What are the safety precautions for consuming dextromethorphan (cough suppressant)?

Safety of Dextromethorphan

Dextromethorphan is safe and effective when used at recommended doses, but requires specific precautions regarding dosing, drug interactions, vulnerable populations, and abuse potential. 1, 2

Recommended Dosing and Administration

Maximum therapeutic efficacy occurs at 60 mg, which is higher than standard over-the-counter doses of 15-30 mg that are often subtherapeutic. 1, 3

FDA-Approved Dosing:

• Adults and children ≥12 years: 10 mL every 12 hours (maximum 20 mL/24 hours) 4
• Children 6 to <12 years: 5 mL every 12 hours (maximum 10 mL/24 hours) 4
• Children 4 to <6 years: 2.5 mL every 12 hours (maximum 5 mL/24 hours) 4
• Children <4 years: Do not use 4

Key Safety Point:

Exercise caution with combination preparations containing additional ingredients like acetaminophen or paracetamol, as higher doses of dextromethorphan may inadvertently lead to toxic doses of these co-ingredients. 1, 5, 6

Critical Drug Interactions

Avoid concurrent use with monoamine oxidase inhibitors (MAOIs) or selective serotonin reuptake inhibitors (SSRIs) due to risk of serotonin syndrome. 6, 2

Monitoring Requirements:

• If patient is taking MAOIs or SSRIs, implement poison center-initiated follow-up every 2 hours for 8 hours after dextromethorphan ingestion 6
• Watch for serotonin syndrome symptoms: hyperthermia (>104°F/40°C), agitation, seizures 6

The 2019 American Geriatrics Society Beers Criteria added dextromethorphan/quinidine combination to the "use with caution" category in older adults due to limited efficacy in dementia patients and increased risk of falls and drug-drug interactions. 7

Vulnerable Populations

Older Adults:

Use with caution in patients ≥65 years due to increased fall risk and potential drug interactions, particularly when combined with other CNS-active medications. 7

Patients with Cardiovascular Disease:

Dextromethorphan can be used for persistent cough in patients with end-stage cardiovascular disease when symptoms persist after addressing reversible causes. 7

Special Considerations:

• Some formulations contain sodium metabisulfite, which may cause allergic-type reactions in susceptible individuals 4
• Monitor diabetic patients more frequently when initiating dextromethorphan, and use sugar-free formulations 5

Contraindications and When NOT to Use

Do not use dextromethorphan in patients requiring assessment for pneumonia (tachycardia, tachypnea, fever, abnormal chest examination)—pneumonia must be ruled out first. 1

Central cough suppressants including dextromethorphan have limited efficacy for acute cough due to upper respiratory infection and are not recommended for this indication. 1

Red Flags Requiring Emergency Referral:

• Suicidal intent, intentional abuse, or suspected malicious intent (child abuse/neglect) 6
• More than mild symptoms (beyond infrequent vomiting or light somnolence) 6
• Ingestion >7.5 mg/kg body weight 6
• Coughing up blood, prolonged fever with malaise, or symptoms persisting >3 weeks 1, 3

Overdose and Toxicity Management

Overdose Thresholds:

• Ingestions of 5-7.5 mg/kg: Follow-up every 2 hours for 4 hours; refer to ED if more than mild symptoms develop 6
• Ingestions >7.5 mg/kg: Refer to emergency department 6
• Doses >1500 mg/day: Can induce PCP-like psychosis with delusions, hallucinations, and paranoia 8

Treatment Approach:

• Do not induce emesis 6
• Do not use activated charcoal at home 6
• For sedation/coma with respiratory depression: Consider naloxone in usual opioid overdose doses 6
• For seizures: Intravenous benzodiazepines 6
• For hyperthermia from serotonin syndrome: Benzodiazepines and external cooling 6

Abuse Potential

Abuse is the most significant safety hazard identified with dextromethorphan, particularly among adolescents seeking dissociative effects ("poor man's PCP"). 8, 2, 9

Abuse Patterns:

• Available in >140 over-the-counter preparations, making it readily accessible 8
• Not detected on standard urine drug screens 8
• Annual prevalence of abuse among 8th, 10th, and 12th graders decreased 35% from 2010-2015 following targeted mitigation efforts 10

Clinical Recognition:

Early identification and treatment of dextromethorphan abuse in younger adolescents may prevent broader substance abuse patterns. 9

Duration of Use

Dextromethorphan should only be used for short-term symptomatic relief (typically 10-14 days maximum). 1

Reassessment Algorithm:

• If cough persists >3 weeks: Mandatory reassessment to rule out post-viral cough, pertussis, pneumonia, or chronic conditions rather than continuing antitussive therapy 1
• Beyond 21 days: Cough is no longer "acute" and requires full diagnostic workup 1

Comparative Safety Profile

Dextromethorphan has superior safety compared to codeine and pholcodine, which offer no greater efficacy but have significantly worse adverse effect profiles (drowsiness, nausea, constipation, physical dependence). 1, 5, 3

Adverse drug reactions with dextromethorphan are infrequent and usually not severe, predominantly involving dose-related neurological, cardiovascular, and gastrointestinal disturbances. 2

Common Pitfalls to Avoid

• Prescribing standard OTC doses (15-30 mg) that are subtherapeutic instead of the effective 60 mg dose 1, 5
• Continuing dextromethorphan beyond 2-3 weeks without investigating underlying causes 1
• Failing to screen for concurrent MAOI/SSRI use before prescribing 6
• Not recognizing abuse potential in adolescent patients 8, 9
• Using dextromethorphan as substitute for proper diagnosis when cough becomes chronic 1