Chlorpheniramine 30mg + Phenylephrine 37.5mg Overdose in a 12 kg Child - Management & Complications

Dose Assessment First

• Chlorpheniramine: ~0.1 mg/kg/dose → normal dose ≈ 1.2 mg; this child received 30 mg = ~2.5 mg/kg (approximately 25x the therapeutic dose)
• Phenylephrine: ~0.1 mg/kg/dose → normal dose ≈ 1.2 mg; this child received 37.5 mg = ~3.1 mg/kg (approximately 30x the therapeutic dose)

Mechanism of Toxicity

• At overdose levels, causes a classic anticholinergic toxidrome (dry hot skin, tachycardia, mydriasis, urinary retention, ileus, altered sensorium, seizures)
• Also has significant CNS effects - may cause paradoxical CNS stimulation in children (excitation, agitation, seizures) before sedation sets in
• Toxic dose in children is considered >1.5-2 mg/kg - this child has ingested ~2.5 mg/kg

• At overdose levels, causes a sympathomimetic/adrenergic toxidrome: hypertension (potentially severe due to peripheral vasoconstriction), reflex bradycardia (via baroreceptor response to hypertension), headache, anxiety, arrhythmias, seizures
• Toxic dose is generally >1 mg/kg - this child has ingested ~3.1 mg/kg

Immediate Management

Step 1 - Stabilize and Monitor

• Establish IV access immediately
• Continuous cardiac monitoring (pulse oximetry, ECG, respiratory rate, BP)
• Check blood glucose
• Baseline vitals every 15-30 minutes for at least the first 4-6 hours
• The child is currently asymptomatic but is still within the absorption window - symptoms may appear at 1-4 hours post-ingestion

Step 2 - Gastrointestinal Decontamination

• Activated charcoal (AC) 1 g/kg (max 50g) orally/NG if:
  • Presentation is within 1-2 hours of ingestion (this child is at 30 minutes - still eligible)
  • Airway is protected (child is alert and cooperative)
  • No contraindications (altered sensorium, vomiting, unprotected airway)
• Given the child is hemodynamically stable and alert at 30 minutes, AC should be strongly considered and given as soon as possible
• Gastric lavage is generally not recommended unless a massive dose was ingested and the child presents within 1 hour with airway protection - may be considered here but AC is preferred
• Do NOT induce emesis (risk of rapid CNS depression, seizures)

Step 3 - Observation Period

• Minimum 6-8 hours of observation in a monitored setting after last vital signs are stable
• Because phenylephrine can cause delayed cardiovascular effects and chlorpheniramine can cause delayed CNS effects, early discharge is not appropriate
• If symptomatic, admit to a PICU/pediatric high-dependency unit

Step 4 - Contact Poison Control

• Contact regional Poison Control Center (e.g., India Poison Control: 1800-116-117) for real-time guidance

Potential Complications to Monitor For

1. Seizures - most feared with chlorpheniramine overdose in children; may be sudden in onset
2. Severe hypertension - from phenylephrine alpha-1 agonism; can cause hypertensive encephalopathy
3. Reflex bradycardia - severe vasoconstriction from phenylephrine triggers baroreceptor reflex
4. Arrhythmias - tachycardia from anticholinergic + bradycardia from phenylephrine = unpredictable rhythm
5. Hyperthermia - anticholinergic impairs sweating + sympathomimetic increases metabolic rate
6. CNS depression/coma - high chlorpheniramine dose can progress to coma after initial excitation
7. Rhabdomyolysis - reported with chlorpheniramine poisoning; monitor CK and renal function

Specific Treatment for Complications

Disposition

Key Points to Remember

1. Asymptomatic at 30 minutes does NOT mean safe - the child is still in the absorption phase. Most symptoms with these drugs appear within 1-4 hours.
2. Chlorpheniramine 30mg in a 12kg child = ~2.5 mg/kg - this is a definite toxic dose.
3. Activated charcoal at 30 minutes is appropriate and should be given now if the airway is protected.
4. Do not use flumazenil or other CNS reversal agents inappropriately.
5. Avoid atropine for bradycardia if caused by phenylephrine reflex (it will worsen paradoxically).
6. The combination of anticholinergic and sympathomimetic drugs creates competing effects - expect unpredictability.

Always contact your regional Poison Control Center for real-time dosing guidance and case-by-case advice in pediatric toxicology emergencies.