarone (Cordarone),diltiazem (Cardizem, Cartia, Tiazac, others), disopyramide (Norpace), dofetilide (Tikosyn), procainamide (Procanbid, Pronestyl),sotalol (Betapace), and verapamil (Calan, Covera, Isoptin, Verelan, in Tarka); medications for pain such as codeine, hydrocodone (in Hydrogesic, Lorcet, Lortab, Vicodin, Zydone, others), and methadone; moxifloxacin (Avelox); sparfloxacin (Zagam); and teliththromycin (Ketek). Also, tell your doctor or pharmacist if you are taking the following medications or have stopped taking them within the past two weeks: MAO inhibitors including isocarboxazid (Marplan), linezolid (Zyvox), phenelzine (Nardil), rasagiline (Azilect), selegiline (Eldepryl), and tranylcypromine (Parnate). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Many other medications may also interact with dextromethorphan and quinidine, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list.
  • tell your doctor if you have or have ever had the following conditions while taking quinidine, quinine, or mefloquine: decrease in the number of blood cells in your bone marrow, lupus (a condition in which the body attacks its own tissues causing damage and swelling), or hepatitis (swelling of the liver). Also, tell your doctor if you have or have ever had abnormal heart rhythms or heart failure. Your doctor will probably tell you not to takedextromethorphan and quinidine.
  • tell your doctor if you have or have ever had myasthenia gravis (a disorder of the nervous system that causes muscle weakness), a history of street drug use or prescription drug misuse, high blood pressure, a stroke, low levels of potassium or magnesium in your blood, or heart, kidney, or liver disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking the combination of dextromethorphan and quinidine, call your doctor.
  • if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking dextromethorphan and quinidine.
  • you should know that dextromethorphan and quinidine may make you dizzy. It is important to be careful to avoid falls while taking this medication.
  • ask your doctor about the safe use of alcoholic beverages while you are taking dextromethorphan and quinidine. Alcohol can make the side effects from this medication worse.

Dextromethorphan and Quinidine Dosage

The combination of dextromethorphan and quinidine comes as a capsule to take by mouth. It is usually taken with or without food once a day for 7 days. After 7 days, it is taken every 12 hours. Do not take more than 2 doses in a 24-hour period. Be sure to allow about 12 hours between each dose. Take dextromethorphan and quinidine at around the same time(s) every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take the combination of dextromethorphan and quinidine exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Your doctor may check from time to time to see if this medication is still needed to control your symptoms. Follow these directions carefully.


Keep all appointments with your doctor and the laboratory. Your doctor may order certain lab tests to check your body’s response to dextromethorphan and quinidine. Your doctor may also order an electrocardiogram (ECG; a test that measures the electrical activity in the heart) before and during your treatment.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.