Acute Allergic Reaction (Anaphylaxis)


An acute allergic reaction or anaphylaxis is a life-threatening but rapidly reversible condition if treated promptly.

Anaphylaxis can develop within minutes of injection or ingestion of medicines or contact with allergen.

Persons who are aware of the risk of anaphylaxis are to be informed of avoidance measures, and may be taught the use of an epinephrine (adrenaline) pen.

Causes of acute allergic reaction or anaphylaxis

  1. Bee or other insect stings
  2. Drugs e.g. penicillins, sulphonamides
  3. Vaccines
  4. Antisera e.g. snake serum, anti-tetanus serum
  5. Intravenous contrast media
  6. Foods like seafood, groundnuts, fruit etc.

Symptoms of acute allergic reaction or anaphylaxis

  1. Severe itching
  2. Urticarial rash
  3. Facial and peri-oral swelling
  4. Difficulty in breathing
  5. Wheeze
  6. Collapse
  7. Syncope

Signs of acute allergic reaction or anaphylaxis

  • Angio-oedema
  • Difficulty in breathing
  • Bronchospasm with wheeze
  • Tachycardia
  • Hypotension
  • Cold clammy extremities
  • Facial oedema
  • Urticaria
  • Cyanosis


  • FBC (eosinophilia)
  • Skin prick test for specific allergens
  • Serum specific IgE

Treatment for acute allergic reaction or anaphylaxis


  1. Secure airways, breathing and circulation
  2. Reverse symptoms
  3. Remove the offending cause if possible
  4. Rapidly intervene and correct abnormal vital signs

Non-pharmacological treatment

  • Avoid the allergen
  • Resuscitation

Pharmacological treatment

A. Acute Anaphylactic Reaction

1st Line Treatment

Evidence Rating: [B]


By nasal prongs 2-6 L/min


Face mask 4-8 L/min


Non-rebreather mask, 10-15 L/min


Adrenaline (Epinephrine), IM,

Adults: 0.3-0.5 ml of 1:1000 solution
(i.e. 300-500 micrograms) repeated if necessary every 10 minutes and while monitoring blood pressure and pulse


0.3 ml of 1:1000 solution (i.e. 300 micrograms). Repeat as for adults.


Hydrocortisone, IV,


100-200 mg 6-8 hourly, to control any late allergic reaction that may occur


All ages; 250 mg/day


Prednisolone, oral,


2 mg/kg 6 hourly for 4 doses, not to exceed 40 mg daily for 14 days and taper off


2 mg/kg daily for 14 days and taper off


Promethazine hydrochloride, IM,


25 mg repeat after 2 hours if necessary,
Then 12 hourly for 24 hours


  • 2 years-12 years; 6.25-12.5 mg 8-12 hourly for 24 hours
  • < 2 years; Not recommended


Chlorpheniramine, IM,

Adults 5-10 mg 6 hourly (max. of 40 mg daily)


  • 6-12 years; 5mg up to a max. of 4 doses in 24 hours
  • 6 months-6 years; 2.5 mg,
  • < 6 month; 250 microgram/kg (max. 1.5 mg)

B. Acute Anaphylactic Reaction with severe airway obstruction)

Above plan


Salbutamol, nebulised,

Adults: 5 mg 4-6 hourly until resolved

Children: 2.5 mg 4-6 hourly until resolved


Aminophylline, IV,


250 mg over 20 minutes, then continuous infusion by perfusor at 0.5 mg/kg/hour for 24 hours if necessary


3-5 mg/kg over 20 minutes as a slow bolus injection or by infusion in 500 ml Sodium Chloride 0.9%, IV, 4-6 hourly for 24 hours

C. Acute Anaphylactic Reaction with severe hypotension

Above plan


Normal saline, 0.9%, IV, 1 L – 4 L, rate determined by clinical assessment

Referral Criteria

Refer to district or regional hospital if symptoms of anaphylaxis persist after stabilizing the patient and giving initial treatment.

Leave a Comment