Poisoning - Antihistamines - Clinicals, Diagnosis, and Management

Emergency Medicine

Clinicals - History

Fact Explanation
Drowsiness Occurs due to brain H1-receptor blockage. This is the most common presentation Drowsiness
Occurs due to brain H1-receptor blockage. This is the most common presentation
Dizziness Is a presentation due to brain H1-receptor blockage Dizziness
Is a presentation due to brain H1-receptor blockage
Somnolence Occurs due to brain H1-receptor blockage Somnolence
Occurs due to brain H1-receptor blockage
Inability to concentrate Occurs also due to brain H1-receptor blockage Inability to concentrate
Occurs also due to brain H1-receptor blockage
Agitation Occurs due to brain H1-receptor blockage and /or anticholinergic/antimuscarinic effect seen in some antihistamine drugs Agitation
Occurs due to brain H1-receptor blockage and /or anticholinergic/antimuscarinic effect seen in some antihistamine drugs
Incoordination Is a presentation in some patients with antihistamine poisoning Incoordination
Is a presentation in some patients with antihistamine poisoning
Dry mouth Occurs due to the anticholinergic/antimuscarinic effect of antihistamines Dry mouth
Occurs due to the anticholinergic/antimuscarinic effect of antihistamines
Blurred vision Occurs due to the anticholinergic/antimuscarinic effect Blurred vision
Occurs due to the anticholinergic/antimuscarinic effect
Difficulty passing urine Occurs due to the peripheral anticholinergic/antimuscarinic effect Difficulty passing urine
Occurs due to the peripheral anticholinergic/antimuscarinic effect
Nervousness Occurs also due to brain H1-receptor blockage Nervousness
Occurs also due to brain H1-receptor blockage
Hallucinations Is present in some patients with antihistamine poisoning. These occur mainly due to anticholinergic actions at muscarinic receptors Hallucinations
Is present in some patients with antihistamine poisoning. These occur mainly due to anticholinergic actions at muscarinic receptors
Insomnia Somnolence caused by first generation antihistamines interfere with the natural circadian sleep-wake cycle leading to insomnia in some patients Insomnia
Somnolence caused by first generation antihistamines interfere with the natural circadian sleep-wake cycle leading to insomnia in some patients
Tremor Is present in some patients. This occurs due to antimuscarinic effect on the central nervous system of some antihistamines Tremor
Is present in some patients. This occurs due to antimuscarinic effect on the central nervous system of some antihistamines
Convulsions/seizures Occurs also due to brain H1-receptor blockage and anticholinergic actions at muscarinic receptors Convulsions/seizures
Occurs also due to brain H1-receptor blockage and anticholinergic actions at muscarinic receptors
Constipation Occurs due to the anticholinergic/antimuscarinic effect seen in some antihistamine drugs, but some patients may develop diarrhea Constipation
Occurs due to the anticholinergic/antimuscarinic effect seen in some antihistamine drugs, but some patients may develop diarrhea
Difficulty swallowing Occurs due to antimuscarinic blockage Difficulty swallowing
Occurs due to antimuscarinic blockage
Difficulty breathing Respiratory depression is seen in severe antihistamine poisoning Difficulty breathing
Respiratory depression is seen in severe antihistamine poisoning
Dystonic reactions These are extrapyramidal side effects that result due to antidopaminergic action of some antihistamines. These include oculogyric crisis (i.e.deviation of eyes in all directions), involuntary protrusion of tongue,trismus, difficulty in speaking, facial grimacing, torticollis etc. that result from involuntary contraction of muscles Dystonic reactions
These are extrapyramidal side effects that result due to antidopaminergic action of some antihistamines. These include oculogyric crisis (i.e.deviation of eyes in all directions), involuntary protrusion of tongue,trismus, difficulty in speaking, facial grimacing, torticollis etc. that result from involuntary contraction of muscles

Clinicals - Examination

Fact Explanation
Dilated pupil Is due to the anticholinergic effect Dilated pupil
Is due to the anticholinergic effect
Tachycardia Occurs due to the anticholinergic/antimuscarinic effect seen in some antihistamine drugs Tachycardia
Occurs due to the anticholinergic/antimuscarinic effect seen in some antihistamine drugs
Muscle weakness Is seen in some with patients antihistamine toxicity and may indicate presence of rhabdomyolysis, in which case patient may have additional symptoms such as myalgia and dark color urine Muscle weakness
Is seen in some with patients antihistamine toxicity and may indicate presence of rhabdomyolysis, in which case patient may have additional symptoms such as myalgia and dark color urine
Incoordination Have been reported in some instances, secondary to anticholinergic actions at muscarinic receptors Incoordination
Have been reported in some instances, secondary to anticholinergic actions at muscarinic receptors
Increased body temperature (hyperpyrexia) Is seen in patients with antihistamine poisoning Increased body temperature (hyperpyrexia)
Is seen in patients with antihistamine poisoning
Reduced respiratory rate Respiratory depression is seen in some patients with antihistamine poisoning Reduced respiratory rate
Respiratory depression is seen in some patients with antihistamine poisoning
Arrythmia Occurs due to blockage of fast sodium channels. Arrhythmia may also arise secondary to anticholinergic actions at muscarinic receptors Arrythmia
Occurs due to blockage of fast sodium channels. Arrhythmia may also arise secondary to anticholinergic actions at muscarinic receptors
Flushed skin Is seen in some patients with antihitamine poisoning Flushed skin
Is seen in some patients with antihitamine poisoning
Reduced bowel sounds Occurs mainly due to anticholinergic actions at muscarinic receptors Reduced bowel sounds
Occurs mainly due to anticholinergic actions at muscarinic receptors
Changes in blood pressure Hypertension or hypotension can result from cardiac toxicity caused in antihistamine overdose Changes in blood pressure
Hypertension or hypotension can result from cardiac toxicity caused in antihistamine overdose

Investigations - Diagnosis

Fact Explanation
Toxicology screen for antihistamines Samples of blood and urine can be tested for presence of antihistamines Toxicology screen for antihistamines
Samples of blood and urine can be tested for presence of antihistamines

Investigations - Management

Fact Explanation
Complete blood count Done to detect leucopenia and agranulocytosis, that can occur rarely Complete blood count
Done to detect leucopenia and agranulocytosis, that can occur rarely
Blood culture Done to exclude systemic infections in patients presenting with pyrexia, delirium etc. Blood culture
Done to exclude systemic infections in patients presenting with pyrexia, delirium etc.
Serum electrolytes Should be done in patients with cardiac toxicity or delirium to exclude the presence of electrolyte imbalance Serum electrolytes
Should be done in patients with cardiac toxicity or delirium to exclude the presence of electrolyte imbalance
Serum creatinine kinase level Done to rule our rhabdomyolysis, as some patients with antihistamine toxicity may develop rhabdomyolysis Serum creatinine kinase level
Done to rule our rhabdomyolysis, as some patients with antihistamine toxicity may develop rhabdomyolysis
Electrocardiogram(ECG) It is important to take a 12-lead ECG to detect arrhythmia that can result from antihistamine toxicity Electrocardiogram(ECG)
It is important to take a 12-lead ECG to detect arrhythmia that can result from antihistamine toxicity
Liver function tests Done because some antihistamines can cause hepatotoxicity Liver function tests
Done because some antihistamines can cause hepatotoxicity

Management - Supportive

Fact Explanation
Emergency management Assess and secure the airway, breathing and circulation in any patient in an acute debilitated state. Once there is no acute threat to life take a relevant brief history and do relevant examination to recognize the potential cause for the patient's presentation Emergency management
Assess and secure the airway, breathing and circulation in any patient in an acute debilitated state. Once there is no acute threat to life take a relevant brief history and do relevant examination to recognize the potential cause for the patient's presentation
Oxygen therapy and assissted ventilation Is given to patients with impaired respiration Oxygen therapy and assissted ventilation
Is given to patients with impaired respiration
Physostigmine This drug is given via intravenous route to patients presenting with severe agitated delirium, to calm the patient Physostigmine
This drug is given via intravenous route to patients presenting with severe agitated delirium, to calm the patient
Management of seizures Benzodiazepines such as diazepam is given via intravenous route if patient develops seizures in order to control seizures Management of seizures
Benzodiazepines such as diazepam is given via intravenous route if patient develops seizures in order to control seizures
Sodium bicarbonte Is given via intravenous route to manage the cardiac toxicity caused by antihistamine poisoning, if ECG shows QRS complex widening Sodium bicarbonte
Is given via intravenous route to manage the cardiac toxicity caused by antihistamine poisoning, if ECG shows QRS complex widening
Temporary cardiac pacing Should be tried in patients developing atrio-ventricular block following severe toxicity Temporary cardiac pacing
Should be tried in patients developing atrio-ventricular block following severe toxicity
Magnesium sulphate Can be given to control torsades de pointes type of ventricular arrythmia if patient develops them Magnesium sulphate
Can be given to control torsades de pointes type of ventricular arrythmia if patient develops them
Psychiatric referral Should be done if the patient committed deliberate self harm/had suicide intent or if he/she is a known patient with a psychiatric disorder Psychiatric referral
Should be done if the patient committed deliberate self harm/had suicide intent or if he/she is a known patient with a psychiatric disorder
Management of rhabdomyolysis The aim of treatment is to prevent myoglobinuric acute kidney injury which occurs because of renal vasoconstriction and myoglobin precipitation resulting in renal tubule obstruction and injury. This is augmented by intravascular volume depletion that results from sequestration of fluid in damaged myocytes. The treatment for rhabdomyolysis is aggressive intravenous hydration to correct the intravascular volume depletion and renal vasoconstriction Management of rhabdomyolysis
The aim of treatment is to prevent myoglobinuric acute kidney injury which occurs because of renal vasoconstriction and myoglobin precipitation resulting in renal tubule obstruction and injury. This is augmented by intravascular volume depletion that results from sequestration of fluid in damaged myocytes. The treatment for rhabdomyolysis is aggressive intravenous hydration to correct the intravascular volume depletion and renal vasoconstriction
Management of dystonic reactions To manage dystonic reactions, oxygen is given by face mask and an anticholinergic agent such as intramuscular biperiden lactate 1 mg stat should be given Management of dystonic reactions
To manage dystonic reactions, oxygen is given by face mask and an anticholinergic agent such as intramuscular biperiden lactate 1 mg stat should be given
Management of hyperthermia Controlling hypothermia is done by removal of all unnecessary clothing, placing patient under a fan (place with increased air circulation), tepid sponging etc. If the patient is severely agitated and has a very high temperature may even require neuromuscular paralysis to control hyperthermia Management of hyperthermia
Controlling hypothermia is done by removal of all unnecessary clothing, placing patient under a fan (place with increased air circulation), tepid sponging etc. If the patient is severely agitated and has a very high temperature may even require neuromuscular paralysis to control hyperthermia

Management - Specific

Fact Explanation
Activated charcoal Activate charcoal 50-100 g in 200 mL of water is given orally. This reduces absorption of the ingested antihistamines in to the circulation through the gut Activated charcoal
Activate charcoal 50-100 g in 200 mL of water is given orally. This reduces absorption of the ingested antihistamines in to the circulation through the gut
Gastric aspiration and lavage Is not routinely done for all patients. Useful if only done within 1-2 hours from a life threatening ingestion. Done in the presence of a doctor and in a patient with a protected airway.Should not be done if the patient develops seizures, uncooperative or clinically unstable Gastric aspiration and lavage
Is not routinely done for all patients. Useful if only done within 1-2 hours from a life threatening ingestion. Done in the presence of a doctor and in a patient with a protected airway.Should not be done if the patient develops seizures, uncooperative or clinically unstable

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