Medically reviewed on January 29, 2018
What is dextromethorphan and quinidine?
Dextromethorphan affects the signals in the brain that trigger cough reflex and is generally used as a cough suppressant.
Quinidine affects the way that the heart beats and is generally used in people with certain heart rhythm disorders.
Dextromethorphan and quinidine is a combination medicine used to treat involuntary outbursts of crying or laughing in people with certain neurological disorders, including multiple sclerosis and amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease).
Dextromethorphan and quinidine may also be used for purposes not listed in this medication guide.
You should not use this medicine if you have heart failure, a serious heart condition called "AV block" (unless you have a pacemaker), or a history of Long QT syndrome or life-threatening heart rhythm disorder.
Do not use dextromethorphan and quinidine if you have used an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine, and others.
You also should not take dextromethorphan and quinidine if you are also taking mefloquine, quinidine, or quinine, or if you have ever had an allergic reaction or serious medical problem caused by taking any of these medications.
Some medicines can interact with dextromethorphan and quinidine and should not be used at the same time. Tell your doctor about all medicines you use, and those you start or stop using during your treatment with dextromethorphan and quinidine.
Before taking this medicine
You should not take this medicine if you are allergic to dextromethorphan or quinidine, or if you have:
a history of life-threatening heart rhythm disorder;
a serious heart condition called "AV block" (unless you have a pacemaker);
a history of Long QT syndrome; or
if you are also taking mefloquine, quinidine, or quinine.
Do not use dextromethorphan and quinidine if you have used an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine, and others. After you stop taking dextromethorphan and quinidine, you must wait at least 14 days before you start taking an MAOI.
You also should not take dextromethorphan and quinidine if you have ever had any of the following problems caused by taking mefloquine, quinidine, or quinine:
low levels of platelets in your blood;
bone marrow suppression; or
Some medicines can cause unwanted or dangerous effects when used with dextromethorphan and quinidine. Your doctor may need to change your treatment plan if you use any of the following drugs:
To make sure dextromethorphan and quinidine is safe for you, tell your doctor if you have:
an electrolyte imbalance (such as low levels of potassium or magnesium in your blood);
slow heartbeats or any type of heart rhythm disorder;
bladder obstruction or other urination problems; or
blockage in your digestive tract (stomach or intestines).
FDA pregnancy category C. It is not known whether dextromethorphan and quinidine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant while using this medication.
It is not known whether dextromethorphan and quinidine passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.
Do not give dextromethorphan and quinidine to anyone under 18 years old without medical advice.
How should I take dextromethorphan and quinidine?
Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.
Dextromethorphan and quinidine is usually started at a dose of 1 capsule per day for 7 days. After the first week you will take 1 capsule every 12 hours. Follow your doctor's instructions. Do not take more than 2 capsules in a 24-hour period.
You may take dextromethorphan and quinidine with or without food.
Your doctor will need to check your progress on a regular basis. This will help your doctor determine how long to treat you with dextromethorphan and quinidine. Your heart function may need to be checked using an electrocardiograph or ECG (sometimes called an EKG).
Store at room temperature away from moisture and heat.
What happens if I miss a dose?
Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.
What should I avoid while taking dextromethorphan and quinidine?
This medication may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert. Avoid getting up too fast from a sitting or lying position, or you may feel dizzy. Get up slowly and steady yourself to prevent a fall.
Ask a doctor or pharmacist before using any cough or cold medication. Dextromethorphan is contained in many combination medicines. Taking certain products together can cause you to get too much dextromethorphan. Check the label to see if a medicine contains dextromethorphan (Delsym, Robitussin Maximum Strength, Vicks 44, and others).
Dextromethorphan and quinidine side effects
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Stop using this medicine and call your doctor at once if you have:
headache with chest pain and severe dizziness or fainting;
fast or pounding heartbeats, fluttering in your chest;
easy bruising or bleeding (nosebleeds, bleeding gums);
pain or burning when you urinate;
lupus-like symptoms--joint pain or swelling with fever, headaches, confusion, chest pain, shortness of breath, skin sores, butterfly-shaped skin rash on your cheeks and nose, and numbness, cold feeling, or pale appearance of your fingers or toes;
Common side effects may include:
diarrhea, gas, vomiting;
swelling in your hands or feet;
dizziness, weakness; or
flu symptoms, cough.
Side effects such as dry mouth, constipation, and confusion may be more likely in older adults.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
See also: Side effects (in more detail)
What other drugs will affect dextromethorphan and quinidine?
Many drugs can interact with dextromethorphan and quinidine. Not all possible interactions are listed here. Tell your doctor about all your medications and any you start or stop using during treatment with dextromethorphan and quinidine, especially:
This list is not complete and many other drugs can interact with dextromethorphan and quinidine. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Give a list of all your medicines to any healthcare provider who treats you.
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
Copyright 1996-2018 Cerner Multum, Inc. Version: 1.04.
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