May 27, 2017
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Nuedexta Capsules

Side Effects


A total of 946 patients participated in four Phase 3 controlled and uncontrolled PBA studies and received at least one dose of the combination product of dextromethorphan/quinidine in various strengths at the recommended or higher than the recommended dose. Of those patients, 393 patients were exposed for at least 180 days and 294 patients were exposed for at least one year. Median exposure was 168 days.

Controlled trials enrolled only patients with either ALS or MS. Uncontrolled studies enrolled 136 patients with PBA secondary to a wide variety of underlying neurological conditions including stroke (45 patients) and traumatic brain injury (23 patients). Consequently, patients with other underlying neurologic diseases may experience other adverse reactions not described below.

Clinical Trials Experience

A 12-week, placebo-controlled study evaluated NUEDEXTA (dextromethorphan 20 mg/quinidine 10 mg) (N=107) and a 30 mg dextromethorphan/10 mg quinidine combination (N=110) compared to placebo (N=109). Approximately 60% of patients had ALS and 40% had MS. Patients were 25 to 80 years of age, with a mean age of approximately 51 years. Three (3) ALS patients in each drug treatment arm and 1 ALS patient in the placebo arm died during the 12-week placebo-control period. All deaths were consistent with the natural progression of ALS.

Adverse Reactions Leading To Discontinuation

The most commonly reported adverse reactions (incidence ≥ 2% and greater than placebo) that led to discontinuation with the 20 mg dextromethorphan/10 mg quinidine twice daily dose were muscle spasticity (3%), respiratory failure (1%), abdominal pain (2%), asthenia (2%), dizziness (2%), fall (1%), and muscle spasms (2%).

Most Common Adverse Reactions

Adverse drug reactions that occurred in ≥ 3% of patients receiving the 20 mg dextromethorphan/10 mg quinidine twice daily dose, and at an incidence of ≥ 2 times placebo in short-term clinical trials in ALS and MS are provided in Table 1.Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to the rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.

Table 1: Adverse Drug Reactions with an Incidence of ≥ 3% of Patients and ≥ 2x Placebo in NUEDEXTA-treated Patients by System-Organ Class and Preferred Term

Diarrhea 13 6
Dizziness 10 5
Cough 5 2
Vomiting 5 1
Asthenia 5 2
Peripheral edema 5 1
Urinary tract infection 4 1
Influenza 4 1
Increased gamma-
glutamyltransferase 3 0
Flatulence 3 1

Long-Term Exposure With NUEDEXTA

The experience in open-label clinical trials is consistent with the safety profile observed in the placebo-controlled clinical trials.

Safety Experience Of Individual Components

The following adverse reactions have been reported with the use of the individual components of NUEDEXTA, dextromethorphan and quinidine, from post-marketing experience. Because these reactions are reported voluntarily from a population of unknown size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.


Drowsiness, dizziness, nervousness or restlessness, nausea, vomiting, and stomach pain.


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

Convulsions, apprehension, and ataxia have been reported with quinidine therapy, but it is not clear that these were not simply the results of hypotension and consequent cerebral hypoperfusion in patients being treated for cardiovascular indications. Acute psychotic reactions have been reported to follow the first dose of quinidine, but these reactions appear to be extremely rare. Other adverse reactions occasionally reported with quinidine therapy include depression, mydriasis, disturbed color perception, night blindness, scotomata, optic neuritis, visual field loss, photosensitivity, keratopathy, and abnormalities of skin pigmentation.

Read the Nuedexta Capsules (dextromethorphan hydrobromide and quinidine sulfate capsules) Side Effects Center for a complete guide to possible side effects



Do not use NUEDEXTA with monoamine oxidase inhibitors (MAOIs) or in patients who have taken MAOIs within the preceding 14 days [see CONTRAINDICATIONS].

Drugs That Prolong QT And Are Metabolized By CYP2D6

Do not use with drugs that both prolong QT interval and are metabolized by CYP2D6 (e.g., thioridazine or pimozide) [see CONTRAINDICATIONS].

Drugs That Prolong QT And Concomitant CYP3A4 Inhibitors

Recommend ECG in patients taking drugs with NUEDEXTA that prolong the QT interval and in patients taking concomitant moderate or strong CYP3A4 inhibitors [see WARNINGS AND PRECAUTIONS].

SSRIs And Tricyclic Antidepressants

Use of NUEDEXTA with SSRIs or tricyclic antidepressants increases the risk of 'serotonin syndrome' [see WARNINGS AND PRECAUTIONS].

CYP2D6 Substrate

The co-administration of NUEDEXTA with drugs that undergo extensive CYP2D6 metabolism may result in altered drug effects, due to accumulation of parent drug and/or failure of metabolite formation [see WARNINGS AND PRECAUTIONS]. Therapy with medications that are primarily metabolized by CYP2D6 and that have a relatively narrow therapeutic index should be initiated at a low dose if a patient is receiving NUEDEXTA concurrently. If NUEDEXTA is added to the treatment regimen of a patient already receiving a drug primarily metabolized by CYP2D6, the need for a dose modification of the original medication should be considered. The extent to which CYP2D6 interactions may pose clinical problems will depend on the pharmacokinetics of the substrate involved.

In cases of prodrugs whose actions are mediated by the CYP2D6-produced metabolites (for example, codeine and hydrocodone, whose analgesic and antitussive effects appear to be mediated by morphine and hydromorphone, respectively), it may not be possible to achieve the desired clinical benefits in the presence of NUEDEXTA due to quinidine-mediated inhibition of CYP2D6. Consider use of alternative treatment with NUEDEXTA when clinically indicated.

Drug interactions with desipramine and paroxetine have been studied in controlled clinical trials with a higher dose combination of dextromethorphan/quinidine (dextromethorphan 30 mg/quinidine 30 mg) than NUEDEXTA; study results are described below. No other drug interactions with CYP2D6 substrates have been systematically investigated, although concomitant use of such drugs was allowed in clinical trials with NUEDEXTA and in clinical trials with higher dose formulations of dextromethorphan/quinidine.

Desipramine (CYP2D6 substrate)

The tricyclic antidepressant desipramine is metabolized primarily by CYP2D6. A drug interaction study was conducted between a higher combination dose of dextromethorphan (dextromethorphan 30 mg/quinidine 30 mg) and desipramine 25 mg. The combination dose of dextromethorphan/quinidine increased steady state desipramine levels approximately 8-fold. If NUEDEXTA and desipramine are prescribed concomitantly, the initial dose of desipramine should be markedly reduced. The dose of desipramine can then be adjusted based on clinical response; however, a dose above 40 mg/day is not recommended.

Paroxetine (CYP2D6 inhibitor and substrate)

When the combination dose of dextromethorphan 30 mg/quinidine 30 mg was added to paroxetine at steady state, paroxetine exposure (AUC0-24) increased by 1.7 fold and Cmax increased by 1.5 fold. Consideration should be given to initiating treatment with a lower dose of paroxetine if given with NUEDEXTA. The dose of paroxetine can then be adjusted based on clinical response; however, dosage above 35 mg/day is not recommended.


Quinidine is an inhibitor of P-glycoprotein. Concomitant administration of quinidine with digoxin, a Pglycoprotein substrate, results in serum digoxin levels that may be as much as doubled. Plasma digoxin concentrations should be closely monitored in patients taking NUEDEXTA concomitantly, and the digoxin dose reduced, as necessary.


As with any other CNS drug, caution should be used when NUEDEXTA is taken in combination with other centrally acting drugs and alcohol.

Drug Abuse And Dependence

NUEDEXTA is a low-affinity uncompetitive NMDA antagonist and sigma-1 receptor agonist that has not been systematically studied in animals or humans for its potential for abuse, tolerance, or physical dependence. However, NUEDEXTA is a combination product containing dextromethorphan and quinidine, and cases of dextromethorphan abuse have been reported, predominantly in adolescents.

While clinical trials did not reveal drug-seeking behavior, these observations were not systematic and it is not possible to predict on the basis of this experience the extent to which NUEDEXTA will be misused, diverted, and/or abused once marketed. Therefore, patients with a history of drug abuse should be observed closely for signs of NUEDEXTA misuse or abuse (e.g. development of tolerance, increases in dose, drug-seeking behavior).

Read the Nuedexta Capsules Drug Interactions Center for a complete guide to possible interactions

This monograph has been modified to include the generic and brand name in many instances.

Last reviewed on RxList: 5/9/2017

Side Effects

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