Page 0 Drug Allergy Alice Oborne PhD, Consultant pharmacist-safe medication practice and MSO Medicines Use and Safety Network, 6 November 2014 Objectives • Demographics • Immediate and delayed reactions • Allergy questions – Allergy vs ADR • Documentation • Written information to patients • Referrals for allergy testing • Steps to keep us all safe – “Stop and check” Allergy vs adverse drug reaction: definitions Allergy • Inappropriate immune-mediated response to a harmless substance Drug allergy: … immune-mediated reaction to medicinal product Current draft NICE guideline definition • …Any reaction caused by a drug with clinical features compatible with an immunological mechanism Differs from Adverse Drug Reaction: • An unwanted or harmful reaction experienced following the administration of a drug or combination of drugs under normal conditions of use, suspected to be drug related
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Page 0
Drug Allergy
Alice Oborne PhD,
Consultant pharmacist-safe medication practice and MSO
Medicines Use and Safety Network, 6 November 2014
Objectives
• Demographics
• Immediate and delayed reactions
• Allergy questions – Allergy vs ADR
• Documentation
• Written information to patients
• Referrals for allergy testing
• Steps to keep us all safe
– “Stop and check”
Allergy vs adverse drug reaction: definitions
Allergy
• Inappropriate immune-mediated response to a harmless substance
Drug allergy: … immune-mediated reaction to medicinal product
Current draft NICE guideline definition
• …Any reaction caused by a drug with clinical features compatible with an immunological mechanism
Differs from Adverse Drug Reaction:
• An unwanted or harmful reaction experienced following the administration of a drug or combination of drugs under normal
conditions of use, suspected to be drug related
Page 3Drug allergy: demographics
• Most commonly due to penicillins
• No precise prevalence data
• 10-20% of hospitalised patients report a penicillin allergy
– Of these 1-10% are genuinely allergic
• Penicillin causes 0.7% to 10% of all cases of anaphylaxis
• Risk of anaphylaxis is 0.004% and 0.015% for each course
National data from NRLS, April 12 - March 13
15907Total
12287No Harm
2771Low
828Moderate
14Severe
7Death
Number of reportsDegree of Harm to Patient
With thanks to D Cousins and C Rosario, NHSE
100%15907Grand Total
<1%27Supply or use of over-the-counter medicine
<1%71Advice
1%232
Preparation of medicines in all locations /
dispensing in a pharmacy
2%267Monitoring / follow-up of medicine use
4%647Other
46%7288Administration / supply from a clinical area
46%7375Prescribing
Percentage (%)
Number of
reportsMedication Process
National data 2, Stage of Medication Use Process
77Grand Total
1Incorrect documentation of drug allergy
5No known previous drug allergy
15Unclear if previous unknown allergic reaction
56 (73%)
Drug prescribed/administered even with documented
allergy
Frequency
Did an error occur when the patient had a previous
known allergy?
National data 3, Thematic analysis: allergy known?
77Grand Total
1Antiplatelet
1Metoclopramide
1Alcohol wipes
1Xray contrast
1Antihistamine
1Penicillamine
1Gelofusine
1Plasma substitute
1Anti-epileptic
2Excipient
2Chemotherapy/ Cytotoxic
2Unknown
1Codeine
5Anaesthesia
2NSAID
5Opioid
1Tetracycline
1Trimethoprim
3Cephalosporin
44 (57%)Penicillin
FrequencyTherapeutic Group
National data 4, Thematic analysis: Drug involved
1. Immediate reactions, rapidly evolving: anaphylaxis; urticaria or
angiooedema with hypotension or bronchospasm
2. Non-immediate reactions without systemic involvement
• Acute generalised exanthematous pustulosis or fixed drug eruptions
3. Non-immediate reactions with systemic involvement
• Drug reaction with eosinophilia and systemic symptoms (DRESS)
• Drug hypersensitivity syndrome (DHS)
• Toxic epidermal necrolysis (TEN)
• Stevens-Johnson syndrome (SJS)
4. Common disorders caused rarely by drug allergy
• Eczema, hepatitis, photosensitivity, vasculitis
Practical classification of drug allergy Page 8
• Usually type I hypersensitivity
• Occur quickly after a single dose of drug
• Mast cell degranulation, releasing histamine
• Anaphylaxis
• Urticaria
• Angioedema
• Airway compromise
• Or hypotension
Classification1. Immediate reactions Page 9
Classification2. Non-immediate reactions
• Type IV hypersensitivity
• Can take 6-10 days to develop (earlier with subsequent exposures)