What are the contraindications to Robitussin (dextromethorphan)?

Contraindications to Robitussin (Dextromethorphan)

Dextromethorphan has very few absolute contraindications, with the most critical being concurrent use with monoamine oxidase inhibitors (MAOIs), which can precipitate a dangerous serotonergic reaction. 1

Absolute Contraindications

MAOI Interaction

• Concurrent use with MAOIs or within 14 days of discontinuing MAOI therapy is contraindicated due to risk of serotonin syndrome, which can manifest as hyperthermia, agitation, confusion, cardiovascular instability, and potentially fatal outcomes 1
• This represents the most significant safety concern identified in adverse event reporting for dextromethorphan 1

Productive Cough

• Dextromethorphan should not be used when cough is productive and clearance of secretions is beneficial, as suppressing a productive cough can impair mucus clearance and potentially worsen respiratory conditions 2

Relative Contraindications and Cautions

Specific Clinical Scenarios Requiring Alternative Management

• Do not use in patients requiring assessment for pneumonia - if tachycardia (>100 bpm), tachypnea (>24 breaths/min), fever (>38°C), or abnormal chest examination findings are present, pneumonia must be ruled out first 3
• Avoid in cough with increasing breathlessness - assess for asthma or anaphylaxis instead 4
• Do not use when cough is accompanied by fever, malaise, or purulent sputum - these may indicate serious lung infection requiring specific treatment 4
• Contraindicated when significant hemoptysis or possible foreign body inhalation is present - these require specialist referral 4

Combination Product Concerns

• Exercise caution with higher doses of dextromethorphan in combination preparations that contain additional ingredients like paracetamol (acetaminophen), as this increases risk of unintentional overdose of the secondary ingredient 4, 2

Clinical Context for Appropriate Use

When Dextromethorphan Is NOT Recommended

• Acute cough due to upper respiratory infection (URI) - central cough suppressants including dextromethorphan have limited efficacy and are not recommended for this indication 3
• Routine use in acute bronchitis - not recommended due to inconsistent results, though may be offered for short-term symptomatic relief in select cases 2

Abuse Potential

• Episodic and sporadic abuse represents the most significant hazard identified through adverse event reporting, particularly when individuals intentionally ingest supratherapeutic doses seeking dissociative hallucinogenic effects 1, 5

Important Safety Notes

Dosing Considerations

• Standard over-the-counter dosing (typically 15-30 mg) is often subtherapeutic, with maximum cough suppression occurring at 60 mg 4, 2
• However, supratherapeutic doses mimic dissociative hallucinogens like phencyclidine and ketamine due to NMDA receptor antagonism 5

General Safety Profile

• When used appropriately, adverse drug reactions are infrequent and usually not severe, with predominant symptoms being dose-related neurological, cardiovascular, and gastrointestinal disturbances 1
• The safety profile is reassuring particularly regarding overdose in both adults and children when MAOI interaction is avoided 1