Dextromethorphan and quinidine (Oral)
Medically reviewed by Drugs.com. Last updated on Jun 30, 2022.
Commonly used brand name(s)
In the U.S.
Available Dosage Forms:
Therapeutic Class: Central Nervous System Agent
Chemical Class: Quinidine
Uses for dextromethorphan and quinidine
Dextromethorphan and quinidine combination is used to treat a rare condition called pseudobulbar affect (PBA) or emotional incontinence. PBA is a nervous system disorder that is characterized by uncontrollable, sudden, and frequent episodes of crying or laughing.
Dextromethorphan and quinidine is available only with your doctor's prescription.
Before using dextromethorphan and quinidine
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For dextromethorphan and quinidine, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to dextromethorphan and quinidine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Appropriate studies have not been performed on the relationship of age to the effects of dextromethorphan and quinidine combination in the pediatric population. Safety and efficacy have not been established.
Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of dextromethorphan and quinidine combination in the elderly.
Studies in women suggest that this medication poses minimal risk to the infant when used during breastfeeding.
Interactions with medicines
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking dextromethorphan and quinidine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using dextromethorphan and quinidine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
Using dextromethorphan and quinidine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Aripiprazole Lauroxil
- Arsenic Trioxide
- Chloral Hydrate
- Dabigatran Etexilate
- Doxorubicin Hydrochloride Liposome
- Inotuzumab Ozogamicin
- Isavuconazonium Sulfate
- Methylene Blue
- Morphine Sulfate Liposome
- Nalidixic Acid
- Sirolimus Protein-Bound
- Sodium Phosphate
- Sodium Phosphate, Dibasic
- Sodium Phosphate, Monobasic
- Vincristine Sulfate Liposome
Using dextromethorphan and quinidine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Abiraterone Acetate
- Magnesium Carbonate
- Magnesium Hydroxide
- Magnesium Oxide
- Magnesium Trisilicate
Interactions with food/tobacco/alcohol
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using dextromethorphan and quinidine with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use dextromethorphan and quinidine, or give you special instructions about the use of food, alcohol, or tobacco.
- Grapefruit Juice
Other medical problems
The presence of other medical problems may affect the use of dextromethorphan and quinidine. Make sure you tell your doctor if you have any other medical problems, especially:
- Bone marrow problems caused by quinidine, quinine, or mefloquine, history of or
- Heart block without a pacemaker or
- Heart failure or
- Heart rhythm problems (e.g., congenital long QT syndrome, prolonged QT interval, or a history of torsade de pointes) or
- Hepatitis caused by quinidine, quinine, or mefloquine, history of or
- Lupus-like syndrome caused by quinidine, quinine, or mefloquine, history of or
- Thrombocytopenia (low platelets in the blood) caused by quinidine, quinine, or mefloquine, history of—Should not be used in patients with these conditions.
- Drug abuse or dependence, or history of—Dependence may be more likely to develop.
- Heart or blood vessel disease or
- Hypokalemia (low potassium in the blood) or
- Hypomagnesemia (low magnesium in the blood) or
- Hypertension (high blood pressure) or
- Stroke, history of—May increase risk for more serious side effects.
- Kidney disease, severe or
- Liver disease, severe—Higher blood levels of dextromethorphan and quinidine can occur, which increases the risk of serious side effects.
- Myasthenia gravis (severe muscle weakness)—Use with caution. May make this condition worse.
Proper use of dextromethorphan and quinidine
Take dextromethorphan and quinidine exactly as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered. To do so may increase the chance of side effects.
Grapefruits and grapefruit juice may increase the effects of dextromethorphan and quinidine combination by increasing the amount of dextromethorphan and quinidine in your body. You should not eat grapefruit or drink grapefruit juice while you are taking dextromethorphan and quinidine.
The dose of dextromethorphan and quinidine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of dextromethorphan and quinidine. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.
- For oral dosage form (capsules):
- For PBA or emotional incontinence:
- Adults—One capsule once a day for the first 7 days of treatment. Then on day 8 and onwards, dose should be two capsules per day, taken as one capsule every 12 hours. Each capsule contains 20 milligrams (mg) of dextromethorphan and 10 mg of quinidine.
- Children—Use and dose must be determined by your doctor.
- For PBA or emotional incontinence:
If you miss a dose of dextromethorphan and quinidine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.
Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.
Keep out of the reach of children.
Do not keep outdated medicine or medicine no longer needed.
Ask your healthcare professional how you should dispose of any medicine you do not use.
Precautions while using dextromethorphan and quinidine
It is very important that your doctor check your progress at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it. Blood tests may be needed to check for unwanted effects.
If your symptoms do not improve or if they become worse, check with your doctor.
Do not use dextromethorphan and quinidine together with other products containing quinidine, quinine (Qualaquin®), or mefloquine (Lariam®). You should not take dextromethorphan and quinidine if you are also using pimozide (Orap®), thioridazine (Mellaril®), or an MAO inhibitor (MAOI) such as Eldepryl®, Marplan®, Nardil®, or Parnate® within the past 14 days. Also, allow at least 14 days after stopping dextromethorphan and quinidine before starting an MAO inhibitor (MAOI).
Stop using dextromethorphan and quinidine and check with your doctor right away if you have the following symptoms while taking dextromethorphan and quinidine: black, tarry stools; bleeding gums; blood in the urine or stools; chills; fever; lightheadedness; nausea or vomiting; pinpoint red spots on the skin; or unusual bleeding or bruising.
Dextromethorphan and quinidine can cause changes in heart rhythms, such as a condition called QT prolongation. It may change the way your heart beats and cause fainting or serious side effects in some patients. Contact your doctor right away if you have any symptoms of heart rhythm problems, such as fast, pounding, or irregular heartbeats.
Dextromethorphan and quinidine may cause some people to become dizzy, trouble in controlling movements, or less alert than they are normally. Make sure you know how you react to dextromethorphan and quinidine before you drive, use machines, or do other jobs that require you to be alert and well-coordinated.
Make sure your doctor knows about all the other medicines you are using. Dextromethorphan and quinidine may cause a serious condition called serotonin syndrome when taken with medicine for depression (such as amitriptyline, clomipramine, doxepin, fluoxetine, imipramine, nortriptyline, Anafranil®, Elavil®, Prozac®, Sinequan®, or Tofranil®). Check with your doctor first before taking any other medicines.
Dextromethorphan and quinidine will add to the effects of alcohol and other CNS depressants (medicines that make you drowsy or less alert). Some examples of CNS depressants are antihistamines or medicine for hay fever, allergies, or colds; sedatives, tranquilizers, or sleeping medicine; prescription pain medicine or narcotics; other medicines for seizures (e.g., barbiturates); muscle relaxants; or anesthetics, including some dental anesthetics. Check with your medical doctor or dentist before taking any of the above while you are using dextromethorphan and quinidine.
Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.
Dextromethorphan and quinidine side effects
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur:
- Bladder pain
- bloating or swelling of the face, arms, hands, lower legs, or feet
- bloody or cloudy urine
- difficult, burning, or painful urination
- frequent urge to urinate
- general feeling of discomfort or illness
- joint pain
- loss of appetite
- lower back or side pain
- muscle aches and pains
- rapid weight gain
- runny nose
- sore throat
- tingling of the hands or feet
- trouble sleeping
- unusual tiredness or weakness
- unusual weight gain or loss
Get emergency help immediately if any of the following symptoms of overdose occur:
Symptoms of overdose
- Aggressive and violent behavior
- blurred vision
- change in color vision
- change in consciousness
- chest pain or discomfort
- confusion as to time, place, or person
- continuing ringing or buzzing or other unexplained noise in the ears
- decreased awareness or responsiveness
- difficulty seeing at night
- dizziness or lightheadedness
- dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
- double vision
- fast, pounding, or irregular heartbeat or pulse
- feeling of constant movement of self or surroundings
- hearing loss
- holding false beliefs that cannot be changed by fact
- inability to move the eyes
- increased blinking or spasms of the eyelid
- increased sensitivity of the eyes to sunlight
- irregular or slow heart rate
- loss of consciousness
- overactive reflexes
- poor coordination
- seeing double
- sensation of spinning
- severe sleepiness
- shakiness and unsteady walk
- shortness of breath
- sticking out of tongue
- talking or acting with excitement you cannot control
- trembling or shaking
- trouble with breathing, speaking, or swallowing
- uncontrolled eye movements
- uncontrolled twisting movements of the neck, trunk, arms, or legs
- unsteadiness, trembling, or other problems with muscle control or coordination
- unusual excitement, nervousness, or restlessness
- unusual facial expressions
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
- excess air or gas in the stomach or intestines
- full feeling
- lack or loss of strength
- passing gas
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
More about dextromethorphan / quinidine
- Side effects
- Drug interactions
- Dosage information
- During pregnancy
- Reviews (18)
- En español
- Drug class: miscellaneous central nervous system agents
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