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dextromethorphan, combinations
N07XX59
Forms & Strengths
- Oral syrup: Dextromethorphan HBr / Quinidine sulfate 20 mg / 10 mg
- Oral capsules: Dextromethorphan HBr / Quinidine sulfate 20 mg / 10 mg
Adult Dosing
- Pseudobulbar affect: One capsule (20 mg/10 mg) orally once daily for 7 days, then increase to one capsule twice daily (approx. every 12 hours)
Pediatric Dosing
- Safety and efficacy in pediatric patients have not been established
Indications
- Treatment of pseudobulbar affect in patients with multiple sclerosis or amyotrophic lateral sclerosis (ALS)
Mechanism of Action
- Dextromethorphan acts as an uncompetitive NMDA receptor antagonist and sigma-1 agonist
- Quinidine acts as a CYP2D6 enzyme inhibitor to dramatically decrease the first-pass hepatic metabolism of dextromethorphan, significantly increasing its plasma concentrations and bioavailability
Contraindications
- Concomitant use with MAO inhibitors or within 14 days of stopping MAOIs
- Patients taking drugs metabolized by CYP2D6 or CYP2D6 substrates that prolong QT interval (e.g., thioridazine, pimozide)
- Patients with a history of quinidine-, quinine-, or mefloquine-induced thrombocytopenia, hepatitis, or hypersensitivity
- Patients with complete atrioventricular block without a pacemaker, or at high risk of heart block
- Concomitant use with drugs that prolong QT interval
Adverse Reactions
- Diarrhea
- Dizziness
- Cough
- Vomiting
- Asthenia
- Peripheral edema
- Urinary tract infection
- Increased gamma-glutamyltransferase
- Fall
- Somnolence
Drug Interactions
- CYP2D6 inhibitors and substrates (may alter concentrations)
- MAO inhibitors (risk of serotonin syndrome)
- Drugs that prolong the QT interval (risk of serious cardiac arrhythmias)
- CYP3A4 inducers (may decrease dextromethorphan/quinidine efficacy)
Curated Content: Needs Vetting Before Put to Clinical Use