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# Dextromethorphan / Guaifenesin (e.g., Robitussin DM, Mucinex DM)
## Overview
This combination product contains a cough suppressant (dextromethorphan) and an expectorant (guaifenesin).
## Primary Indications
* Temporary relief of cough associated with the common cold.
* Temporary relief of chest congestion and thinning of mucus.
## Adult Dosing
* **Dextromethorphan:** Typically 10 mg to 20 mg every 4 hours, or 30 mg every 6-8 hours. Maximum dose is generally 120 mg in 24 hours.
* **Guaifenesin:** Typically 200 mg to 400 mg every 4 hours, or 600 mg every 12 hours. Maximum dose is generally 2400 mg in 24 hours.
* **Combination Products:** Dosing varies by specific product formulation. Always refer to the product label. For example, a common formulation is Dextromethorphan 10 mg / Guaifenesin 100 mg per 5 mL. Usual adult dose: 10 mL to 20 mL every 4 hours as needed.
## Pediatric Dosing
Dosing varies significantly by age and specific product. **Consult product labeling carefully.**
* **Dextromethorphan:**
* Children 6 to <12 years: 5 mg to 10 mg every 4 hours, or 15 mg every 6-8 hours. Maximum dose 60 mg in 24 hours.
* Children <6 years: **Generally not recommended without physician guidance.** Some products may be approved for ages 2-5 years at reduced doses (e.g., 2.5 mg to 5 mg every 4 hours).
* **Guaifenesin:**
* Children 6 to <12 years: 100 mg to 200 mg every 4 hours, or 300 mg every 12 hours. Maximum dose 1200 mg in 24 hours.
* Children <6 years: **Generally not recommended without physician guidance.** Some products may be approved for ages 2-5 years at reduced doses (e.g., 50 mg to 100 mg every 4 hours).
* **Combination Products:** Pediatric dosing must be calculated based on the specific product formulation and the child's weight or age, following label instructions or physician guidance.
## Dose Adjustments
No specific dose adjustments are typically required for renal or hepatic impairment, but caution is advised.
## Contraindications
* Hypersensitivity to dextromethorphan or guaifenesin.
* Use within 14 days of MAO inhibitor therapy (dextromethorphan).
* Use in children younger than the age specified on the product label.
* Concurrent use with certain antidepressants (SSRIs, SNRIs, TCAs, MAOIs) can increase the risk of serotonin syndrome with dextromethorphan.
## Adverse Effects
* **Dextromethorphan:** Drowsiness, dizziness, nausea, vomiting, confusion, respiratory depression (at high doses). Can cause euphoria and hallucinations at supratherapeutic doses.
* **Guaifenesin:** Nausea, vomiting, dizziness, headache, rash.
## Key Drug Interactions
* **MAO Inhibitors, SSRIs, SNRIs, Tricyclic Antidepressants:** Increased risk of serotonin syndrome with dextromethorphan.
* **CNS Depressants (e.g., alcohol, sedatives, opioids):** Additive CNS depression.
## Monitoring
* Effectiveness of cough suppression and mucus expectoration.
* Signs of adverse effects, particularly drowsiness, confusion, and respiratory depression.
## Clinical Pearls
* Dextromethorphan is an NMDA receptor antagonist and sigma-1 receptor agonist.
* Guaifenesin works by increasing the volume and reducing the viscosity of secretions in the trachea and bronchi. Adequate hydration is important for guaifenesin's efficacy.
* Caution should be used in patients with chronic cough, persistent cough, or cough accompanied by excessive phlegm, as these may indicate a more serious condition requiring further evaluation.
* Many over-the-counter cold and cough products contain dextromethorphan. Be aware of potential accumulation and overdose when using multiple products.
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**Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Always verify current prescribing information, including dosing, contraindications, and warnings, with the most up-to-date product labeling or consult with a qualified healthcare professional before making any decisions related to patient care.
