From the Guidelines
Chlorpheniramine overdose is a medical emergency that requires immediate attention, and if suspected, one should call poison control or go to the emergency room immediately. The symptoms of an overdose can be severe and include extreme drowsiness, confusion, hallucinations, dilated pupils, dry mouth, flushing, fever, rapid heartbeat, seizures, and in severe cases, respiratory depression, coma, or death 1. Treatment typically involves supportive care, possibly including activated charcoal if the ingestion was recent, monitoring of vital signs, IV fluids, and management of specific symptoms.
Key Considerations
- Children, especially those under 6 years of age, are at a higher risk for severe reactions due to the potential toxicity of antihistamines like chlorpheniramine, as evidenced by reports of fatalities associated with its use in young children 1.
- The elderly are also at a higher risk for severe reactions.
- Chlorpheniramine is an antihistamine commonly found in allergy and cold medications, with a typical therapeutic dose of 4mg every 4-6 hours (not exceeding 24mg daily for adults).
Management and Prevention
- Overdose occurs when the therapeutic amount is significantly exceeded, either accidentally or intentionally.
- The medication works by blocking histamine receptors but in excess can affect multiple body systems, particularly the central nervous system and cardiovascular system, explaining the wide range of overdose symptoms.
- Given the concerns over safety, especially in children, it is crucial to follow dosing recommendations carefully and to be aware of the potential for overdose and toxicity when using chlorpheniramine or any other medication containing antihistamines 1.
From the Research
Chlorpheniramine Overdose
- Chlorpheniramine is an antihistamine that can cause anticholinergic toxicity in overdose, characterized by symptoms such as mydriasis, blurred vision, tremors, ataxia, fever, flushed and dry skin, dry oral mucosa, decreased bowel sounds, constipation, and urinary retention 2.
- In extreme cases, anticholinergic toxicity can lead to seizures, coma, respiratory failure, and cardiovascular collapse 3, 4, 5.
- Physostigmine, a cholinesterase inhibitor, can be used to treat anticholinergic toxicity, including that caused by chlorpheniramine overdose 3, 4, 5.
- A case report describes a fatal intoxication with guaifenesin, diphenhydramine, and chlorpheniramine, highlighting the potential dangers of mixed drug reactions 2.
- Chlorpheniramine has also been shown to have selective serotonin-reuptake inhibitor (SSRI) effects, and may be useful in the treatment of depression and panic disorder 6.
Treatment of Chlorpheniramine Overdose
- Treatment of chlorpheniramine overdose typically involves supportive care, including cardiac, neurological, and respiratory monitoring 3, 4, 5.
- Physostigmine may be used to reverse anticholinergic delirium and other symptoms of overdose, although its use is not without risk and should be carefully considered 3, 4, 5.
- Continuous infusion of physostigmine has been used successfully in some cases to reverse anticholinergic delirium, but its use is rare due to concerns about cardiotoxicity and cholinergic excess 5.