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# Dextromethorphan / Guaifenesin (OTC Combination Product) ## Overview This is an over-the-counter combination product containing dextromethorphan, a cough suppressant, and guaifenesin, an expectorant. Various brand names exist, and product formulations can vary significantly in concentration and presence of other ingredients (e.g., decongestants, antihistamines). It is crucial to verify the exact active ingredients and their concentrations from the product packaging. ## Primary Indications * Symptomatic relief of cough associated with the common cold. * Aids in loosening mucus (guaifenesin) to make coughs more productive. ## Adult Dosing * **Dextromethorphan:** Typically 10 mg to 20 mg every 4 hours, OR 30 mg every 6-8 hours. **Maximum:** Varies by product, but generally do not exceed 120 mg per 24 hours. * **Guaifenesin:** Typically 200 mg to 400 mg every 4 hours, OR 600 mg to 1200 mg extended-release every 12 hours. **Maximum:** Varies by product, but generally do not exceed 2400 mg per 24 hours. * *Specific dosing and frequency are highly dependent on the individual product formulation. Always refer to the product label.* ## Pediatric Dosing * **Dextromethorphan:** * 6 to under 12 years: 5 mg to 10 mg every 4 hours, OR 15 mg every 6-8 hours. **Maximum:** Varies by product, generally do not exceed 60 mg per 24 hours. * Under 6 years: **Not recommended** without physician guidance due to increased risk of adverse effects and variability in metabolism. * **Guaifenesin:** * 6 to under 12 years: 100 mg to 200 mg every 4 hours, OR 300-600 mg extended-release every 12 hours. **Maximum:** Varies by product, generally do not exceed 1200 mg per 24 hours. * Under 6 years: **Not recommended** without physician guidance. * *Dosing in pediatric patients requires careful attention to product concentration and age/weight recommendations on the label. Combination products with other active ingredients (e.g., decongestants) may have different pediatric dosing guidelines.* ## Dose Adjustments * No specific dose adjustments are typically required for renal or hepatic impairment for these OTC agents, but caution and physician consultation are advised, especially in severe impairment, due to potential accumulation and increased adverse effects. ## Contraindications * Hypersensitivity to dextromethorphan or guaifenesin. * Concurrent use of monoamine oxidase inhibitors (MAOIs) or within 14 days of discontinuing an MAOI (for dextromethorphan). * Use in young children (under 4 or 6 years, depending on product labeling and regulatory guidance) for cough and cold products. * Patients with chronic bronchitis or persistent cough, unless directed by a physician. * Dextromethorphan containing products should be used with caution in patients with respiratory depression or conditions where cough suppression is inadvisable. ## Adverse Effects * **Dextromethorphan:** Dizziness, drowsiness, nausea, vomiting, confusion, hallucinations (rare, at high doses). Serotonin syndrome is a risk, especially with other serotonergic agents. * **Guaifenesin:** Nausea, vomiting, dizziness, headache, rash. ## Key Drug Interactions * **Dextromethorphan:** * **MAOIs:** Risk of hypertensive crisis and serotonin syndrome. * **SSRIs, SNRIs, Tricyclic Antidepressants, Triptans, Opioids (e.g., tramadol), linezolid, lithium, St. John's wort:** Increased risk of serotonin syndrome. * **CYP2D6 Inhibitors (e.g., fluoxetine, paroxetine, quinidine):** May increase dextromethorphan levels, potentially leading to toxicity. * **Alcohol:** Additive CNS depression. * **Guaifenesin:** Generally minimal significant drug interactions. Alcohol may increase the risk of GI upset. ## Monitoring * Effectiveness of cough suppression and mucus expectoration. * New or worsening symptoms (e.g., fever, shortness of breath, prolonged cough). * Signs of adverse effects, particularly CNS effects with dextromethorphan. * For patients with potential drug interactions, monitor for signs of serotonin syndrome. ## Clinical Pearls * Dextromethorphan's efficacy for cough suppression is comparable to placebo in some studies, but it is widely used. * Guaifenesin's effectiveness in loosening mucus is debated, but it is a common component of cough preparations. Adequate hydration is crucial for guaifenesin to be effective. * **Crucially, always check the product label for ALL active ingredients.** Many OTC cold products are multi-symptomatic and may contain decongestants (e.g., pseudoephedrine, phenylephrine), antihistamines (e.g., diphenhydramine, chlorpheniramine), or analgesics (e.g., acetaminophen, ibuprofen) which have their own dosing, interactions, and contraindications. * Avoid combining multiple dextromethorphan-containing products. * Do not use for prolonged periods without consulting a healthcare provider. *** **Disclaimer:** This information is intended for clinical use and is not a substitute for professional medical advice. Always consult the most current prescribing information, product monographs, or your drug information reference for complete and up-to-date details before making any treatment decisions. Verify dosing and safety information with the specific product being used.