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Drug Allergy

Scope

Drug allergy can be immediate or delayed, and can be allergic or non-allergic.

Clinical history and documentation of the reaction is paramount.

For patients with suspected drug allergy document in the medical records

  1. The generic drug name
  2. The features and severity of the reaction
  3. The date the reaction occurred

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

NICE guidance on Drug allergy

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Signs and Symptoms

Immediate, rapidly evolving reactions

Anaphylaxis – a severe multi system reaction characterised by:
  • erythema, urticaria or angioedema
and
  • hypotension and/or bronchospasm
Anaphylaxis guidelines		 Onset usually less than 1 hour after drug exposure (previous exposure not always confirmed)
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		 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

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 suspected drug allergy, document their 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

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

  1. 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
  2. The suspected causative drug should be stopped immediately and avoided pending further investigation if necessary
  3. Promptly document the reaction thoroughly, with at minimum
    1. The drug name
    2. The signs, symptoms, and severity of the reaction
    3. The date the reaction occurred
  4. Explain the allergy to the patient, and documented in the medical records with appropriate details.
    1. If there is a clear history consider identification jewellery.
    2. Advise patients to avoid drugs identified from history as likely causes of reactions

Referral Criteria

  1. Suspected anaphylaxis
  2. A severe non-immediate cutaneous reaction
  3. NSAID reactions involving cardiorespiratory compromise or severe angioedema – see NICE Drug allergy for guidance.
  4. 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
  5. Suspected local anaesthetic allergy where a procedure involving local anaesthetic is needed
  6. Anaphylaxis or another suspected allergic reaction during or immediately after general anaesthesia - refer to Anaesthetics Allergy Clinic
  7. There is diagnostic uncertainty or multiple drugs were involved (especially where the reaction is systemic)

All information regarding reactions, timing and implicated drugs must be included in the referral

General anaesthetic drug reactions should be referred to Dr Paul Sice, Department of Anaesthesia at Derriford Hospital

Referral Instructions

Refer to Peninsula Immunology and Allergy Service

Refer via DRSS for NHS Devon patients

e-Referral Selection

  • Specialty: Allergy
  • Clinic type: Allergy
  • Service: DRSS-South Devon & Torbay-Allergy- Devon ICB - 15N

Referral Forms

DRSS Referral form

Torbay and South Devon seeking advice form

Patient Information

NICE guidelines CG183

onlinelibrary.wiley - for the management of drug allergy

Pathway Group

This guideline has been signed off on behalf of NHS Devon.

Publication date: March 2016

Updated: September 2023

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