Generic Name and Formulations:
Dextromethorphan HBr 20mg, quinidine sulfate 10mg; capsules.
To treat pseudobulbar affect.
≥18yrs: 1 capsule daily for 7 days, then (starting on Day 8) 1 capsule every 12 hours. Reevaluate periodically.
<18yrs: not recommended.
Uncompetitive NMDA receptor antagonist and sigma-1 agonist + CYP2D6 inhibitor.
Concomitant quinidine, quinine, or mefloquine. History of quinine, mefloquine, or quinidine-induced thrombocytopenia, hepatitis, bone marrow depression, lupus-like syndrome. Within 14 days of MAOIs. Prolonged QT interval. Congenital long QT syndrome. History of torsades de pointes. Heart failure. Drugs that prolong QT interval and are CYP2D6 substrates (eg, thioridazine, pimozide). Complete AV block w/o pacemaker, or risk of complete AV block.
Discontinue if quinidine-related thrombocytopenia occurs (continued use may cause fatal hemorrhage); do not restart. Risk of QT prolongation and torsades de pointes (eg, concomitant drugs that prolong QT interval or that are strong or moderate CYP3A4 inhibitors, left ventricular hypertrophy, LVD): do ECG at baseline and 3–4 hours after 1st dose; reevaluate ECG if risk factors for arrhythmia (eg, electrolyte abnormality, bradycardia, family history of QT abnormality) change during treatment. Correct hypokalemia, hypomagnesemia before starting. Discontinue if arrhythmias occur. Myasthenia gravis. Consider genotyping for poor metabolizers of CYP2D6. Severe renal or hepatic impairment. Pregnancy (Cat. C). Nursing mothers.
See Contraindications. May cause serotonin syndrome with concomitant SSRIs (eg, fluoxetine) or TCAs (eg, clomipramine, imipramine). Accumulation of parent drug and/or failure of metabolite formation may decrease safety and/or efficacy of concomitant CYP2D6 substrates; adjust dose of CYP2D6 substrate or use alternative treatment. Concomitant desipramine, paroxetine: reduce dose of these drugs, adjust based on response. Monitor digoxin; may need to reduce dose. Additive CNS effects with alcohol.
GI upset, dizziness, cough, asthenia, peripheral edema, UTI, flu, increased gamma-glutamyltransferase, flatulence; thrombocytopenia, hypersensitivity, anticholinergic effects, hepatitis (discontinue if occurs).