About Anaphylaxis

• Triggers
• Risk factors
• Mechanisms
• Epidemiology
• Symptoms
• Diagnosis
• When to refer

Further information:

Prescribing Information

Patient Information Leaflet

Risk factors

Anaphylaxis often occurs more than once and subsequent reactions may be more severe than the first reaction. In a retrospective analysis of 266 subjects, 76% of subjects who experienced anaphylaxis had another anaphylactic reaction.¹² Furthermore, fatal allergen-induced anaphylaxis occurred in 22% of patients who had a previous severe reaction to food, and 18% of patients who had a previous severe reaction to venom. ¹³

In addition to a history of anaphylaxis, other factors that may increase the risk of experiencing a severe or fatal episode are:¹⁴

• Comorbidities: people who have allergies or asthma are at increased risk of having anaphylaxis, especially if poorly controlled.
  
  Other comorbidities that increase the risk include hypertension, depression (may impair recognition of symptoms), thyroid disease and underlying cardiac condition.
  
  Defects in mediator degradation pathways may result in elevated baseline levels of tryptase, histamine, bradykinin or platelet activating factor and contribute to severity of anaphylactic episodes.¹⁵
  
  Information on co-morbidities in patients with anaphylaxis can also be found in Precautions and Contraindications and Interactions.
  

• Age: anaphylaxis in infants can be underdiagnosed because they are unable to describe their symptoms, added to which symptoms may be similar to those normally encountered in a healthy infant (such as flushing, loose stools).

  Risk-taking behaviour in adolescents and young adults i.e. failure to avoid triggers.

  Antibiotic prophylaxis in pregnancy is a common trigger.

  Risk of fatality from medication and venom-triggered anaphylaxis is increased in the elderly. This age group is also at increased risk of anaphylaxis as a result of concomitant diseases.

• Co-medication: some medications can affect the recognition of anaphylaxis (psychotropic agents or recreational drugs) while others can increase severity (e.g. beta-blockers and ACE inhibitors).

Information on co-medication in patients with anaphylaxis can also be found in Precautions and Interactions.

• A family history: people with family members who have experienced exercised-induced anaphylaxis, have a higher risk of developing this type of anaphylaxis than someone without a family history.¹⁶

There are also a number of co-factors that amplify anaphylaxis, including exercise, acute infection (e.g. colds, fever), emotional stress, disruption of routine (e.g. travel) and pre-menstrual status.