History

Fact Explanation
Drowsiness, fatigue, impairment of memory, somnolence [1] Due to central nervous system (CNS) toxicity. Antihistamine causes interference with neurotransmitter effect of histamine through H1 receptor and causes CNS depression [2]
Convulsions, confusion, agitation, a sensory experience of something that does not exist outside (hallucination) [1] Infants and children often exhibit initial paradoxical CNS stimulation, including agitation, hallucinations, confusion and convulsions before progressing to coma [2]
Palpitations [1] Due to cardiac toxicity. Antihistamine overdose can produce a variety of cardiac arrhythmias. For the majority of antihistamines this effect is mediated by myocardial sodium channel blockade—a quinidine like effect. Two of the newer non-sedating antihistamines, terfenadine and astemizole, cause delayed cardiac repolarization by potassium channel blockade. This is associated with prolongation of the QT interval and may predispose to the development of ventricular tachyarrhythmias [3]
Dry eyes , dry mouth, urinary retention, constipation, erectile dysfunction [1] Due to anticholinergic effects of anti histamine toxicity [2]
Nausea, vomiting [1] Due to anticholinergic effects of anti histamine toxicity [2]
Fever [1] Hyperthermia may occur due to impaired sweating (anticholinergic effect), increased production of heat (excessive motor activity, agitation and seizures) and central effects on thermoregulation [3]
Poor socio economic status [4] Toxicity due to over dose is high due to poor parental education, poor supervision of the parents [5]
References
  1. RIORDAN M. Poisoning in children 3: Common medicines. [online] 2002 November, 87(5):400-402 [viewed 06 August 2014] Available from: doi:10.1136/adc.87.5.400
  2. CHURCH M. K., MAURER M., SIMONS F. E. R., BINDSLEV-JENSEN C., VAN CAUWENBERGE P., BOUSQUET J., HOLGATE S. T., ZUBERBIER T.. Risk of first-generation H -antihistamines: a GA LEN position paper . [online] 2010 April, 65(4):459-466 [viewed 06 August 2014] Available from: doi:10.1111/j.1398-9995.2009.02325.x
  3. SIMONS F. ESTELLE R.. Advances in H -Antihistamines . N Engl J Med [online] 2004 November, 351(21):2203-2217 [viewed 06 August 2014] Available from: doi:10.1056/NEJMra033121
  4. JANG HS, KIM JY, CHOI SH, YOON YH, MOON SW, HONG YS, LEE SW. Comparative analysis of acute toxic poisoning in 2003 and 2011: analysis of 3 academic hospitals. J Korean Med Sci [online] 2013 Oct, 28(10):1424-30 [viewed 02 October 2014] Available from: doi:10.3346/jkms.2013.28.10.1424
  5. AHMED BILAL, FATMI ZAFAR, SIDDIQUI AMNA R., BHUTTA ZULFIQAR A.. Population Attributable Risk of Unintentional Childhood Poisoning in Karachi Pakistan. PLoS ONE [online] 2011 October [viewed 02 October 2014] Available from: doi:10.1371/journal.pone.0026881

Examination

Fact Explanation
Drowsiness [1] Due to central nervous system (CNS) toxicity. Antihistamine causes interference with neurotransmitter effect of histamine through H1 receptor and causes CNS depression.It can cause coma in severe toxicity [2]
Agitation, seizures [1] Infants and children often exhibit initial paradoxical CNS stimulation, including agitation, hallucinations, confusion and convulsions before progressing to coma [2]
Tachycardia [1] Due to cardiovascular system toxicity.Antihistamine overdose can produce a variety of cardiac arrhythmias. For the majority of antihistamines this effect is mediated by myocardial sodium channel blockade—a quinidine like effect. Two of the newer non-sedating antihistamines, terfenadine and astemizole, cause delayed cardiac repolarization by potassium channel blockade. This is associated with prolongation of the QT interval and may predispose to the development of ventricular tachyarrhythmias [3]
Dry eyes, dry mouth, pupillary dilatation [1] Due to anticholinergic effects of anti histamine toxicity [2]
Hypotension [1] Relative volume depletion and vasodilatation resulting from alpha receptor blockade [3]
Febrile [1] Hyperthermia may occur due to impaired sweating (anticholinergic effect), increased production of heat (excessive motor activity, agitation and seizures) and central effects on thermoregulation [3]
References
  1. RIORDAN M. Poisoning in children 3: Common medicines. [online] 2002 November, 87(5):400-402 [viewed 06 August 2014] Available from: doi:10.1136/adc.87.5.400
  2. CHURCH M. K., MAURER M., SIMONS F. E. R., BINDSLEV-JENSEN C., VAN CAUWENBERGE P., BOUSQUET J., HOLGATE S. T., ZUBERBIER T.. Risk of first-generation H -antihistamines: a GA LEN position paper . [online] 2010 April, 65(4):459-466 [viewed 06 August 2014] Available from: doi:10.1111/j.1398-9995.2009.02325.x
  3. SIMONS F. ESTELLE R.. Advances in H -Antihistamines . N Engl J Med [online] 2004 November, 351(21):2203-2217 [viewed 06 August 2014] Available from: doi:10.1056/NEJMra033121

Differential Diagnoses

Fact Explanation
Central nervous system infections [1] May present with drowsiness.Examination will be positive for specific signs ( eg: Kernig’s sign ) Lumbar puncture will help in the diagnosis [1]
Tricyclic antidepressant overdose [2] Will present with sedation and coma,seizures,hypotension and tachycardia.Electrocardiogram may have QT prolongation. Past history of a psychiatric illness may be positive [2]
References
  1. 1) CHáVEZ-BUENO SUSANA, MCCRACKEN GEORGE H.. Bacterial Meningitis in Children. Pediatric Clinics of North America [online] 2005 June, 52(3):795-810 [viewed 15 July 2014] Available from: doi:10.1016/j.pcl.2005.02.011
  2. KERR G W. Tricyclic antidepressant overdose: a review. [online] 2001 July, 18(4):236-241 [viewed 06 August 2014] Available from: doi:10.1136/emj.18.4.236

Investigations - for Diagnosis

Fact Explanation
Electrocardiogram [1] To identify arrhythmia. Antihistamine overdose can produce a variety of cardiac arrhythmias. For the majority of antihistamines this effect is mediated by myocardial sodium channel blockade—a quinidine like effect. Two of the newer non-sedating antihistamines, terfenadine and astemizole, cause delayed cardiac repolarization by potassium channel blockade. This is associated with prolongation of the QT interval and may predispose to the development of ventricular tachyarrhythmias [2]
Full blood count [1] Uncommonly, agranulocytosis has been reported with chlorpheniramine and brompheniramine [2]
References
  1. RIORDAN M. Poisoning in children 3: Common medicines. [online] 2002 November, 87(5):400-402 [viewed 06 August 2014] Available from: doi:10.1136/adc.87.5.400
  2. SIMONS F. ESTELLE R.. Advances in H -Antihistamines . N Engl J Med [online] 2004 November, 351(21):2203-2217 [viewed 06 August 2014] Available from: doi:10.1056/NEJMra033121

Investigations - Fitness for Management

Fact Explanation
Arterial blood gas analysis [1] All unconscious patients require arterial blood gas to access adequacy of ventilation and to ensure they are not acidotic [2]
References
  1. RIORDAN M. Poisoning in children 3: Common medicines. [online] 2002 November, 87(5):400-402 [viewed 06 August 2014] Available from: doi:10.1136/adc.87.5.400
  2. SIMONS F. ESTELLE R.. Advances in H -Antihistamines . N Engl J Med [online] 2004 November, 351(21):2203-2217 [viewed 06 August 2014] Available from: doi:10.1056/NEJMra033121

Investigations - Followup

Fact Explanation
Electrocardiogram [1] Patients with QT prolongation should be monitored until these changes resolve [2]
References
  1. RIORDAN M. Poisoning in children 3: Common medicines. [online] 2002 November, 87(5):400-402 [viewed 06 August 2014] Available from: doi:10.1136/adc.87.5.400
  2. SIMONS F. ESTELLE R.. Advances in H -Antihistamines . N Engl J Med [online] 2004 November, 351(21):2203-2217 [viewed 06 August 2014] Available from: doi:10.1056/NEJMra033121

Investigations - Screening/Staging

Fact Explanation
Electrocardiogram [1] This may be helpful in excluding other differentials (eg : normal ECG in central nervous system infections) [2]
Full blood count [1] To exclude central nervous system infections and other systemic infections which may present with drowsiness.Infections will show leukocytosis in full blood count [2]
creatine kinase level [1] This may be helpful if suspecting rhabdomyolysis secondary to antihistamine/decongestant combination which contains pseudoephedrine or phenylephrine [2]
References
  1. RIORDAN M. Poisoning in children 3: Common medicines. [online] 2002 November, 87(5):400-402 [viewed 06 August 2014] Available from: doi:10.1136/adc.87.5.400
  2. SIMONS F. ESTELLE R.. Advances in H -Antihistamines . N Engl J Med [online] 2004 November, 351(21):2203-2217 [viewed 06 August 2014] Available from: doi:10.1056/NEJMra033121

Management - General Measures

Fact Explanation
General emergency management - air way , breathing, circulation [1] All patients should have assessment of the adequacy of their airway protection and ventilation. Intravenous fluid may be required to maintain the circulation [1]
Parental education [3] , Community based programs [4] Parents should teach young children about the dangers of medicines. Advise the parents about the proper storage and labeling of medicines. Inform parents about common medications that may be dangerous. Educate parents that they need to supervise their children [2]
References
  1. RIORDAN M. Poisoning in children 3: Common medicines. [online] 2002 November, 87(5):400-402 [viewed 06 August 2014] Available from: doi:10.1136/adc.87.5.400
  2. SIBERT J R, ROUTLEDGE P A. Accidental poisoning in children: can we admit fewer children with safety?. Archives of Disease in Childhood [online] 1991 February, 66(2):263-266 [viewed 06 August 2014] Available from: doi:10.1136/adc.66.2.263
  3. KING W. J., KLASSEN T. P., LEBLANC J., BERNARD-BONNIN A.-C., ROBITAILLE Y., PHAM B., COYLE D., TENENBEIN M., PLESS I. B.. The Effectiveness of a Home Visit to Prevent Childhood Injury. PEDIATRICS [online] 2001 August, 108(2):382-388 [viewed 02 October 2014] Available from: doi:10.1542/peds.108.2.382
  4. NIXON J. Community based programs to prevent poisoning in children 0-15 years. Injury Prevention [online] 2004 January, 10(1):43-46 [viewed 02 October 2014] Available from: doi:10.1136/ip.2003.003822

Management - Specific Treatments

Fact Explanation
Gastrointestinal decontamination [1] Activated charcoal should be considered up to four hours post-ingestion [1]
Intra venous fluid [1] For the treatment of hypotension [1]
Benzodiazepine ( Diazepam ) [1] Convulsions and paradoxical excitement can be treated with a benzodiazepine [1]
Sodium bicarbonate [1] Sodium bicarbonate is the first drug of choice for QT prolongation with sodium channel blocking antihistamines [1]
References
  1. RIORDAN M. Poisoning in children 3: Common medicines. [online] 2002 November, 87(5):400-402 [viewed 06 August 2014] Available from: doi:10.1136/adc.87.5.400