Dextromethorphan and Quinidine

WHY is this medicine prescribed?

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; 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.

HOW should this medicine be used?

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.

Are there OTHER USES for this medicine?

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

What SPECIAL PRECAUTIONS should I follow?

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.
• some medications should not be taken with dextromethorphan and quinidine. Other medications may cause dosing changes or extra monitoring when taken with dextromethorphan and quinidine. Make sure you have discussed any medications you are currently taking or plan to take before starting dextromethorphan and quinidine with your doctor and pharmacist. Before starting, stopping, or changing any medications while taking dextromethorphan and quinidine, please get the advice of your doctor or pharmacist.
• 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).
• 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.

What SPECIAL DIETARY instructions should I follow?

Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medication.

Unless your doctor tells you otherwise, continue your normal diet.

What should I do IF I FORGET to take a dose?

Skip the missed dose and take the next dose at the regular time. Do not take a double dose to make up for a missed one. Be sure to allow 12 hours between doses.

What SIDE EFFECTS can this medicine cause?

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 heart beat

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

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (https://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

What should I know about STORAGE and DISPOSAL of this medication?

Keep this medication in the container it came in, tightly closed, and out of reach of children and pets. Store it at room temperature and away from excess heat and moisture (not in the bathroom).

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (https://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. https://www.upandaway.org

What should I do in case of OVERDOSE?

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at https://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

Symptoms of overdose may include:

• nausea
• vomiting
• diarrhea
• dizziness
• headache
• ringing in the ears
• blurred or double vision
• confusion
• changes in heart beat
• difficulty breathing
• loss of consciousness
• seizures
• changes in muscle reflexes
• loss of coordination
• unusual excitement
• abnormal thinking

What OTHER INFORMATION should I know?

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; 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.

This report on medications is for your information only, and is not considered individual patient advice. Because of the changing nature of drug information, please consult your physician or pharmacist about specific clinical use.

The American Society of Health-System Pharmacists, Inc. represents that the information provided hereunder was formulated with a reasonable standard of care, and in conformity with professional standards in the field. The American Society of Health-System Pharmacists, Inc. makes no representations or warranties, express or implied, including, but not limited to, any implied warranty of merchantability and/or fitness for a particular purpose, with respect to such information and specifically disclaims all such warranties. Users are advised that decisions regarding drug therapy are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and the information is provided for informational purposes only. The entire monograph for a drug should be reviewed for a thorough understanding of the drug's actions, uses and side effects. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information is not a substitute for medical care.

AHFS^® Patient Medication Information™. © Copyright, 2024. The American Society of Health-System Pharmacists^®, 4500 East-West Highway, Suite 900, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.

Selected Revisions: November 15, 2016.