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INTRODUCTION

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dextromethorphan/quinidine (deks-troe-meth-or-fan/kwin-i-deen)

Neudexta

Classification

Therapeutic: none assigned

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Indications
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Management of Pseudobulbar Affect (PSA), a mood disorder consisting of extremes of emotional lability (such as laughing fits followed by crying jags) seen in association with amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). Not effective for other forms of emotional lability.

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Action
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Dextromethorphan acts as an N-Methyl-D-aspartic acid (NMDA) receptor antagonist and sigma-1 agonist. Quinidine acts as an inhibitor of the CYP2D6 enzyme system, producing a marked ↑ in dextromethorphan blood levels. Therapeutic Effects: ↓ emotional lability.

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Adverse Reactions/Side Effects
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CNS: dizziness, weakness. Resp: cough. CV: peripheral edema, QT prolongation. GI: diarrhea, flatulence, hepatitis, ↑ liver enzymes, vomiting. Hemat: thrombocytopenia. Misc: hypersensitivity reactions including lupus-like syndrome.

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PHYSICAL THERAPY IMPLICATIONS

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Examination and Evaluation
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  • Monitor signs of hypersensitivity reactions, including lupus-like syndrome. Signs include increased blood pressure (BP), fever, joint pain, skin rashes, pulmonary symptoms (tightness in the throat and chest, wheezing, cough, dyspnea), and redness/irritation of the eye (uveitis). Notify physician promptly if these signs appear.

  • Assess heart rate, ECG, and heart sounds, especially during exercise (See Appendices G, H). Report any rhythm disturbances (QT prolongation) or symptoms of increased arrhythmias, including palpitations, chest discomfort, shortness of breath, fainting, and fatigue/weakness.

  • Assess peripheral edema using girth measurements, volume displacement, and measurement of pitting edema (See Appendix N). Report increased swelling in feet and ankles or a sudden increase in body weight due to fluid retention.

  • Watch for signs of thrombocytopenia, including bruising, nose bleeds, and bleeding gums. Report these signs to the physician.

  • Assess dizziness and weakness that might affect gait, balance, and other functional activities (See Appendix C). Report balance problems and functional limitations to the physician and nursing staff, and caution the patient and family/caregivers to guard against falls and trauma.

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Interventions
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  • Guard against falls and trauma (hip fractures, head injury, and so forth) caused by dizziness and weakness; implement fall prevention strategies (See Appendix E).

  • Help patient explore nonpharmacologic methods to reduce emotional lability, such as counseling, support groups, cognitive behavioral therapies, and so forth).

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Patient/Client-Related Instruction
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  • Advise patient about the likelihood of GI reactions such as vomiting, diarrhea, and flatulence. Instruct patient to report severe or prolonged GI problems, and also to report signs of liver toxicity, including yellow skin or eyes, abdominal pain, severe nausea and vomiting, fever, sore throat, malaise, weakness, and facial edema.

  • Instruct patient to report other problematic side effects such as severe or prolonged cough.

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Pharmacokinetics
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Absorption: Dextromethorphan—well absorbed following oral administration; quinidine—70–80% absorbed following oral administration.

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Distribution: quinidine—widely distributed, crosses placenta, enters breast milk.

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