Dextromethorphan / Quinidine Side Effects

Medically reviewed by Drugs.com. Last updated on Mar 27, 2024.

Applies to dextromethorphan / quinidine: oral capsule.

Serious side effects

Along with its needed effects, dextromethorphan/quinidine 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 while taking dextromethorphan / quinidine:

Less common side effects

• bladder pain
• bloating or swelling of the face, arms, hands, lower legs, or feet
• bloody or cloudy urine
• chills
• cough
• diarrhea
• difficult, burning, or painful urination
• fever
• frequent urge to urinate
• general feeling of discomfort or illness
• headache
• joint pain
• loss of appetite
• lower back or side pain
• muscle aches and pains
• nausea
• rapid weight gain
• runny nose
• shivering
• sore throat
• sweating
• tingling of the hands or feet
• trouble sleeping
• unusual tiredness or weakness
• unusual weight gain or loss
• vomiting

Get emergency help immediately if any of the following symptoms of overdose occur while taking dextromethorphan / quinidine:

Symptoms of overdose

• aggressive and violent behavior
• agitation
• blurred vision
• change in color vision
• change in consciousness
• chest pain or discomfort
• confusion
• confusion as to time, place, or person
• continuing ringing or buzzing or other unexplained noise in the ears
• decreased awareness or responsiveness
• depression
• difficulty seeing at night
• dizziness or lightheadedness
• dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
• double vision
• excitement
• fainting
• fast, pounding, or irregular heartbeat or pulse
• feeling of constant movement of self or surroundings
• hallucinations
• 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
• restlessness
• seeing double
• seizures
• sensation of spinning
• severe sleepiness
• shakiness and unsteady walk
• shivering
• shortness of breath
• sticking out of tongue
• sweating
• talking or acting with excitement you cannot control
• trembling or shaking
• trouble with breathing, speaking, or swallowing
• twitching
• 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

Other side effects

Some side effects of dextromethorphan / quinidine 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:

Less common side effects

• bloated
• excess air or gas in the stomach or intestines
• full feeling
• lack or loss of strength
• passing gas

For healthcare professionals

Applies to dextromethorphan / quinidine: oral capsule.

General adverse events

The most commonly reported adverse reactions (2% or greater incidence and greater than placebo) that led to treatment discontinuation were muscle spasticity, abdominal pain, asthenia, dizziness, muscle spasms, respiratory failure, and fall.^[Ref]

Gastrointestinal

• Very common (10% or more): Diarrhea (13%)
• Common (1% to 10%): Abdominal pain, vomiting, flatulence

Dextromethorphan:

• Postmarketing reports: Nausea, vomiting, stomach pain^[Ref]

Nervous system

• Very common (10% or more): Dizziness (10%)

Dextromethorphan:

• Postmarketing reports: Drowsiness, dizziness, nervousness, restlessness

Quinidine:

• Postmarketing reports: Convulsions, apprehension, ataxia, acute psychotic reactions (rare)^[Ref]

Cardiovascular

• Frequency not reported: QTc prolongation^[Ref]

Musculoskeletal

• Common (1% to 10%): Muscle spasticity, muscle spasms^[Ref]

Hepatic

• Common (1% to 10%): Increased gamma-glutamyltransferase^[Ref]

Respiratory

• Common (1% to 10%): Respiratory failure, cough^[Ref]

Other

• Common (1% to 10%): Asthenia, fall, peripheral edema

Quinidine:

• Postmarketing reports: Cinchonism^[Ref]

Cinchonism is usually a sign of chronic quinidine toxicity, but it may appear in sensitive patients after a single moderate dose of several hundred milligrams. It is characterized by nausea, vomiting, diarrhea, tinnitus headache, hearing loss, vertigo, blurred vision, diplopia, photophobia, confusion, and delirium.^[Ref]

Immunologic

• Common (1% to 10%): Influenza^[Ref]

Genitourinary

• Common (1% to 10%): Urinary tract infection^[Ref]

Ocular

Quinidine:

• Postmarketing reports: Mydriasis, disturbed color perception, night blindness, scotomata, optic neuritis, visual field loss, photosensitivity, keratopathy^[Ref]

Dermatologic

Quinidine:

• Postmarketing reports: Skin pigmentation abnormalities^[Ref]

Psychiatric

Quinidine:

• Postmarketing reports: Depression^[Ref]

Further information

Dextromethorphan/quinidine side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer