Drug Allergy

When to consider referral


1.    Suspected anaphylaxis. Please include in the referral any preferred alternative classes of medication which could be considered in order to facilitate management to facilitate more directed investigations.

2. Non-immediate cutaneous reaction where that class of drug is considered essential to management.

3.    A severe non-immediate cutaneous reaction.  Please include in the referral any preferred alternative classes of medication which could be considered to facilitate more directed investigations.

4.    NSAID reactions involving urticaria, angioedema, or an asthmatic reaction to a  non-selective NSAID

5.    Beta lactam allergy when

a.    Beta lactams are considered essential for management

b.    There is likely to be frequent need for beta-lactam antibiotics in the future (eg recurrent bacterial infections or immune deficiency)

c.    There is suspected allergy to at least one other class of antibiotics in addition to beta lactams

6.    Suspected local anaesthetic allergy where a procedure involving local anaesthetic is needed

7.    Anaphylaxis or another suspected allergic reaction during or immediately after general anaesthesia. These referrals should be sent to the Anaesthetic Allergy Service inbox at:  plh-tr.PlymouthAnaestheticAllergyService@nhs.net

8.    There is diagnostic uncertainty or multiple drugs were involved (especially where the reaction is systemic)



Primary care management prior to referral


1.    Anaphylaxis should be treated immediately according to Resuscitation Council guidelines.


2.    The suspected causative drug should be stopped immediately.


Clinical history and documentation of the reaction is paramount.


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


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

a.    the generic and proprietary name of the drug or drugs suspected to have caused the reaction, including the strength and formulation

b.    a description of the reaction

c.    the indication for the drug being taken (if there is no clinical diagnosis, describe the illness)

d.    the date and time of the reaction

e.    the number of doses taken or number of days on the drug before onset of the reaction

f.     the route of administration

g.    which drugs or drug classes to avoid in future


Document all new reactions promptly and thoroughly to assist in future investigation.


NICE guidance on drug allergy


3.    Explain the allergy to the patient, and documented in the medical records with appropriate details.

a.    If there is a clear history consider identification jewellery.

b.    Advise patients to avoid drugs identified from history as likely causes of reactions



Immediate, rapidly evolving reactions

Anaphylaxis – a severe multi-system reaction characterised by:

•      erythema, urticaria or angioedema


•      hypotension and/or bronchospasm


See separate guidance for anaphylaxis

Onset usually less than 1 hour after drug exposure (previous exposure not always confirmed)

Urticaria or angioedema without systemic features

Exacerbation of asthma (for example, with non-steroidal anti-inflammatory drugs [NSAIDs)


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)


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

Onset usually 7–14 days after first drug exposure or within 3 days of second exposure

Acute generalised exanthematous pustulosis (AGEP) characterised by:

•      widespread pustules

•      fever

•      neutrophilia

Onset usually 3–5 days after first drug exposure




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


Clinic options available


We have no Choose and Book slots available – we review and triage all referrals ourselves and allocate clinics appropriately.


Review Date                            13/08/2019

Next Review Date                    13/08/2020

Author                                      Dr Andrew Whyte, Consultant Allergist and Immunologist, Derriford Hospital.

GP Sifter                                                Dr Isabel Boyd


Version No.  3.1