What are the immediate treatment steps for a patient who collapsed after ingesting 5mL of a dose of Dextromethorphan (cough suppressant), Phenylephrine (decongestant) and Chlorpheniramine (antihistamine) maleate?

Immediate Management of Collapse After Cough/Cold Medication Ingestion

Activate emergency medical services immediately and initiate standard Basic Life Support (BLS) and Advanced Cardiovascular Life Support (ACLS) protocols, as these take absolute priority over any antidote or specific treatment considerations. 1

Initial Resuscitation (First 5 Minutes)

Airway and Breathing Assessment

• Establish airway patency and assess breathing immediately - if the patient has no normal breathing or only gasping with a definite pulse present, provide rescue breathing or bag-mask ventilation 1
• Position the patient supine and open the airway using standard maneuvers 1
• If respiratory arrest is present without cardiac arrest, maintain rescue breathing until spontaneous breathing returns 1

Circulation and Cardiac Assessment

• Check for pulse and signs of circulation - if cardiac arrest is confirmed (no pulse, no breathing), immediately begin high-quality CPR with compressions and ventilation 1
• Obtain vital signs as soon as possible, but do not delay treatment if the reaction appears severe 1
• Place patient in recumbent position with elevated lower extremities if hypotension is present 1

Differential Diagnosis Considerations

Anaphylaxis (Most Life-Threatening Possibility)

If there are any signs of systemic allergic reaction—especially hypotension, airway swelling, difficulty breathing, or skin/mucosal involvement—administer intramuscular epinephrine 0.3-0.5 mg (1:1000 concentration) into the vastus lateralis immediately. 1, 2

• Anaphylaxis can occur to any component: dextromethorphan, phenylephrine, or chlorpheniramine 1
• Epinephrine has no absolute contraindications in anaphylaxis - delayed administration is associated with fatalities 1, 2
• Repeat epinephrine every 5-15 minutes as needed if inadequate response 1, 2
• Administer rapid IV fluid bolus of 500-1000 mL crystalloid for hypotension 1

Drug Toxicity/CNS Depression

• The combination of dextromethorphan and chlorpheniramine can cause profound CNS depression, particularly at supratherapeutic doses 3, 4
• Blood dextromethorphan concentrations >150 ng/mL with chlorpheniramine >70 ng/mL have been associated with severe CNS depression and impairment 3
• However, 5mL of standard formulation is typically a therapeutic dose - collapse from this amount suggests either anaphylaxis, underlying metabolic abnormality, or drug interaction 5, 6

Critical Drug Interaction Warning

• Approximately 5% of individuals of European ancestry are CYP2D6 poor metabolizers who cannot metabolize dextromethorphan normally, leading to rapid toxic accumulation 5, 6
• If the patient is taking tricyclic antidepressants, SSRIs, or other CYP2D6 inhibitors, even therapeutic dextromethorphan doses can cause life-threatening toxicity including coma and serotonin syndrome 6, 4

Ongoing Management

If Anaphylaxis is Confirmed

• Continue epinephrine 0.3-0.5 mg IM every 5-15 minutes until symptoms resolve 1, 2
• Aggressive fluid resuscitation with crystalloid boluses 1
• After stabilization with epinephrine and fluids, IV antihistamines (diphenhydramine or chlorpheniramine) may be administered, but are not a priority 1
• Do not administer IV promethazine - it is not appropriate for anaphylaxis management 1
• Observe in monitored setting for minimum 6 hours after symptom resolution due to risk of biphasic reaction 1

If Cardiac Arrest Occurs

• Follow standard ACLS guidelines with IV/IO epinephrine 1 mg every 3-5 minutes 1, 2
• High-quality CPR takes absolute priority over any antidote considerations 1
• Standard resuscitative measures should not be delayed for naloxone or other specific antidotes 1

Supportive Care for Drug Toxicity

• Maintain airway protection - consider endotracheal intubation if unable to protect airway 1
• Provide supplemental oxygen for hypoxia 1
• IV fluid resuscitation for hypotension 1
• Contact Poison Control Center (1-800-222-1222 in US) for specific guidance 1, 7

Critical Pitfalls to Avoid

• Never delay epinephrine administration in suspected anaphylaxis - approximately 200 Americans die annually from anaphylaxis, mostly from medication reactions, and delayed epinephrine is the primary cause of preventable deaths 1, 2
• Do not assume a "therapeutic dose" is safe - individual variation in drug metabolism can cause severe toxicity even at standard doses 5, 6
• Do not use antihistamines or corticosteroids as first-line treatment for anaphylaxis - only epinephrine addresses life-threatening manifestations 1
• Approximately 10-20% of anaphylaxis patients require more than one dose of epinephrine 2