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Dextromethorphan / Quinidine Dosage

Medically reviewed by Last updated on Aug 11, 2022.

Applies to the following strengths: 20 mg-10 mg

Usual Adult Dose for Pseudobulbar Affect

  • Initial Dose: Days 1 to 7: Dextromethorphan 20 mg-quinidine 10 mg orally once a day
  • Maintenance Dose: Day 8 and thereafter: Dextromethorphan 20 mg-quinidine 10 mg orally every 12 hours
  • Maximum dose: Dextromethorphan 40 mg-quinidine 20 mg orally per day

Comments: The need for continued treatment should be reassessed periodically as spontaneous improvement of PBA occurs in some patients.

Use: Treatment of Pseudobulbar Affect (PBA)

Renal Dose Adjustments

  • Mild Renal Impairment (CrCl 50 to 80 mL/min): No adjustment recommended.
  • Moderate Renal Impairment (CrCl 30 to 50 mL/min): No adjustment recommended.
  • Severe Renal Impairment (CrCl less than 30 mL/min): Data not available; however, increases in dextromethorphan and/or quinidine levels are likely to be observed.

Liver Dose Adjustments

  • Mild Hepatic Impairment (Child-Pugh A): No adjustment recommended.
  • Moderate Hepatic Impairment (Child-Pugh B): No adjustment recommended.
  • Severe Hepatic Impairment (Child-Pugh C): Data not available; however, increases in dextromethorphan and/or quinidine levels are likely to be observed.


Safety and efficacy have not been established in patients younger than 18 years.

Consult WARNINGS section for additional precautions.


Data not available

Other Comments

Administration Advice:

  • This drug can be taken without regard to meals.
  • There should be an approximate 12-hour interval between doses; more than 2 doses should not be taken in a 24-hour period.
  • A double dose should not be taken to account for a missed dose.

  • Cardiovascular: ECG (before treatment initiation and during therapy as clinically indicated), magnesium and potassium levels (prior to and during treatment)

Patient Advice:
  • Avoid eating grapefruit and drinking grapefruit juice and alcohol while taking this drug.
  • You may bleed more easily while taking this drug. Talk with your doctor about ways to avoid injury, such as using a soft toothbrush and electric razor.
  • This drug may cause side effects such as dizziness that can affect your ability to perform certain activities; avoid driving and activities such as operating machinery until you know how this drug affects you.
  • If you miss a dose, take it as soon as you remember. If it is close to the time for your next dose, skip the missed dose and take the next dose at your regular time.
  • Do not take 2 doses at the same time or extra doses.
  • This drug can interact with a variety of medications. Tell your doctor about all the medications you take, including prescription and over-the-counter drugs, vitamins, and dietary and herbal supplements.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.