Version May 2024
Agitation/aggression in Alzheimer disease (off-label use) (alternative agent): Oral: Dextromethorphan 20 mg/quinidine 10 mg once daily for 7 days, then increase to dextromethorphan 20 mg/quinidine 10 mg twice daily. The trial further increased the dosage after 14 days to dextromethorphan 30 mg/quinidine 10 mg twice daily; however, that dosage form is not commercially available in the United States (Ref).
Pseudobulbar affect: Oral: Dextromethorphan 20 mg/quinidine 10 mg once daily for 7 days, then increase to dextromethorphan 20 mg/quinidine 10 mg every 12 hours; reassess patient periodically to determine if continued use is necessary. Do not exceed dextromethorphan 40 mg/quinidine 20 mg in a 24-hour period.
Mild to moderate impairment (CrCl 30 to 80 mL/minute): No dosage adjustment necessary.
Severe impairment (CrCl <30 mL/minute): There are no dosage adjustments provided in the manufacturer’s labeling (has not been studied); however, increases in dextromethorphan/quinidine levels are likely to be observed.
Mild to moderate impairment (Child-Pugh class A or B): No dosage adjustment necessary; however, an increase in adverse reactions is observed with moderate impairment.
Severe impairment (Child-Pugh class C): There are no dosage adjustments provided in the manufacturer’s labeling (has not been studied); however, increases in dextromethorphan/quinidine levels are likely to be observed.
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified. Adverse reactions reported in adults. Also see individual agents.
>10%: Gastrointestinal: Diarrhea (13%)
1% to 10%:
Cardiovascular: Peripheral edema (5%)
Gastrointestinal: Flatulence (3%), vomiting (5%)
Genitourinary: Urinary tract infection (4%)
Hepatic: Increased gamma-glutamyl transferase (3%)
Infection: Influenza (4%)
Nervous system: Asthenia (5%), dizziness (10%)
Respiratory: Cough (5%)
Frequency not defined:
Cardiovascular: Prolonged QT interval on ECG
Gastrointestinal: Abdominal pain
Nervous system: Falling
Neuromuscular & skeletal: Muscle spasm, muscle spasticity
Respiratory: Respiratory failure
Hypersensitivity to dextromethorphan, quinidine, quinine, mefloquine, or any component of the formulation; concomitant use with quinidine or other medications containing quinidine, quinine, or mefloquine; history of quinine-, mefloquine-, or quinidine-induced thrombocytopenia, hepatitis, bone marrow depression, or lupus-like syndrome; concurrent administration with or within 2 weeks of discontinuing an MAO inhibitor; patients with prolonged QT interval, congenital QT syndrome, or history of torsade de pointes; patients with heart failure; concurrent use of drugs that prolong the QT interval and are metabolized by CYP2D6 (eg, pimozide, thioridazine); patients with complete atrioventricular (AV) block without an implanted pacemaker or patients at high risk of complete AV block
Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
Concerns related to adverse effects:
• Anticholinergic effects: May cause anticholinergic effects; use caution in patients with myasthenia gravis or other conditions which may be affected.
• Dizziness: May cause dizziness; use caution in patients with motor impairment or history of falls.
• Hepatotoxicity: Quinidine has been associated with hepatitis, including granulomatous hepatitis, occurring generally during the first few weeks of therapy. Most cases resolve when quinidine is discontinued.
• Hypersensitivity reactions: Agranulocytosis, angioedema, bronchospasm, hemolytic anemia, increased skeletal muscle enzymes, lymphadenopathy, myalgia, pneumonitis, rash, sicca syndrome, uveitis, vasculitis may be associated with use.
• Lupus-like syndrome: Lupus-like syndrome, with polyarthritis and sometimes a positive antinuclear antibody test, may occur with quinidine. Use is contraindicated in patients with quinidine-, quinine-, or mefloquine-induced lupus-like syndrome.
• Thrombocytopenia: Immune-mediated thrombocytopenia (severe or fatal) may be associated with quinidine use. Unless clearly not drug related, discontinue immediately; continued use may be associated with an increase in fatal hemorrhage. Thrombocytopenia generally resolves within a few days of discontinuation. Therapy should not be restarted in sensitized patients. Use is contraindicated in patients with prior history of immune-mediated thrombocytopenia associated with structurally related drugs (eg, quinine, mefloquine).
Concurrent drug therapy issues:
• High potential for interactions: Concomitant use of moderate or strong CYP3A4 inhibitors may increase quinidine levels and prolong the QTc interval. Quinidine inhibits CYP2D6; concomitant use with CYP2D6 substrates may cause an accumulation of concomitantly administered drug and/or reduce active metabolite formation, decreasing their safety and/or efficacy.
• QT prolonging agents: Use caution with medications which may further prolong the QT interval or cause cardiac arrhythmias. Dose-dependent QTc prolongation may occur. Monitor patients at risk following the first dose. Discontinue if arrhythmia occurs.
• Serotonin syndrome: Symptoms associated with serotonin syndrome such as agitation, confusion, hallucinations, hyper-reflexia, myoclonus, shivering, and tachycardia may occur with concomitant proserotonergic drugs (ie, SSRIs/SNRIs or triptans); especially with higher dextromethorphan doses. Discontinue if such reaction occurs.
Disease-related concerns:
• Cardiovascular disease: Use caution in patients with left ventricular hypertrophy or left ventricular dysfunction which are more common in patients with chronic hypertension, coronary artery disease or history of stroke; risk of QTc prolongation may be increased. Use is contraindicated in patients with prolonged QT interval, congenital QT syndrome, or history of torsade de pointes, patients with heart failure, complete AV block without an implanted pacemaker or patients at high risk of complete AV block. Correct hypokalemia or hypomagnesemia prior to therapy.
• Hepatic impairment: Safety and efficacy have not been established with severe hepatic impairment; increased serum concentrations may occur.
• Renal impairment: Safety and efficacy have not been established with severe renal impairment; increased serum concentrations may occur.
Special populations:
• CYP2D6 poor metabolizers: Dextromethorphan is metabolized by hepatic CYP2D6. Poor metabolizers of CYP2D6 may have exaggerated or prolonged effects of dextromethorphan. Increased risk may be seen with concomitant use of potent CYP2D6 inhibitors; use with caution (Abduljalil 2010; Jurica 2012; Sager 2014; Zhou 2009).
• Dementia: Has not shown to be safe or effective in other types of commonly occurring emotional labilities (eg, neurological disease or injury).
Other warnings/precautions:
• Appropriate use: Periodically reassess the need for treatment; spontaneous improvement of PBA may occur.
• Abuse/misuse: Patients with a history of drug abuse should be monitored closely for signs of abuse/misuse (eg, development of tolerance, increase in dose, drug-seeking behavior). Abuse of dextromethorphan may cause brain damage, cardiac arrhythmia, loss of consciousness, or death.
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Capsule, Oral:
Nuedexta: Dextromethorphan hydrobromide 20 mg and quinidine sulfate 10 mg
No
Capsules (Nuedexta Oral)
20-10 mg (per each): $31.48
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May be administered with or without food. Administer twice-daily doses every 12 hours.
Pseudobulbar affect: Treatment of pseudobulbar affect (PBA)
Agitation and/or aggression in Alzheimer disease
Nuedexta may be confused with Neulasta
Beers Criteria: Dextromethorphan and Quinidine is identified in the Beers Criteria as a potentially inappropriate medication to be used with caution in patients 65 years and older (independent of diagnosis or condition) due to limited efficacy in patients with behavioral symptoms of dementia and increased risk for mortality, falls, drug interactions, and QTc prolongation. Avoid use in patients with heart failure due to risk of exacerbation or fluid retention. Use of dextromethorphan and quinidine is still appropriate in the treatment of pseudobulbar affect (Beers Criteria [AGS 2023]).
Refer to individual components.
Note: Interacting drugs may not be individually listed below if they are part of a group interaction (eg, individual drugs within “CYP3A4 Inducers [Strong]” are NOT listed). For a complete list of drug interactions by individual drug name and detailed management recommendations, use the Lexicomp drug interactions program by clicking on the “Launch drug interactions program” link above.
Afatinib: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Afatinib. Management: If combined, administer the P-gp inhibitor simultaneously with, or after, the dose of afatinib. Monitor closely for signs and symptoms of afatinib toxicity and if the combination is not tolerated, reduce the afatinib dose by 10 mg. Risk D: Consider therapy modification
Aliskiren: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Aliskiren. Risk C: Monitor therapy
Amitriptyline: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Amitriptyline. CYP2D6 Inhibitors (Strong) may increase the serum concentration of Amitriptyline. Risk C: Monitor therapy
Amoxapine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Amoxapine. Risk C: Monitor therapy
Amphetamines: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Amphetamines. Management: Monitor for amphetamine toxicities (including serotonin syndrome) if used with a strong CYP2D6 inhibitor. Initiate amphetamine therapy at lower doses, monitor frequently, and adjust doses as needed. Discontinue amphetamines if serotoinin syndrome occurs. Risk C: Monitor therapy
ARIPiprazole: CYP2D6 Inhibitors (Strong) may increase the serum concentration of ARIPiprazole. Management: Aripiprazole dose reductions or avoidance are required for indications other than major depressive disorder. Dose adjustments vary based on formulation, initial starting dose, and the additional use of CYP3A4 inhibitors. See interact monograph for details Risk D: Consider therapy modification
ARIPiprazole Lauroxil: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of ARIPiprazole Lauroxil. Management: Decrease aripiprazole lauroxil dose to next lower strength if used with strong CYP2D6 inhibitors for over 14 days. No dose adjustment needed if using the lowest dose (441 mg) or if a CYP2D6 PM. Max dose is 441 mg if also taking strong CYP3A4 inhibitors. Risk D: Consider therapy modification
Artemether and Lumefantrine: May increase the serum concentration of CYP2D6 Substrates (High risk with Inhibitors). Risk C: Monitor therapy
Atomoxetine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Atomoxetine. Management: Initiate atomoxetine at a reduced dose (patients who weigh up to 70 kg: 0.5 mg/kg/day; adults or patients who weigh 70 kg or more: 40 mg/day) in patients receiving a strong CYP2D6 inhibitor. Increase to usual target dose after 4 weeks if needed. Risk D: Consider therapy modification
Benzhydrocodone: CYP2D6 Inhibitors (Strong) may decrease serum concentrations of the active metabolite(s) of Benzhydrocodone. Risk C: Monitor therapy
Berotralstat: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Berotralstat. Management: Decrease the berotralstat dose to 110 mg daily when combined with P-glycoprotein (P-gp) inhibitors. Risk D: Consider therapy modification
Bilastine: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Bilastine. Risk X: Avoid combination
Brexpiprazole: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Brexpiprazole. Management: Reduce brexpiprazole dose to 50% of usual with strong CYP2D6 inhibitors, reduce to 25% of usual if used with both a strong CYP2D6 inhibitor and a strong or moderate CYP3A4 inhibitor; these recommendations do not apply if treating major depressive disorder Risk D: Consider therapy modification
Broom: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Broom. Specifically, the concentrations of sparteine, a constituent of broom, may be increased. Risk C: Monitor therapy
Cardiac Glycosides: Quinidine (Non-Therapeutic) may increase the serum concentration of Cardiac Glycosides. Management: Measure cardiac glycoside serum concentrations before initiating treatment with quinidine. Reduce cardiac glycoside concentrations by either reducing the dose by 30% to 50% or by modifying the dosing frequency. Risk D: Consider therapy modification
Carvedilol: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Carvedilol. Risk C: Monitor therapy
Celiprolol: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Celiprolol. Risk C: Monitor therapy
Chlorpheniramine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Chlorpheniramine. Risk C: Monitor therapy
ClomiPRAMINE: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of ClomiPRAMINE. CYP2D6 Inhibitors (Strong) may increase the serum concentration of ClomiPRAMINE. Risk C: Monitor therapy
CloZAPine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of CloZAPine. Risk C: Monitor therapy
Codeine: CYP2D6 Inhibitors (Strong) may diminish the therapeutic effect of Codeine. These CYP2D6 inhibitors may prevent the metabolic conversion of codeine to its active metabolite morphine. Risk C: Monitor therapy
Colchicine: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Colchicine. Colchicine distribution into certain tissues (e.g., brain) may also be increased. Management: This combination is often contraindicated, but combined use may be permitted with dose adjustment and monitoring. Recommendations vary based on brand, indication, use of CYP3A4 inhibitors, and hepatic/renal function. See interaction monograph for details. Risk D: Consider therapy modification
CycloSPORINE (Systemic): P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of CycloSPORINE (Systemic). Risk C: Monitor therapy
CYP2D6 Inhibitors (Moderate): May increase the serum concentration of Dextromethorphan. Risk C: Monitor therapy
CYP2D6 Inhibitors (Strong): May increase the serum concentration of Dextromethorphan. Risk C: Monitor therapy
CYP3A4 Inhibitors (Moderate): May increase the serum concentration of Quinidine (Non-Therapeutic). Risk C: Monitor therapy
CYP3A4 Inhibitors (Strong): May increase the serum concentration of Quinidine (Non-Therapeutic). Risk C: Monitor therapy
Dabigatran Etexilate: P-glycoprotein/ABCB1 Inhibitors may increase serum concentrations of the active metabolite(s) of Dabigatran Etexilate. Risk C: Monitor therapy
Dapoxetine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Dapoxetine. Risk C: Monitor therapy
Desipramine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Desipramine. Risk C: Monitor therapy
Deutetrabenazine: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Deutetrabenazine. Management: The total daily dose of deutetrabenazine should not exceed 36 mg with concurrent use of a strong CYP2D6 inhibitor. Risk D: Consider therapy modification
Dextromethorphan: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Dextromethorphan. Risk C: Monitor therapy
Digoxin: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Digoxin. Management: Measure digoxin serum concentrations before initiating treatment with these P-glycoprotein (P-gp) inhibitors. Reduce digoxin concentrations by either reducing the digoxin dose by 15% to 30% or by modifying the dosing frequency. Risk D: Consider therapy modification
Disulfiram: May enhance the adverse/toxic effect of Products Containing Ethanol. Management: Do not use disulfiram with dosage forms that contain ethanol. Risk X: Avoid combination
Doxepin (Systemic): CYP2D6 Inhibitors (Strong) may increase the serum concentration of Doxepin (Systemic). Risk C: Monitor therapy
Doxepin (Topical): CYP2D6 Inhibitors (Strong) may increase the serum concentration of Doxepin (Topical). Risk C: Monitor therapy
DOXOrubicin (Conventional): CYP2D6 Inhibitors (Strong) may increase the serum concentration of DOXOrubicin (Conventional). Risk X: Avoid combination
DOXOrubicin (Conventional): P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of DOXOrubicin (Conventional). Risk X: Avoid combination
DOXOrubicin (Liposomal): P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of DOXOrubicin (Liposomal). Risk C: Monitor therapy
DULoxetine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of DULoxetine. Risk C: Monitor therapy
Edoxaban: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Edoxaban. Risk C: Monitor therapy
Eliglustat: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Eliglustat. Management: Eliglustat dose is 84 mg daily with CYP2D6 inhibitors. Use is contraindicated (COI) when also combined with strong CYP3A4 inhibitors. When also combined with a moderate CYP3A4 inhibitor, use is COI in CYP2D6 EMs or IMs and should be avoided in CYP2D6 PMs. Risk D: Consider therapy modification
Etoposide: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Etoposide. Risk C: Monitor therapy
Etoposide Phosphate: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Etoposide Phosphate. Risk C: Monitor therapy
Everolimus: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Everolimus. Risk C: Monitor therapy
Fenfluramine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Fenfluramine. Management: Limit fenfluramine dose to 20 mg/day without concurrent stiripentol or to 17 mg/day with concomitant stiripentol and clobazam when used with a strong CYP2D6 inhibitor. Risk D: Consider therapy modification
Fesoterodine: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Fesoterodine. Risk C: Monitor therapy
FluPHENAZine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of FluPHENAZine. Risk C: Monitor therapy
FluvoxaMINE: CYP2D6 Inhibitors (Strong) may increase the serum concentration of FluvoxaMINE. Risk C: Monitor therapy
Galantamine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Galantamine. Risk C: Monitor therapy
Gefitinib: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Gefitinib. Risk C: Monitor therapy
Glecaprevir and Pibrentasvir: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Glecaprevir and Pibrentasvir. Risk C: Monitor therapy
HYDROcodone: CYP2D6 Inhibitors (Strong) may decrease serum concentrations of the active metabolite(s) of HYDROcodone. Specifically, concentrations of hydromorphone may be decreased. Risk C: Monitor therapy
Iloperidone: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Iloperidone. Specifically, concentrations of the metabolite P88 may be increased. CYP2D6 Inhibitors (Strong) may decrease serum concentrations of the active metabolite(s) of Iloperidone. Specifically, concentrations of the metabolite P95 may be decreased. CYP2D6 Inhibitors (Strong) may increase the serum concentration of Iloperidone. Management: Reduce iloperidone dose by half when administered with a strong CYP2D6 inhibitor and monitor for increased iloperidone toxicities, including QTc interval prolongation and arrhythmias. Risk D: Consider therapy modification
Imipramine: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Imipramine. The concentrations of desipramine may be increased. CYP2D6 Inhibitors (Strong) may increase the serum concentration of Imipramine. Risk C: Monitor therapy
Indoramin: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Indoramin. Risk C: Monitor therapy
Lapatinib: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Lapatinib. Risk C: Monitor therapy
Larotrectinib: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Larotrectinib. Risk C: Monitor therapy
Lefamulin: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Lefamulin. Management: Avoid concomitant use of lefamulin tablets with P-glycoprotein/ABCB1 inhibitors. If concomitant use is required, monitor for lefamulin adverse effects. Risk D: Consider therapy modification
Lofepramine: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Lofepramine. The active metabolite of lofepramine is desipramine. Risk C: Monitor therapy
Lofexidine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Lofexidine. Risk C: Monitor therapy
Maprotiline: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Maprotiline. Risk C: Monitor therapy
Mefloquine: Quinidine (Non-Therapeutic) may enhance the adverse/toxic effect of Mefloquine. Risk X: Avoid combination
Memantine: NMDA Receptor Antagonists may enhance the adverse/toxic effect of Memantine. Risk C: Monitor therapy
Mequitazine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Mequitazine. Risk X: Avoid combination
Methadone: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Methadone. Risk C: Monitor therapy
Methotrimeprazine: Products Containing Ethanol may enhance the adverse/toxic effect of Methotrimeprazine. Specifically, a disulfiram-like reaction may occur and CNS depressant effects may be increased. Management: Avoid products containing alcohol in patients treated with methotrimeprazine. Risk X: Avoid combination
Metoclopramide: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Metoclopramide. Management: For gastroparesis: reduce metoclopramide dose to 5mg 4 times/day and limit to 20mg/day; nasal spray not recommended. For GERD: reduce metoclopramide dose to 5mg 4 times/day or to 10mg 3 times/day and limit to 30mg/day. Monitor for toxicity when combined. Risk D: Consider therapy modification
Metoprolol: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Metoprolol. Risk C: Monitor therapy
Mexiletine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Mexiletine. Risk C: Monitor therapy
Monoamine Oxidase Inhibitors: Dextromethorphan may enhance the serotonergic effect of Monoamine Oxidase Inhibitors. This may cause serotonin syndrome. Risk X: Avoid combination
Morphine (Systemic): P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Morphine (Systemic). Risk C: Monitor therapy
Nadolol: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Nadolol. Risk C: Monitor therapy
Naldemedine: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Naldemedine. Risk C: Monitor therapy
Naloxegol: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Naloxegol. Risk C: Monitor therapy
Nebivolol: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Nebivolol. Risk C: Monitor therapy
Nicergoline: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Nicergoline. Specifically, concentrations of the MMDL metabolite may be increased. CYP2D6 Inhibitors (Strong) may decrease serum concentrations of the active metabolite(s) of Nicergoline. Specifically, concentrations of the MDL metabolite may be decreased. Risk C: Monitor therapy
Nortriptyline: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Nortriptyline. Risk C: Monitor therapy
Oliceridine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Oliceridine. Risk C: Monitor therapy
Olmutinib: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Olmutinib. Risk C: Monitor therapy
Ornidazole: May enhance the adverse/toxic effect of Products Containing Ethanol. Specifically, a disulfiram-like reaction may occur. Risk X: Avoid combination
Parecoxib: May increase the serum concentration of Dextromethorphan. Risk C: Monitor therapy
PAZOPanib: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of PAZOPanib. Risk X: Avoid combination
Peginterferon Alfa-2b: May decrease the serum concentration of CYP2D6 Substrates (High risk with Inhibitors). Peginterferon Alfa-2b may increase the serum concentration of CYP2D6 Substrates (High risk with Inhibitors). Risk C: Monitor therapy
Perhexiline: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Perhexiline. Risk C: Monitor therapy
Perphenazine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Perphenazine. Risk C: Monitor therapy
Pimozide: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Pimozide. Risk X: Avoid combination
Pitolisant: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Pitolisant. Management: Reduce the pitolisant dose by 50% if a strong CYP2D6 inhibitor is initiated. For patients receiving strong CYP2D6 inhibitors, initiate pitolisant at 8.9 mg once daily and increase after 7 days to a maximum of 17.8 mg once daily. Risk D: Consider therapy modification
Pralsetinib: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Pralsetinib. Management: If this combo cannot be avoided, decrease pralsetinib dose from 400 mg daily to 300 mg daily; from 300 mg daily to 200 mg daily; and from 200 mg daily to 100 mg daily. Risk D: Consider therapy modification
Primaquine: CYP2D6 Inhibitors (Strong) may diminish the therapeutic effect of Primaquine. CYP2D6 Inhibitors (Strong) may decrease serum concentrations of the active metabolite(s) of Primaquine. Risk C: Monitor therapy
Propranolol: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Propranolol. Risk C: Monitor therapy
Protriptyline: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Protriptyline. Risk C: Monitor therapy
QT-prolonging Agents (Highest Risk): QT-prolonging Agents (Indeterminate Risk - Caution) may enhance the QTc-prolonging effect of QT-prolonging Agents (Highest Risk). Management: Monitor for QTc interval prolongation and ventricular arrhythmias when these agents are combined. Patients with additional risk factors for QTc prolongation may be at even higher risk. Risk C: Monitor therapy
QT-prolonging CYP2D6 Substrates: Quinidine (Non-Therapeutic) may enhance the QTc-prolonging effect of QT-prolonging CYP2D6 Substrates. Quinidine (Non-Therapeutic) may increase the serum concentration of QT-prolonging CYP2D6 Substrates. Risk X: Avoid combination
QuiNIDine: (Non-Therapeutic) may enhance the adverse/toxic effect of QuiNIDine. Risk X: Avoid combination
QuiNINE: Quinidine (Non-Therapeutic) may enhance the adverse/toxic effect of QuiNINE. Risk X: Avoid combination
Ranolazine: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Ranolazine. Risk C: Monitor therapy
Relugolix: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Relugolix. Management: Avoid coadministration of relugolix with oral P-gp inhibitors whenever possible. If combined, take relugolix at least 6 hours prior to the P-gp inhibitor and monitor patients more frequently for adverse reactions. Risk D: Consider therapy modification
Relugolix, Estradiol, and Norethindrone: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Relugolix, Estradiol, and Norethindrone. Management: Avoid use of relugolix/estradiol/norethindrone with P-glycoprotein (P-gp) inhibitors. If concomitant use is unavoidable, relugolix/estradiol/norethindrone should be administered at least 6 hours before the P-gp inhibitor. Risk D: Consider therapy modification
Repotrectinib: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Repotrectinib. Risk X: Avoid combination
RifAXIMin: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of RifAXIMin. Risk C: Monitor therapy
Rimegepant: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Rimegepant. Management: Avoid administration of another dose of rimegepant within 48 hours if given concomitantly with a P-glycoprotein (P-gp) inhibitor. Risk D: Consider therapy modification
RomiDEPsin: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of RomiDEPsin. Risk C: Monitor therapy
Saquinavir: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Saquinavir. Risk C: Monitor therapy
Secnidazole: Products Containing Ethanol may enhance the adverse/toxic effect of Secnidazole. Risk X: Avoid combination
Selective Serotonin Reuptake Inhibitors (Strong CYP2D6 Inhibitors): Dextromethorphan may enhance the serotonergic effect of Selective Serotonin Reuptake Inhibitors (Strong CYP2D6 Inhibitors). This could result in serotonin syndrome. Selective Serotonin Reuptake Inhibitors (Strong CYP2D6 Inhibitors) may increase the serum concentration of Dextromethorphan. Management: Consider alternatives to this drug combination. The dose of dextromethorphan/bupropion product should not exceed 1 tablet once daily. Monitor for signs and symptoms of serotonin syndrome/serotonin toxicity. Risk D: Consider therapy modification
Serotonergic Agents (High Risk): Dextromethorphan may enhance the serotonergic effect of Serotonergic Agents (High Risk). This could result in serotonin syndrome. Management: Monitor for signs and symptoms of serotonin syndrome/serotonin toxicity (eg, hyperreflexia, clonus, hyperthermia, diaphoresis, tremor, autonomic instability, mental status changes) when these agents are combined. Risk C: Monitor therapy
Sertindole: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Sertindole. Management: Consider alternatives to this combination when possible. If combined, consider using lower doses of sertindole and monitor the ECG closely for evidence of QTc interval prolongation. Risk D: Consider therapy modification
Silodosin: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Silodosin. Risk C: Monitor therapy
Sirolimus (Conventional): P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Sirolimus (Conventional). Management: Avoid concurrent use of sirolimus with P-glycoprotein (P-gp) inhibitors when possible and alternative agents with lesser interaction potential with sirolimus should be considered. Monitor for increased sirolimus concentrations/toxicity if combined. Risk D: Consider therapy modification
Sirolimus (Protein Bound): P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Sirolimus (Protein Bound). Risk X: Avoid combination
Tacrolimus (Systemic): P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Tacrolimus (Systemic). Risk C: Monitor therapy
Talazoparib: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Talazoparib. Risk C: Monitor therapy
Tamoxifen: CYP2D6 Inhibitors (Strong) may decrease serum concentrations of the active metabolite(s) of Tamoxifen. Specifically, strong CYP2D6 inhibitors may decrease the metabolic formation of highly potent active metabolites. Management: Avoid concurrent use of strong CYP2D6 inhibitors with tamoxifen when possible, as the combination may be associated with a reduced clinical effectiveness of tamoxifen. Risk D: Consider therapy modification
Tamsulosin: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Tamsulosin. Risk C: Monitor therapy
Tegaserod (Withdrawn from US Market): P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Tegaserod (Withdrawn from US Market). Risk C: Monitor therapy
Teniposide: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Teniposide. Risk C: Monitor therapy
Tenofovir Disoproxil Fumarate: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Tenofovir Disoproxil Fumarate. Risk C: Monitor therapy
Tetrabenazine: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Tetrabenazine. Specifically, concentrations of the active alpha- and beta-dihydrotetrabenazine metabolites may be increased. Management: Limit the tetrabenazine dose to 50 mg per day (25 mg per single dose) in patients taking strong CYP2D6 inhibitors. Risk D: Consider therapy modification
Thioridazine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Thioridazine. Risk X: Avoid combination
Timolol (Ophthalmic): CYP2D6 Inhibitors (Strong) may increase the serum concentration of Timolol (Ophthalmic). Risk C: Monitor therapy
Timolol (Systemic): CYP2D6 Inhibitors (Strong) may increase the serum concentration of Timolol (Systemic). Risk C: Monitor therapy
Tolterodine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Tolterodine. Risk C: Monitor therapy
Topotecan: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Topotecan. Risk X: Avoid combination
TraMADol: CYP2D6 Inhibitors (Strong) may decrease serum concentrations of the active metabolite(s) of TraMADol. CYP2D6 Inhibitors (Strong) may increase the serum concentration of TraMADol. Risk C: Monitor therapy
Trimipramine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Trimipramine. Risk C: Monitor therapy
Ubrogepant: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Ubrogepant. Management: Use an initial ubrogepant dose of 50 mg and second dose (at least 2 hours later if needed) of 50 mg when used with a P-gp inhibitor. Risk D: Consider therapy modification
Valbenazine: CYP2D6 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Valbenazine. Management: Reduce valbenazine dose to 40 mg once daily when combined with a strong CYP2D6 inhibitor. Monitor for increased valbenazine effects/toxicities. Risk D: Consider therapy modification
Venetoclax: P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of Venetoclax. Management: Reduce the venetoclax dose by at least 50% in patients requiring concomitant treatment with P-glycoprotein (P-gp) inhibitors. Resume the previous venetoclax dose 2 to 3 days after discontinuation of a P-gp inhibitor. Risk D: Consider therapy modification
VinCRIStine (Liposomal): P-glycoprotein/ABCB1 Inhibitors may increase the serum concentration of VinCRIStine (Liposomal). Risk X: Avoid combination
Vortioxetine: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Vortioxetine. Management: The vortioxetine dose should be reduced by 50% when used together with a strong CYP2D6 inhibitor. Following cessation of the strong CYP2D6 inhibitor, the vortioxetine dose should be returned to the normal level. Risk D: Consider therapy modification
Zuclopenthixol: CYP2D6 Inhibitors (Strong) may increase the serum concentration of Zuclopenthixol. Risk C: Monitor therapy
Grapefruit juice may increase levels of quinidine. Tonic water contains quinine. Management: Avoid grapefruit juice. Avoid tonic water.
Adverse events were observed in animal reproduction studies using this combination. See individual agents.
Quinidine is present in breast milk; excretion of dextromethorphan is not known.
According to the manufacturer, the decision to breastfeed during therapy should consider the risk of infant exposure, the benefits of breastfeeding to the infant, and benefits of treatment to the mother.
Avoid grapefruit juice.
QT interval at baseline and 3 to 4 hours after the first dose in patients at risk for QTc prolongation; potassium and magnesium prior to and during therapy; CBC, liver and renal function tests.
Dextromethorphan may relieve the symptoms of PBA by binding to sigma-1 receptors in the brain which may be involved in behavior, however the exact mechanism of action is not known. In the treatment of agitation and/or aggression in Alzheimer disease (off-label use), dextromethorphan may potentially relieve symptoms by several proposed mechanisms, including N-methyl-D-aspartase antagonism, sigma-1 receptor agonism, serotonin and norepinephrine reuptake inhibition, and nicotinic alpha-3-beta-4 receptor antagonism (Cummings 2015). However, the exact mechanism of action within this condition is not known.
Quinidine is used to block the rapid metabolism of dextromethorphan, thereby increasing serum concentrations. The dose of quinidine in this combination product provides serum concentrations 1% to 3% of those needed to treat cardiac arrhythmias.
Absorption: Bioavailability of dextromethorphan increased ~20-fold when administered with quinidine.
Protein binding: Dextromethorphan: 60% to 70%; Quinidine: 80% to 89%
Metabolism: Dextromethorphan: Hepatic via CYP2D6 to dextrorphan (active); Quinidine: Hepatic via CYP3A4 to 3-hydroxyquinidine (active) and other metabolites
Half-life elimination: Dextromethorphan: 13 hours in extensive metabolizers; Quinidine: 7 hours in extensive metabolizers
Time to peak: Dextromethorphan: 3 to 4 hours; Quinidine: 1 to 2 hours
Excretion: Urine (~20% as unchanged)
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