Drug Allergy (Adult) Care Pathway

Review in progress

Disclaimer: The guidance contains helpful primary care information for management of referrals and up to date referral criteria. These guidelines are locality specific to best reflect local services. This guidance does not override or replace the individual responsibility of healthcare and social care professionals involved in the delivery of care to make informed professional judgements appropriate to the circumstances of the individual.


This guidance refers to:

  • A drug allergy that can be immediate or delayed, and can be allergic or non-allergic
  • Adults and children


Signs and Symptoms

Immediate, rapidly evolving reactions
  • Anaphylaxis
    • a severe multi system reaction characterised by erythema, urticaria or angioedema and hypotension and/or bronchospasm
    • Onset usually less than 1 hour after drug exposure (previous exposure not always confirmed)
    • See Anaphylaxis guidelines
  • Urticaria or angioedema without systemic features
    • Onset usually less than 1 hour after drug exposure (previous exposure not always confirmed)
  • Exacerbation of asthma (for example, with non steroidal anti inflammatory drugs [NSAIDs)
    • Onset usually less than 1 hour after drug exposure (previous exposure not always confirmed)
Non‑immediate reactions without systemic involvement
  • Widespread red macules or papules (exanthema like)
    • Onset usually 6–10 days after first drug exposure or within 3 days of second exposure
  • Fixed drug eruption (localised inflamed skin)
    • Onset usually 6–10 days after first drug exposure or within 3 days of second exposure
Non‑immediate reactions with systemic involvement
  • Drug reaction with eosinophilia and systemic symptoms (DRESS) or drug hypersensitivity syndrome (DHS) characterised by:
      • widespread red macules, papules or erythroderma
      • fever
      • lymphadenopathy
      • liver dysfunction
      • eosinophilia
    • Onset usually 2–6 weeks after first drug exposure or within 3 days of second exposure
  • Toxic epidermal necrolysis or Stevens–Johnson syndrome characterised by:
    • painful rash and fever (often early signs)
    • mucosal or cutaneous erosions
    • vesicles, blistering or epidermal detachment
    • red purpuric macules or erythema multiforme
  • Acute generalised exanthematous pustulosis (AGEP) characterised by:
    • widespread pustules
    • fever
    • neutrophilia
  • Onset usually 3–5 days after first drug exposure

A drug reaction is more likely if it occurred during or after use of the drug and:

  • the drug is known to cause that type of reaction or
  • the person has previously had a similar reaction to that drug or drug class

A drug reaction is less likely if:

  • there is a possible non drug cause for the person's symptoms (for example, they have had similar symptoms when not taking the drug) or
  • there were gastrointestinal symptoms only


Clinical history and documentation of the reaction is paramount

When a person presents with suspected drug allergy, document their reaction in a structured approach (NICE guidance recommendation 1.2.3) including:

  • The generic and proprietary name of the drug or drugs suspected to have caused the reaction, including the strength and formulation
  • A description of the reaction
  • The indication for the drug being taken (if there is no clinical diagnosis, describe the illness)
  • The date and time of the reaction
  • The number of doses taken or number of days on the drug before onset of the reaction
  • The route of administration
  • Which drugs or drug classes to avoid in future


Undertake the following to aid diagnosis, inform management or prior to referral:

  • None recommended prior to referral.
  • Specific IgE (RAST) testing to drugs should not be used in a non-specialist setting (NICE guidelines).


Anaphylaxis should be treated immediately according to Resuscitation Council guidelines. Acute measurement of mast cell tryptase (immediately and 2 hours after the onset of symptoms) should be performed.

If drug allergy suspected:

  • The suspected causative drug should be stopped immediately and avoided pending further investigation if necessary
  • Treat the symptoms of the acute reaction if needed; send people with severe reactions to hospital
  • Promptly document the reaction thoroughly, with at minimum
    • The drug name
    • The signs, symptoms, and severity of the reaction
    • The date the reaction occurred
  • Explain the allergy to the patient, and documented in the medical records with appropriate details
    • If there is a clear history consider identification jewellery
    • Advise patients to avoid drugs identified from history as likely causes of reactions


Referral Criteria

  • Suspected anaphylaxis
  • A severe non-immediate cutaneous reaction
  • NSAID reactions involving urticaria, angioedema, or an asthmatic reaction to a non-selective NSAID
  • Beta lactam allergy when
    1. Beta lactams are considered essential for management
    2. There is likely to be frequent need for beta-lactam antibiotics in the future (e.g. recurrent bacterial infections or immune deficiency)
    3. There is suspected allergy to at least one other class of antibiotics in addition to beta lactams
  • Suspected local anaesthetic allergy where a procedure involving local anaesthetic is needed
  • Anaphylaxis or another suspected allergic reaction during or immediately after general anaesthesia
  • There is diagnostic uncertainty or multiple drugs were involved (especially where the reaction is systemic)

Referral Requirements

  • Information regarding reactions, timing and implicated drugs must be included in the referral.

Referral Instructions

  • e-Consultation is not available for this speciality
  • Referrals should be made via ICG to TRISH (if training has been undertaken) - See user guides (EMIS & S1) for further information.
  • For those Practices who have not received ICG training referrals to the Clinical Immunology Paediatric Allergy Clinic via eRS
  • Please identify speciality and clinic type

Supporting Information

Shared Decision Making

  • Patients have a right to make decisions about their care and should be fully informed about the options they face. They should be provided with reliable evidence-based information on the likely benefits and harms of interventions or actions, including any uncertainties and risks, eliciting their preferences and supporting implementation

Patient information/Public Health/Self Care

Evidence/additional information

Assurance & Governance

  • This guidance was developed on: 10.2017
  • This Care Pathway was ratified by: The OSCAR Assurance Group
  • Date ratified: 10.2017
  • Publication Date: 12.2017
  • Review Date: 10.2018
  • Ref No: AL6 - 03.2017
Any feedback or suggestions to improve this guidance should be sent to: oscaradmin@this.nhs.uk
Only the electronic version is maintained, once printed this is no longer a controlled document


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