Dextromethorphan and Quinidine
Dextromethorphan and quinidine is a prescription combination used to treat pseudobulbar affect (PBA) — uncontrolled, involuntary episodes of laughing or crying caused by a neurological condition.
🧬 Where this information comes from Click to expand
The clinical label records used on this page are FDA-filed Structured Product Labeling (SPL) retrieved through openFDA. We identified 5 clinical label sets within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. Forms, routes, brands, labelers, strengths, and NDC product-record counts are built separately from matching FDA National Drug Code Directory records. The linked DailyMed document is a representative official source for verification, not the page’s only clinical source. View the linked label on DailyMed →
📖 Dextromethorphan and Quinidine: Patient Information Guide
A plain-language walkthrough of Dextromethorphan and Quinidine — what it treats, how it works, how it’s taken, side effects, warnings and interactions. Tap any section to expand it.
🎯What it's used for▾
Dextromethorphan and quinidine is a combination oral capsule indicated for one specific condition across all supported products.
- Pseudobulbar affect (PBA): Nuedexta, Dextromethorphan hydrobromide and quinidine sulfate capsules, and Dextromethorphan Hydrobromide and Quinidine Sulphate capsules are all approved to treat PBA — a neurological condition marked by involuntary, sudden, and frequent episodes of laughing and/or crying that do not match a person's actual emotional state. PBA occurs as a secondary condition to underlying neurological diseases such as ALS or MS, among others, and is distinct from general emotional instability tied to neurological illness.
⚙️How it works▾
Dextromethorphan is the therapeutically active ingredient: it blocks NMDA receptors (a type of brain signaling receptor) and activates sigma-1 receptors, both of which are thought to play a role in PBA — though the exact mechanism isn't fully understood. Quinidine's job in this combination is purely pharmacological: it inhibits the liver enzyme CYP2D6, which would otherwise break dextromethorphan down too quickly. By slowing that breakdown, quinidine allows dextromethorphan to reach and maintain the blood levels needed for a therapeutic effect — something that couldn't be achieved with dextromethorphan alone at safe doses.
💊How it's taken▾
All capsule forms of dextromethorphan and quinidine are taken by mouth. The starting dose is one capsule once daily for the first 7 days; from day 8 onward, the maintenance dose is one capsule every 12 hours (twice a day). The capsules can be taken with or without food. Your prescriber will reassess periodically whether continued treatment is still needed, since PBA sometimes improves on its own over time.
🤒Side effects — in detail▾
The most common side effects reported in clinical trials include:
- Diarrhea
- Dizziness
- Cough
- Vomiting
- Weakness or fatigue (asthenia)
- Swelling in the legs or feet (peripheral edema)
- Urinary tract infection
- Flu-like symptoms (influenza)
- Elevated liver enzyme (gamma-glutamyltransferase)
- Gas (flatulence)
Serious reactions — including dangerous drops in platelet count (thrombocytopenia), liver inflammation (hepatitis), heart rhythm problems, and serotonin syndrome — require prompt medical attention. Stop the medication and call your doctor right away if you notice unusual bleeding, jaundice, fainting, irregular heartbeat, or symptoms like agitation, fever, or muscle twitching.
⚠️Warnings & precautions▾
- Thrombocytopenia (dangerous drop in platelets): Quinidine can trigger an immune response that destroys platelets, potentially leading to severe or fatal bleeding. Stop the medication immediately if this occurs and do not restart it. Cross-sensitivity with quinine and mefloquine is possible.
- Hepatitis: Liver inflammation has been reported, usually in the first few weeks. Fever and thrombocytopenia may also be present. Most cases resolve when the medication is stopped.
- QT prolongation and heart rhythm risk: This medication can prolong the QT interval in a dose-dependent way, raising the risk of a dangerous arrhythmia called torsades de pointes. An ECG should be done at baseline and 3–4 hours after the first dose in patients at elevated risk, including those taking QT-prolonging drugs or CYP3A4 inhibitors, or those with left ventricular hypertrophy or dysfunction. Correct low potassium or magnesium before starting.
- Serotonin syndrome: When combined with SSRIs or tricyclic antidepressants, there is a risk of serotonin syndrome — a potentially serious condition involving agitation, rapid heartbeat, high temperature, and muscle twitching. Seek immediate care if symptoms appear.
- Dizziness and fall risk: About 10% of patients in controlled trials experienced dizziness. Take precautions, especially if you already have difficulty with balance or walking.
- CYP2D6 drug interactions: Quinidine inhibits the CYP2D6 enzyme, which processes many other medications. This can cause other drugs to build up to higher-than-expected levels or prevent prodrugs (like codeine) from being activated. Review all medications with your prescriber.
🔀What it interacts with▾
This medication has several important drug interactions, mainly because quinidine blocks the CYP2D6 liver enzyme and affects heart rhythm:
- MAOIs: Absolutely contraindicated — combining these can cause serious or fatal serotonin syndrome. Wait at least 14 days after stopping an MAOI before starting, and at least 14 days after stopping this medication before starting an MAOI.
- Thioridazine or pimozide: Contraindicated — these drugs both prolong QT and are processed by CYP2D6, creating a compounded risk of dangerous heart arrhythmia.
- SSRIs (e.g., fluoxetine) and tricyclic antidepressants: Increase the risk of serotonin syndrome; use with caution and monitor closely.
- Desipramine: Levels can rise approximately 8-fold — dose reduction is required if used together.
- Paroxetine: Levels can roughly double — consider starting at a lower dose and monitor.
- Digoxin: Levels can nearly double because quinidine inhibits P-glycoprotein; monitor digoxin levels closely and reduce the dose as needed.
- Other quinidine, quinine, or mefloquine products: Must not be combined with this medication.
- CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin, ritonavir, grapefruit juice): Can increase quinidine levels and QT-prolongation risk; an ECG may be needed.
- Alcohol and CNS depressants: Use with caution — additive effects on the central nervous system are possible.
This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.
📋Before taking it▾
- Do not take if you have a prolonged QT interval, congenital long QT syndrome, a history suggesting torsades de pointes, or heart failure — these are contraindications.
- Do not take if you have complete heart block (AV block) without a pacemaker, or if you are at high risk of developing complete AV block.
- Do not take if you have had an immune reaction (such as thrombocytopenia, hepatitis, bone marrow suppression, or a lupus-like reaction) to quinidine, quinine, or mefloquine.
- Do not take if you have a known allergy to dextromethorphan (e.g., rash or hives).
- Do not use with MAOIs or within 14 days of stopping one.
- Pregnancy: Animal studies showed developmental harm including birth defects and embryo loss. There are no adequate human studies. Discuss the risks with your doctor.
- Breastfeeding: Quinidine passes into breast milk. The effect on nursing infants is not fully known. Talk to your doctor about the benefits and risks.
- Children: Safety and effectiveness in patients under 18 have not been established.
- Older adults: Use with caution; dose selection should be conservative, given the higher likelihood of reduced kidney, liver, or heart function and multiple medications.
- Kidney or liver impairment: Dose adjustment is not required for mild-to-moderate impairment, but caution is warranted — drug levels may increase significantly in severe impairment.
- If you are a CYP2D6 poor metabolizer (your body naturally can't process this enzyme well), talk to your doctor — quinidine's main benefit may not apply to you, but its risks still do.
🚑If you take too much▾
An overdose of dextromethorphan and quinidine can cause symptoms including nausea, dizziness, vomiting, confusion, blurred vision, hearing changes, and — most seriously — dangerous heart rhythm problems (including torsades de pointes) and low blood pressure from the quinidine component, as well as seizures, respiratory depression, or stupor from excess dextromethorphan. Because quinidine slows the breakdown of dextromethorphan, overdose effects may be more severe or last longer than with dextromethorphan alone. Seek emergency medical care immediately if an overdose is suspected.
📡Pharmacodynamics — effects in the body▾
This medication causes a measurable, dose-dependent prolongation of the QTc interval — an electrical marker of how long it takes the heart to recharge between beats. At the recommended dose, the average QTc increase is modest (around 6–7 milliseconds), but at higher-than-recommended doses, the increase is larger. QT prolongation raises the risk of a specific type of dangerous heart arrhythmia called torsades de pointes, and this risk grows as the degree of QT lengthening increases. This effect is why the medication carries important heart-related contraindications and monitoring requirements.
🔬Pharmacokinetics — how your body processes it▾
After taking the capsule, dextromethorphan reaches peak blood levels in approximately 3 to 4 hours, and quinidine peaks in about 1 to 2 hours. Because quinidine blocks the CYP2D6 enzyme that would otherwise break down dextromethorphan rapidly, taking both together results in roughly 20 times more dextromethorphan in the bloodstream than dextromethorphan taken alone. Dextromethorphan has an elimination half-life of approximately 13 hours (the time it takes for blood levels to fall by half), while quinidine's half-life is approximately 7 hours. Both ingredients are processed primarily by the liver, and food does not significantly affect how much of either is absorbed, so the capsules can be taken with or without meals.
📦How to store it▾
Store dextromethorphan hydrobromide and quinidine sulfate capsules at 20° to 25°C (68° to 77°F); excursions permitted to 15° to 30°C (59° to 86°F) . Protect from light and moisture.
📄 Written from Dextromethorphan and Quinidine’s FDA-approved label information, summarized in plain language with AI, and reviewed by our pharmacy team before publication. Every point is grounded in that labeling — nothing is invented. How we use AI →
🩺 Pharmacist Counseling Corner
Quick, plain-English answers to the questions patients ask most about Dextromethorphan and Quinidine — the kind of thing our pharmacy team would talk through with you at the counter.
What exactly is pseudobulbar affect, and is this medication just for that? ▾
How long does it take to start working, and do I need to take it forever? ▾
I take an antidepressant. Is that a problem? ▾
What side effects should I actually expect, and when should I be worried? ▾
Can I drink alcohol while taking this medication? ▾
Is this medication safe during pregnancy or if I'm breastfeeding? ▾
Is Dextromethorphan and Quinidine available over the counter? ▾
When was Dextromethorphan and Quinidine first available? ▾
Who makes Dextromethorphan and Quinidine? ▾
💬 Answers drafted from Dextromethorphan and Quinidine’s FDA-approved label information, summarized in plain language with AI, and reviewed by our pharmacy team before publication. Grounded in that labeling — nothing is made up. How we use AI →
🧰 Keep exploring
💊 How Dextromethorphan and Quinidine comes
Dextromethorphan and Quinidine is available in 1 form. Different forms and brands can have different approved uses, doses, schedules, and directions. Follow the instructions for your exact product, and do not switch forms without guidance from your prescriber or pharmacist.
Capsule
How this form is used
- Dextromethorphan hydrobromide and quinidine sulfate capsules are indicated for the treatment of pseudobulbar affect (PBA)
- Dextromethorphan Hydrobromide and Quinidine Sulphate capsules are indicated for the treatment of pseudobulbar affect (PBA)
- Nuedexta is indicated for the treatment of pseudobulbar affect (PBA)
- Nuedexta, Dextromethorphan hydrobromide and quinidine sulfate, and Dextromethorphan Hydrobromide and Quinidine Sulphate capsules are all taken by mouth: one capsule once daily for the first 7 days, then one capsule every 12 hours (twice daily) from day 8 onward
- All capsule forms may be taken with or without food — food does not significantly affect how the medication is absorbed
- Your doctor will periodically reassess whether continued treatment is needed, as PBA can improve on its own in some patients
📊 Dextromethorphan and Quinidine across the U.S. market
How Dextromethorphan and Quinidine appears in the FDA’s National Drug Code Directory — including its dosage forms, strengths, brand names, manufacturers, and FDA-listed product records. These are directory records, not sales or prescription volume.
Share of FDA-listed product records by manufacturer — FDA National Drug Code Directory. Record counts are not sales or prescription volume.
📈 How widely Dextromethorphan and Quinidine is used
A general measure of how commonly Dextromethorphan and Quinidine is prescribed, based on Medicaid — one of the largest public drug programs. The figure below is prescriptions filled in Q1–Q4 2025, summed across every form and brand of the drug.
Think of this as a proxy for how widely Dextromethorphan and Quinidine is used, drawn from freely available public data. Medicaid is just one program — these numbers don’t include Medicare, other government coverage, or commercial and cash-pay prescriptions, so real-world use is higher than what’s shown here.
How commonly is Dextromethorphan and Quinidine prescribed? Of the 1,596 medications we measure, Dextromethorphan and Quinidine ranks #781 by Medicaid prescriptions — more than 51% of them.
Utilization by Dextromethorphan and Quinidine product
Pick a product to see its own Medicaid numbers. Each chip is one clinical product — a specific strength & dosage form as defined by RxNorm — with brand-name and generic versions combined.
dextromethorphan hydrobromide 20 MG / quinidine sulfate 10 MG Oral Capsule
Summed across the 2 of 7 listed NDC products with Medicaid activity — every brand and generic of this exact strength & form. RxNorm 1040054
Shares are of the Medicaid prescriptions shown here. Product grouping follows RxNorm (the National Library of Medicine’s drug terminology), so “one product” means one strength & dosage form regardless of manufacturer. Dollar figures are gross Medicaid reimbursement before mandatory rebates — rebates (often large, especially for brand-name drugs) are confidential, so actual net cost to Medicaid is lower than shown.
Source: Medicaid State Drug Utilization Data (CMS), aggregated by generic ingredient — summed across every NDC (all brands, strengths, salt forms and dosage forms) of Dextromethorphan and Quinidine, and across all states and both fee-for-service and managed-care claims. A general popularity signal; it excludes Medicare, commercial insurance and cash prescriptions, so it is not total U.S. use. Based on the 2 of 7 listed Dextromethorphan and Quinidine NDCs with Medicaid activity.
🔍 Compare Dextromethorphan and Quinidine products
A representative set of FDA-listed product records for Dextromethorphan and Quinidine — across manufacturers, strengths, and dosage forms, grouped by form with each product’s manufacturer and how the FDA approved it. The same medicine may be made and packaged by different companies, so a single drug can have many directory entries. (It’s also why a refill can look different — a new shape, color, or box — even though it contains the same medication.)
| Strength | Route | Manufacturer / Labeler | Category ⓘ | Details |
|---|---|---|---|---|
| 💊Capsule | ||||
| DEXTROMETHORPHAN HYDROBROMIDE 20 mg/1; QUINIDINE SULFATE 10 mg | Oral | Avanir Pharmaceuticals, Inc. | NDA | View NDC → |
| 20; 10 mg/1; mg | Oral | Avanir Pharmaceuticals, Inc. × 2 listings | NDA | View NDC → |
| DEXTROMETHORPHAN HYDROBROMIDE 20 mg/1; QUINIDINE SULFATE 10 mg | Oral | Camber Pharmaceuticals, Inc. | ANDA | View NDC → |
| DEXTROMETHORPHAN HYDROBROMIDE 20 mg/1; QUINIDINE SULFATE 10 mg | Oral | Golden State Medical Supply, Inc. | ANDA | View NDC → |
| DEXTROMETHORPHAN HYDROBROMIDE 20 mg/1; QUINIDINE SULFATE 10 mg | Oral | Otsuka America Pharmaceutical, Inc | NDA | View NDC → |
| 20; 10 mg/1; mg | Oral | Otsuka America Pharmaceutical, Inc | NDA | View NDC → |
| DEXTROMETHORPHAN HYDROBROMIDE 20 mg/1; QUINIDINE SULFATE 10 mg | — | Patheon Inc. | DRUG FOR FURTHER PROCESSING | View NDC → |
| DEXTROMETHORPHAN HYDROBROMIDE 20 mg/1; QUINIDINE SULFATE 10 mg | Oral | Sun Pharmaceutical Industries, Inc. | ANDA | View NDC → |
| DEXTROMETHORPHAN HYDROBROMIDE 20 mg/1; QUINIDINE SULFATE 10 mg | Oral | Teva Pharmaceuticals, Inc. | ANDA | View NDC → |
Showing 10 of 10 products — FDA National Drug Code Directory. See every product, package size and price: browse all 10 Dextromethorphan and Quinidine NDCs →
📈 What people report — real-world data (FDA FAERS)
After a medicine reaches the market, patients, doctors and drugmakers can send the FDA reports of problems they think may be linked to it. Here’s what’s been reported for Dextromethorphan and Quinidine — a signal of what to watch for, not proof the drug caused it.
Source: openFDA, from the FDA Adverse Event Reporting System (FAERS). These are voluntary reports — they don’t prove the drug caused the effect, and counts reflect how often something was reported, not how often it actually happens. Reports also often name the very problem the medicine is taken for — a common reason to file one is that the drug didn’t help — so for a pain reliever you may see “pain” high on the list; that points to why the report was filed, not to the drug causing the symptom. This counts every report that lists Dextromethorphan and Quinidine in any role, so the total runs higher than the FDA’s official dashboard, which counts only cases where the drug is the suspect. For the authoritative figures, see the FDA FAERS Public Dashboard. Always talk to your pharmacist or doctor.
🏛️ The road to your pharmacy
How Dextromethorphan and Quinidine went from FDA review to the pharmacy shelf — the key milestones in its regulatory journey.
Source: Drugs@FDA.
🚨 Recall history
A recall is when a specific batch of a medicine is pulled from the market — usually a manufacturing issue, not a problem with the drug itself. Class I is most serious, Class III least.
Source: openFDA drug enforcement (recall) reports.
📦 Supply & shortage status
Whether Dextromethorphan and Quinidine is in short supply in the U.S. right now, plus any shortage history the FDA has on record. A shortage usually reflects a manufacturing or demand issue — not a safety problem with the drug.
Source: openFDA, from the FDA Drug Shortages database.
🏷️ Sold under these brand names
🏭 Manufacturers & labelers
RxNorm drug class
Dextromethorphan and Quinidine belongs to the Uncompetitive N-methyl-D-aspartate Receptor Antagonist class.
Classified by RxNorm RxClass — the U.S. National Library of Medicine's standardized drug-classification service (Established Pharmacologic Class from the FDA, the ATC drug family from the WHO, and mechanism of action). Reference only, not medical advice.
🔬 Where this comes from
Core label, product, RxNorm, safety, and utilization data on this page come from the sources identified below. AI-written, editorial, and licensed sections are labeled separately.
How we combine label and product data
HelloPharmacist combines public FDA and NLM records; we don’t author the underlying clinical facts. We identified 5 FDA-filed SPL label sets within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. The representative label is the starting point for the displayed reference monograph; the 12 largest stored in-scope SPL records, which may include that representative, are compared section by section, and the longest available version of each section is retained. Forms, routes, brands, labelers, product-listed strengths, and product-record counts are aggregated separately from ingredient-matched FDA NDC Directory records; package records listed above are associated with the linked SPL; and the normalized concept hierarchy comes from NLM RxNorm.
For canonical ingredient pages, bounded product-attributed indication and administration excerpts may be added to the AI evidence, and the generator is instructed to preserve available product, brand, route, and form qualifiers instead of treating one label as universal. Where a section is identified as AI-written, its plain-language text is generated from bounded label evidence. New draft drug pages remain in the admin review queue before first publication. Avanir Pharmaceuticals, Inc. is the representative DailyMed label linked for verification and dates; it is not the sole source used for the page.
This is general education, not medical advice — always consult your doctor or pharmacist about your medications and any medical condition. For the exact wording of the linked representative label, view that label on DailyMed; some displayed composite sections may come from other in-scope SPL labels. Learn how we use AI and our data sources & update cadence.