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# Dextromethorphan/Guaifenesin ## Overview This combination product contains a cough suppressant (dextromethorphan) and an expectorant (guaifenesin). ## Primary Indications Symptomatic relief of cough and chest congestion associated with the common cold, bronchitis, and other upper respiratory tract conditions. ## Adult Dosing * **Dextromethorphan:** 10-20 mg every 4 hours, or 30 mg every 6-8 hours. Maximum 120 mg/day. * **Guaifenesin:** 200-400 mg every 4 hours. Maximum 2400 mg/day. * *Specific dosing for combination products varies by formulation. Always check the product label.* ## Pediatric Dosing * **Dextromethorphan:** * 6-12 years: 5-10 mg every 4 hours, or 15 mg every 6-8 hours. Maximum 60 mg/day. * Under 6 years: Safety and efficacy not established for combination products. Consult product labeling or pediatrician. * **Guaifenesin:** * 6-12 years: 100-200 mg every 4 hours. Maximum 1200 mg/day. * Under 6 years: Safety and efficacy not established for combination products. Consult product labeling or pediatrician. * *Dosing for combination products in pediatrics requires careful attention to the specific formulation and age-appropriateness.* ## Dose Adjustments No specific dose adjustments are typically required for hepatic or renal impairment, but caution is advised, and lower doses may be considered. ## Contraindications * Hypersensitivity to dextromethorphan or guaifenesin. * Use with or within 14 days of MAOI therapy (for dextromethorphan). * Use in patients with persistent or chronic cough, such as that associated with asthma or emphysema, unless directed by a physician (due to potential for bronchodilation masking symptoms). ## Adverse Effects * **Dextromethorphan:** Dizziness, drowsiness, nausea, vomiting, constipation. Abuse potential exists at higher doses. Serotonin syndrome is a rare but serious risk, especially when combined with serotonergic agents. * **Guaifenesin:** Nausea, vomiting, stomach pain, dizziness, headache. ## Key Drug Interactions * **Dextromethorphan:** * MAO inhibitors: Risk of severe hypertension and serotonin syndrome. * SSRIs, SNRIs, tricyclic antidepressants, triptans, certain opioids (tramadol, fentanyl), lithium, St. John's wort: Increased risk of serotonin syndrome. * CYP2D6 inhibitors (e.g., fluoxetine, paroxetine, quinidine): May increase dextromethorphan levels, leading to increased toxicity. * **Guaifenesin:** Generally considered to have few significant drug interactions. ## Monitoring * Monitor for therapeutic effectiveness (cough suppression, mucus expectoration). * Monitor for adverse effects, particularly CNS effects with dextromethorphan and GI upset with guaifenesin. * Assess for signs of serotonin syndrome if concomitant serotonergic agents are used. ## Clinical Pearls * Adequate hydration is important to help guaifenesin thin mucus. * Combination products can lead to overuse or inappropriate dosing if individual components are needed at different strengths or frequencies. Carefully assess if both agents are truly indicated. * Dextromethorphan is an NMDA receptor antagonist and has abuse potential. Counsel patients on appropriate use and storage. * Guaifenesin's efficacy in thinning mucus is debated, but it remains a common component of cough and cold preparations. --- *This information is for educational purposes only and does not constitute medical advice. Always verify current prescribing information with official drug compendia or product labeling before making clinical decisions.*