currently [18:<7; when the urine is more alkaline, amount excreted unchanged in the urine decreases to as low as 5%. 1 Renal clearance involves both glomerular filtration and active tubular secretion, moderated by pH-dependent tubular reabsorption. 1 Half-life Following administration of dextromethorphan hydrobromide 30 mg and quinidine sulfate 30 mg in extensive metabolizers of CYP2D6 substrates, the elimination half-lives of dextromethorphan and quinidine were approximately 13 and 7 hours, respectively. 1 Special Populations Mild or moderate hepatic impairment: AUC, peak plasma concentrations, and clearance of dextromethorphan similar to those observed in healthy individuals. 1 Little effect on quinidine pharmacokinetics. 1 Severe hepatic impairment. Not studied; however, increases in dextromethorphan and/or quinidine concentrations likely. 1 Hepatic cirrhosis: Clearance of quinidine not affected; however, volume of distribution is increased, resulting in an increased elimination half-life of the drug. 1 Mild or moderate renal impairment: Little difference in the pharmacokinetics of quinidine or dextromethorphan compared with healthy individuals. 1 Severe renal impairment: Not studied; however, increases in dextromethorphan and/or quinidine concentrations likely. 1 Pharmacokinetics of dextromethorphan/quinidine not systematically evaluated in individuals> 65 years of age. 1 In a population pharmacokinetic analysis of patients receiving dextromethorphan hydrobromide 30 mg and quinidine sulfate 30 mg, similar pharmacokinetics were observed in individuals <65 years of age and those 65 years of age. 1 Pharmacokinetics of dextromethorphan/quinidine not studied in pediatric patients. 1 No apparent gender or racial differences in the pharmacokinetics of dextromethorphan/quinidine. 1 Stability Storage Oral Capsules 25 C (may be exposed to 15 30 C); protect from light and moisture. 1 Actions Dextromethorphan is the pharmacologically active ingredient in dextromethorphan/quinidine (Nuedexta ). 1 Dextromethorphan acts on the CNS as a potent σ 1 receptor agonist and a noncompetitive NMDA receptor antagonist. 1 2 3 4 5 6 10 Quinidine's main pharmacologic action in the fixed combination is to competitively inhibit CYP2D6, which increases and prolongs plasma concentrations of dextromethorphan. 1 2 3 4 5 6 Dextromethorphan also has serotonergic activity. 4 5 6 10 (See Serotonin Syndrome under Cautions.) Dextromethorphan's mechanism of action in the treatment of PBA is unknown, 1 4 5 6 10 but may involve σ 1 -mediated inhibition of neurotransmission of glutamate, which has an excitatory effect on neurons. 4 5 6 σ 1 Receptors are expressed principally in the brainstem and cerebellum, brain regions thought to be associated with emotional expression disorders. 6 Advice to Patients Risk of hypersensitivity reactions. 1 Importance of advising patients to seek immediate medical attention if they experience symptoms suggestive of a hypersensitivity reaction. 1 (See Contraindications and Thrombocytopenia and Other Hypersensitivity Reactions under Cautions.) Risk of cardiac effects. 1 Importance of patients informing their clinician of any personal or family history of QT c -interval prolongation. 1 Importance of advising patients to immediately contact their clinician if they feel faint or lose consciousness. 1 (See Contraindications and Cardiac Effects under Cautions.) Risk of dizziness. 1 Importance of advising patients to take precautions to reduce the risk of falls, especially if they have motor impairment affecting gait or a history of falls. 1 Importance of advising patients to take dextromethorphan/quinidine exactly as prescribed, with an interval of approximately 12 hours between doses and no more than 2 capsules (each containing dextromethorphan hydrobromide 20 mg and quinidine sulfate 10 mg) in a 24-hour period. 1 Importance of advising patients not to take a double dose if they miss a dose. 1 Importance of advising patients to contact clinician if symptoms of PBA persist or worsen. 1 Importance of women informing their clinician if they are or plan to become pregnant or plan to breast-feed. 1 Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs and dietary or herbal supplements, as well as any concomitant illnesses (e.g., QT c -interval prolongation or other cardiac disease). 1 Importance of informing patients of other important precautionary information. 1 (See Cautions.) Preparations Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details. Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations. Dextromethorphan Hydrobromide and quiNIDine Sulfate Routes Dosage Forms Strengths Brand Names Manufacturer Oral Capsules Dextromethorphan Hydrobromide 20 mg and Quinidine Sulfate 10 mg Nuedexta Avanir AHFS DI Essentials. Copyright 2017, Selected Revisions January 1, 2014. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814. Use is not currently included in the labeling approved by the US Food and Drug Administration. References 1. Avanir Pharmaceuticals, Inc. Nuedexta (dextromethorphan hydrobromide and quinidine sulfate) capsules prescribing information. Aliso Viejo, CA; 2011 Aug. 2. Pioro EP, Brooks BR, Cummings J et al. Dextromethorphan plus ultra low-dose quinidine reduces pseudobulbar affect. Ann Neurol . 2010; 68:693-702. [PubMed 20839238] 3. Brooks BR, Thisted RA, Appel SH et al. Treatment of pseudobulbar affect in ALS with dextromethorphan/quinidine: a randomized trial. Neurology . 2004; 63:1364-70. [PubMed 15505150] 4. Panitch HS, Thisted RA, Smith RA et al. Randomized, controlled trial of dextromethorphan/quinidine for pseudobulbar affect in multiple sclerosis. Ann Neurol . 2006; 59:780-7. [PubMed 16634036] 5. Anon. Dextromethorphan/quinidine (Nuedexta) for pseudobulbar affect. Med Lett Drugs Ther . 2011; 53:46-7. 6. Garnock-Jones KP. Dextromethorphan/quinidine: in pseudobulbar affect. CNS Drugs . 2011; 25:435-45. 7. Pioro EP. Current concepts in the pharmacotherapy of pseudobulbar affect. Drugs . 2011; 71: 1193-1207 [PubMed 21711063] 8. Pope LE, Schoedel KA, Bartlett C et al. A study of potential pharmacokinetic and pharmacodynamic interactions between dextromethorphan/quinidine and memantine in healthy volunteers. Clin Drug Invest . 2012; 32:e1-15. 9. AR Scientific, Inc. Qualaquin (quinine sulfate) capsules prescribing information. Philadelphia, PA; 2013 Apr. 10. Werling LL, Keller A, Frank JG et al. A comparison of the binding profiles of dextromethorphan, memantine, fluoxetine and amitriptyline: treatment of involuntary emotional expression disorder. Exp Neurol . 2007; 207:248-57. [PubMed 17689532] 11. Lilly USA, Inc. Quinidine gluconate solution prescribing information. Indianapolis, IN; 2012 Feb 24. Next Interactions Print this page Add to My Med List More about dextromethorphan/quinidine Side Effects During Pregnancy Dosage Information Drug Interactions Support Group En Español 13 Reviews Add your own review/rating Drug class: miscellaneous central nervous system agents Consumer resources Dextromethorphan and quinidine Dextromethorphan and quinidine (Advanced Reading) Professional resources Dextromethorphan and Quinidine (Wolters Kluwer) Other brands: Nuedexta Related treatment guides Pseudobulbar Affect> ] FEATURED: CAR-T Cell Therapy Overview Mechanism of Action KTE-C19 Studies KTE-C19 Cancer Targets Adverse Events Manufacturing Drug Status Rx Availability Prescription only C Pregnancy Category Risk cannot be ruled out N/A CSA Schedule Not a controlled drug Approval History Drug history at FDA Drug Class Miscellaneous central nervous system agents Related Drugs Pseudobulbar Affect Nuedexta , dextromethorphan / quinidine , More... 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