What is the dosage, frequency, and duration for polyTussin (dextromethorphan) in an adult?

PolyTussin Dosing for Adults

For adults, PolyTussin (containing dextromethorphan 15 mg per 5 mL) should be dosed at 1 teaspoonful (5 mL) every 4 to 6 hours, not exceeding 6 teaspoonfuls (30 mL) in 24 hours, for short-term symptomatic relief of acute cough lasting no more than 1-2 weeks. 1

Standard Dosing Regimen

Frequency and Amount:

• Adults and children ≥12 years: 1 teaspoonful (5 mL) every 4-6 hours 1
• Maximum daily dose: 6 teaspoonfuls (30 mL) in 24 hours 1
• This provides 15 mg dextromethorphan per dose, with a maximum of 90 mg daily 1

Duration of Treatment:

• Use for acute cough only, typically 1-2 weeks maximum 2, 3
• If cough persists beyond 1 week, stop use and consult a physician 1
• If cough persists beyond 3 weeks, discontinue and perform full diagnostic workup rather than continuing antitussive therapy 3

Important Clinical Considerations

Dosing Limitations:

• The standard over-the-counter dextromethorphan dose of 15 mg per 5 mL is often subtherapeutic 2, 3
• Maximum cough reflex suppression occurs at 60 mg dextromethorphan (which would require 20 mL of PolyTussin), though this exceeds the labeled single-dose recommendation 2, 4
• Caution with higher doses: PolyTussin contains additional active ingredients (dexbrompheniramine 2 mg and phenylephrine 7.5 mg per 5 mL) that may cause adverse effects at higher doses 1

When to Stop and Reassess:

• Beyond 14 days: Discontinue and evaluate for alternative diagnoses such as post-viral cough, pertussis, pneumonia, or chronic conditions 3
• Beyond 21 days (3 weeks): Cough is no longer "acute" and requires full diagnostic workup rather than continued antitussive therapy 3

Contraindications and Precautions

Do Not Use If: 1

• Currently taking or stopped within 2 weeks a monoamine oxidase inhibitor (MAOI) 1
• Have breathing problems such as emphysema or chronic bronchitis 1
• Have glaucoma 1
• Have enlarged prostate with urination difficulty 1
• Have chronic cough from smoking, asthma, or emphysema 1
• Have productive cough with excessive phlegm 1
• Have heart disease, high blood pressure, or thyroid disease 1

Stop Use and Seek Medical Attention If: 1

• Nervousness, dizziness, or sleeplessness occur 1
• Cough or nasal congestion persists for more than 1 week 1
• Cough recurs or is accompanied by fever, rash, or persistent headache 1
• New symptoms develop 1

Common Pitfalls to Avoid

• Do not prescribe for extended periods without reassessing the underlying cause 3
• Avoid using as a substitute for proper diagnosis when cough becomes chronic 3
• Do not exceed maximum daily dose due to risk of adverse effects from all three active ingredients 1
• Be aware of sedation risk: The antihistamine component (dexbrompheniramine) causes marked drowsiness; patients should avoid alcohol, driving, and operating machinery 1
• Monitor for drug interactions: The phenylephrine component may interact with other medications and affect blood pressure 1

Alternative Considerations

For more effective cough suppression without combination product risks:

• Consider dextromethorphan alone at 30-60 mg for better efficacy 2, 4
• Simple home remedies like honey and lemon may be equally effective for benign viral cough 2, 4
• Menthol inhalation provides acute but short-lived relief 2, 4