What is anaphylaxis?
Anaphylaxis is a severe, life-threatening, systemic hypersensitivity reaction. It usually starts within minutes of exposure and can kill through airway swelling, severe bronchospasm or circulatory collapse. It can happen anywhere: a ward, a vaccination clinic, a pharmacy, a physiotherapy gym, a patient's home or the street.
Triggers differ by setting. In hospital, medicines are a leading cause, especially antibiotics, neuromuscular blocking drugs, chlorhexidine and contrast media. In the community, foods (peanuts, tree nuts, milk, egg, shellfish) and insect stings are common, particularly in children and young people. Sometimes no trigger is found.
How do you recognise anaphylaxis?
Resuscitation Council UK describes anaphylaxis as likely when there is sudden onset and rapid progression of symptoms, with life-threatening problems of the airway, breathing or circulation. Skin or mucosal changes are common but can be absent, subtle or late. Do not wait for a rash.
| System | Features to look for |
|---|---|
| Airway | Throat or tongue swelling, difficulty breathing or swallowing, hoarse voice, stridor, a feeling the throat is closing |
| Breathing | Breathlessness, fast breathing, wheeze, tiredness, confusion from hypoxia, cyanosis (late) |
| Circulation | Pale clammy skin, tachycardia, hypotension, feeling faint, reduced consciousness, cardiac arrest |
| Skin and mucosa | Hives, flushing, itching, swelling of lips, eyelids or face (often present, not required) |
| Other | Abdominal pain, vomiting, diarrhoea, a sense of impending doom |
What is not anaphylaxis?
Skin features alone, such as hives or mild lip swelling with no airway, breathing or circulation problem, are not anaphylaxis, although the patient should be observed because some reactions progress. A faint after an injection usually causes a slow pulse, pallor and quick recovery when lying flat, without wheeze or swelling. A panic attack may cause breathlessness and tingling but not hypotension, wheeze or hives. If you are unsure, treat it as anaphylaxis. An unnecessary IM dose carries far less risk than withholding one.
Tomasz, 46, is five minutes into his first IV dose of co-amoxiclav when he says he feels strange and dizzy. His blood pressure has dropped from 128/80 to 82/50 and his pulse is 124. There is no rash. Sudden, rapidly progressing circulatory compromise after a likely trigger means anaphylaxis is likely. The nurse stops the infusion, calls for help, lays him flat with legs raised and gives IM adrenaline.
What are the adrenaline doses for anaphylaxis in the UK?
Resuscitation Council UK sets out intramuscular doses of 1 mg/mL (1:1,000) adrenaline by age. Give it into the anterolateral aspect of the middle third of the thigh. Always check the current Resuscitation Council UK guidance and your local emergency protocol.
| Age | IM adrenaline dose | Volume of 1 mg/mL (1:1,000) |
|---|---|---|
| Adults and children over 12 years | 500 micrograms | 0.5 mL |
| Children over 12 who are small or prepubertal | 300 micrograms | 0.3 mL |
| Children 6 to 12 years | 300 micrograms | 0.3 mL |
| Children 6 months to 6 years | 150 micrograms | 0.15 mL |
| Children under 6 months | 100 to 150 micrograms | 0.1 to 0.15 mL |
Use an auto-injector if that is what is available. If there is no improvement in airway, breathing or circulation, repeat the IM dose after 5 minutes.
Immediate treatment step by step
Use the ABCDE approach and treat problems as you find them. The steps follow the Resuscitation Council UK algorithm. In the community, call 999 and say 'anaphylaxis'.
- Call for help early: Call the resuscitation team or 999 and ask for the emergency kit and adrenaline.
- Remove the trigger if possible: Stop any infusion or medicine that may be responsible. Scrape out a bee sting. Do not make the person vomit after a food trigger.
- Position the patient: Lie them flat, with or without legs raised, if they have circulatory problems. If breathing is difficult they may sit up, but must not stand or walk, as a sudden upright posture can cause cardiac arrest. Pregnant patients lie on their left side. Unconscious but breathing patients go in the recovery position.
- Give IM adrenaline: Give the age-appropriate dose into the outer thigh, through thin clothing if that saves time. Note the time.
- Repeat after 5 minutes if no better: Keep monitoring and give a further IM dose if airway, breathing or circulation problems persist.
- Support ABC: High-flow oxygen, IV or IO access in hospital, a rapid crystalloid bolus (Resuscitation Council UK advises 500 to 1,000 mL in adults and 10 mL/kg in children, repeated as needed), and monitoring with oximetry, blood pressure and ECG.
- Start CPR if needed: If the patient becomes unresponsive and is not breathing normally, start CPR and follow the advanced life support algorithm.
Many wards stock ampoules rather than auto-injectors. Read the label aloud, check it says 1 mg/mL, and draw up the volume with a 1 mL syringe so small volumes such as 0.15 mL are accurate. Use a needle long enough to reach muscle and inject at 90 degrees.
What is refractory anaphylaxis, and where do antihistamines and steroids fit?
Resuscitation Council UK defines refractory anaphylaxis as respiratory or cardiovascular problems that persist despite two appropriate doses of IM adrenaline. These patients need urgent expert help from critical care, anaesthetics or emergency medicine. Seek that help early, ideally after the first dose if the patient is not improving. Continue IM adrenaline every 5 minutes until an expert starts a low-dose IV adrenaline infusion, and give rapid fluid boluses.
Since the 2021 Resuscitation Council UK guideline, antihistamines are not part of initial emergency treatment. A non-sedating oral antihistamine may be used after stabilisation for skin symptoms. Routine corticosteroids are no longer advised; they may be considered after initial resuscitation in specific situations, such as ongoing asthma or shock, on expert advice.
A patient becomes wheezy and hypotensive after IV antibiotics. The nurse gives IV chlorphenamine and hydrocortisone, then waits 20 minutes to see if they work before calling for help.
The nurse stops the infusion, calls for help, lays the patient flat, gives 500 micrograms IM adrenaline into the outer thigh and notes the time. After 5 minutes the blood pressure is still low, so a second dose is given and the team starts IV fluids and seeks expert help.
Chlorphenamine and hydrocortisone act slowly and do not treat airway swelling or shock. Giving them first wastes the minutes that matter.
Special situations
- Pregnancy: give adrenaline at the usual dose, position on the left side and call obstetric help early, because maternal shock threatens the baby.
- Older adults and people with heart disease: give adrenaline. The risk of untreated anaphylaxis outweighs the risk of a correct IM dose.
- Beta-blockers: patients may respond less well and need further doses and early expert help.
- During anaesthesia: early signs may be hypotension, rising airway pressure or falling end-tidal carbon dioxide. Anaesthetists may use small IV doses in a fully monitored patient; this is a specialist skill. Elsewhere, IM adrenaline is correct.
- Auto-injector already used: if the patient used their own device and is not better after 5 minutes, give another dose.
Ten minutes after a vaccination, Ruth, 34, says her throat feels tight. Her voice is hoarse, she is wheezy and has hives on her neck. The pharmacist, Priya, asks a colleague to ring 999 and say 'anaphylaxis'. Ruth is breathless and wants to sit up, so Priya sits her on the floor against a wall and tells her not to stand. Priya gives 500 micrograms IM into the outer thigh and notes the time. After five minutes Ruth is still wheezy, so she gives a second dose. She hands over doses, times, the vaccine and batch number to paramedics, then completes a Yellow Card and an incident report.
After the emergency: tryptase, observation and discharge
NICE guideline NG258, published in May 2026 and replacing CG134, covers assessment and referral after emergency treatment and incorporates the Resuscitation Council UK's risk-based approach to observation.
- Mast cell tryptase: never delay treatment for it. In people aged 16 and over, NICE advises a sample as soon as possible after emergency treatment starts and a second ideally within 1 to 2 hours (no later than 4 hours) of symptom onset. Record sample times and onset time.
- Observation: the length depends on risk. A short period after resolution may be enough for a fast, full response to one early dose in a well-supported patient; longer observation (6 hours or more, sometimes 12) is advised after two doses, a previous biphasic reaction, severe asthma, late-night presentation or other higher-risk features. Follow local policy and the full current criteria.
- Before discharge: senior review, two in-date adrenaline auto-injectors with training (unless the trigger is an easily avoided medicine), written information, and advice to carry both devices at all times.
- Referral: offer referral to an age-appropriate specialist allergy service.
- Records: document the reaction and suspected trigger in the allergy record, tell the GP, and report suspected drug reactions to the MHRA Yellow Card scheme.
Allergic reaction to antibiotic. Treated. Now settled. Discharge with antihistamines.
Anaphylaxis 14:05, five minutes after IV co-amoxiclav: BP 82/50, HR 124, no rash. Infusion stopped, laid flat, IM adrenaline 500 micrograms left thigh 14:07, repeated 14:12 for persistent hypotension. 1,000 mL crystalloid. BP 118/72 by 14:30. Tryptase 14:20 and 15:30. Allergy recorded: co-amoxiclav, anaphylaxis. Observed per trust policy for two doses. Two auto-injectors prescribed, use demonstrated. Allergy clinic referral. Yellow Card submitted. GP informed.
Learning more
This guide is educational. Follow current Resuscitation Council UK anaphylaxis guidance, NICE NG258 and your local emergency procedures, and complete your organisation's mandatory anaphylaxis and resuscitation training. Know where the adrenaline is kept and which product is stocked in every area you work. The Anaphylaxis: Emergency Recognition and Treatment course works through recognition, dosing, refractory reactions and aftercare with emergency scenarios and a reflective exercise for your CPD record. Online learning does not replace accredited hands-on resuscitation training.
Frequently asked questions
What is the adult adrenaline dose for anaphylaxis?
Resuscitation Council UK recommends 500 micrograms of intramuscular adrenaline for adults and children over 12, which is 0.5 mL of 1 mg/mL (1:1,000) adrenaline. Give it into the outer thigh and repeat after 5 minutes if airway, breathing or circulation problems do not improve. An auto-injector can be used if that is what is available.
What dose of adrenaline is given to a child with anaphylaxis?
Resuscitation Council UK doses are 300 micrograms (0.3 mL of 1 mg/mL) for ages 6 to 12, 150 micrograms (0.15 mL) for 6 months to 6 years, and 100 to 150 micrograms for under 6 months. Small or prepubertal children over 12 may receive 300 micrograms. Use a 1 mL syringe for accuracy.
How often can you repeat adrenaline in anaphylaxis?
Repeat the intramuscular dose after 5 minutes if there is no improvement. If problems persist after two doses, the reaction is classed as refractory and needs urgent expert help. IM doses continue every 5 minutes until an expert starts an adrenaline infusion. Record the time of every dose.
Can you have anaphylaxis without a rash?
Yes. Skin changes are common but can be absent, subtle or appear late. Anaphylaxis is likely when sudden, rapidly progressing airway, breathing or circulation problems follow a possible trigger. Sudden hypotension after an IV antibiotic, even with clear skin, should be treated as anaphylaxis.
Are chlorphenamine and hydrocortisone still given for anaphylaxis?
Not as first-line emergency treatment. Since 2021 Resuscitation Council UK guidance, antihistamines are not part of initial treatment and routine corticosteroids are no longer advised. A non-sedating oral antihistamine may help skin symptoms once the patient is stable, and steroids may be considered in specific situations on expert advice.
Where should IM adrenaline be injected?
Into the anterolateral aspect of the middle third of the thigh, at 90 degrees, using a needle long enough to reach muscle. It can be given through thin clothing to save time. Auto-injectors are also designed for the outer thigh; hold them in place for the time stated on the device.
How long should a patient be observed after anaphylaxis?
It depends on risk. National guidance now uses a risk-based approach, with shorter observation after a quick, full response to one early dose and longer periods, often at least 6 or 12 hours, after two or more doses, previous biphasic reactions or other higher-risk features. Follow local policy and current NICE and Resuscitation Council UK criteria.
Related courses
Anaphylaxis: Emergency Recognition and Treatment
This course teaches you how to recognise anaphylaxis quickly and give intramuscular adrenaline without delay, following the Resuscitation Council UK…
Adult Advanced Life Support (UK Guidelines)
This course explains the recognition and management of adult in-hospital cardiac arrest, based on the current Resuscitation Council UK adult advanced…
Paediatric Life Support (UK Guidelines)
This course teaches the recognition of the seriously ill or injured child and the management of paediatric cardiorespiratory arrest, based on current…
Sources and further reading
- Emergency treatment of anaphylaxis: guidelines for healthcare providers. Resuscitation Council UK.
- Anaphylaxis: assessment and referral after emergency treatment (NG258). National Institute for Health and Care Excellence.
- Drug allergy: diagnosis and management (CG183). National Institute for Health and Care Excellence.
- Yellow Card scheme. Medicines and Healthcare products Regulatory Agency.
- Immunisation against infectious disease (the Green Book), chapter 8. UK Health Security Agency.
- Anaesthesia, surgery and life-threatening allergic reactions: 6th National Audit Project (NAP6). Royal College of Anaesthetists.
Practitioner Insight is an independent education provider. It is not affiliated with or endorsed by the GMC, MPTS, NMC, HCPC, GPhC or any NHS organisation, and this information is not legal advice. If you have been referred to a regulator, speak to your defence organisation, trade union or legal representative.
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