What are the consequences of a chlorpheniramine overdose in a 4-year-old boy who received a wrong dose of 5mg?

Consequences of Chlorpheniramine Overdose in a 4-Year-Old Child

A 5mg dose of chlorpheniramine in a 4-year-old child is a significant overdose that requires immediate medical attention due to potential central nervous system and cardiovascular effects.

Appropriate Dosing vs. Given Dose

According to the FDA drug label, chlorpheniramine is not recommended for children under 6 years of age 1. For children 6-12 years, the recommended dose is only 2.5mg (half a tablet) every 4-6 hours, not exceeding 3 tablets in 24 hours 2.

The 5mg dose administered to a 4-year-old represents approximately double the dose that would be given to an older child (6-12 years), and is completely contraindicated for this age group.

Potential Consequences of Overdose

Central Nervous System Effects

• Sedation and drowsiness (most common)
• Paradoxical excitation or agitation
• Confusion and altered mental status
• Seizures in severe cases
• Reduced cognitive function and impaired coordination
• Potential for coma in significant overdose

Cardiovascular Effects

• Tachycardia (increased heart rate)
• Potential for QT interval prolongation and arrhythmias
• Hypertension or hypotension

Anticholinergic Effects

• Dry mouth and eyes
• Flushing
• Hyperthermia (fever)
• Urinary retention
• Constipation

Severity Assessment

The severity of symptoms depends on:

• The child's weight (5mg represents a higher mg/kg dose in a smaller child)
• Individual sensitivity to antihistamines
• Time since ingestion
• Whether other medications were co-administered

Management Approach

1. Immediate Assessment:

   • Evaluate vital signs (heart rate, blood pressure, respiratory rate, temperature)
   • Assess level of consciousness using age-appropriate methods
   • Monitor for seizures or cardiac abnormalities

2. Supportive Care:

   • Ensure airway, breathing, and circulation are maintained
   • Consider activated charcoal if within 1 hour of ingestion and the child is alert
   • IV access for medication administration if needed

3. Specific Monitoring:

   • Cardiac monitoring for at least 4-6 hours
   • Observation for at least 6 hours after ingestion
   • Extended monitoring if symptoms are present

Case Reports of Chlorpheniramine Toxicity

Several case reports highlight the potential dangers:

• A 13-month-old child developed convulsions, coma, tachycardia, and fever after ingestion of a product containing chlorpheniramine 3
• Rhabdomyolysis (muscle breakdown) has been reported in severe chlorpheniramine overdose 4
• CNS effects including impaired attention and visuo-motor coordination may occur even without subjective awareness of impairment 5

Common Pitfalls to Avoid

1. Underestimating toxicity: First-generation antihistamines like chlorpheniramine have significant CNS effects compared to newer antihistamines.

2. Premature discharge: Effects may be delayed or prolonged due to the drug's pharmacokinetics.

3. Missing co-ingestions: Consider whether other medications might have been administered simultaneously.

4. Inadequate monitoring: Cardiac and neurological monitoring are essential even if initial symptoms appear mild.

When to Seek Emergency Care

Immediate medical attention is warranted if the child shows:

• Altered mental status or extreme sedation
• Seizures
• Irregular heartbeat or significant tachycardia
• Fever
• Inability to urinate
• Agitation or hallucinations

The American Academy of Pediatrics has highlighted concerns about the safety of cough and cold medications (including antihistamines like chlorpheniramine) in young children, noting that they have been associated with fatalities in pediatric patients 2, 6.