Drug Allergy A Guide to Diagnosis and Management

Transcription

1 Drug Allergy A Guide to Diagnosis and Management (Version 1 April 2015) Author: Jed Hewitt Chief Pharmacist, Governance & Professional Practice Date of Preparation: April 2015 Date for next full Review: April 2018 Approved by the Trust Drugs & Therapeutics Group in April 2015 If you require this document in an alternative format, ie, easy read, large text, audio, Braille or a community language please contact the Pharmacy Team on (Text Relay calls welcome)

2 1. Introduction. 1.1 All drugs have the potential to cause side effects, also known as 'adverse drug reactions', but not all of these are allergic in nature. Other reactions are idiosyncratic, pseudo-allergic or caused by drug intolerance. The British Society for Allergy and Clinical Immunology (BSACI) defines drug allergy as an adverse drug reaction with an established immunological mechanism. The mechanism at presentation may not be apparent from the clinical history and it cannot always be established whether a drug reaction is allergic or non-allergic without investigation. This guidance defines drug allergy as any reaction caused by a drug with clinical features compatible with an immunological mechanism. 1.2 The commonest drug allergies are in response to antibiotics, (in particular peniciliins and cephalosporins) and non-steroidal anti-inflammatory drugs (NSAIDs) including aspirin. However, drug allergies are not as common as often believed. Whilst 10% of the general population claim to have a penicillin allergy, in reality less than 1% are truly allergic. 1.3 Allergic reactions to NSAIDs are much more common in those with asthma. 1.4 Drug allergy to psychotropic drugs is rare but is more commonly seen in response to anticonvulsant drugs. 2. Prevention. 2.1 Prevention of drug allergy is achieved by avoiding exposure to drugs for which the patient has known allergy or sensitivity and to those for which crosssensitivity is possible. This applies to prescribed medication and for those purchased without prescription. 2.2 When prescribing, great care must be taken to avoid prescribing drugs for which there is known patient allergy. Information sources for drug allergy status include: Medical notes Medical letters from specialist centres GP patient summaries Summary Care Records The patient The patient s carers / relatives 2.3 Ideally, allergy status should be confirmed before the first drug chart is completed on admission. 2.4 Allergy status or sensitivities to medication must be recorded on the drug chart, (inpatient and/or community long-acting injection chart), ideally by the prescriber when first writing up the chart. If this cannot be ascertained at the time of first writing up the chart the prescriber must complete the second section of the allergy box (inpatient chart) stating the allergy status is not yet ascertained. The medical team is ultimately responsible for completing the allergy status box as

3 soon as possible, but another healthcare clinician involved in the medicines management process may ascertain the status and sign instead of the prescriber, including their designation e.g. pharmacist. 2.5 When rewriting drug charts, allergies or sensitivities must be carried forward. 2.6 If there is a known allergy, the following signed and dated entries must be made in the patient s notes and on all drug charts: Generic name(s) of medicine(s), unless otherwise recommended by the BNF Nature of reaction(s) to ensure a true allergy is being described. 2.7 When administering medication it is vital that the allergy status of the patient be checked on every occasion, especially in relation to newly prescribed medication. If allergy status is not recorded every attempt should be made to ascertain and record this prior to administration. 2.8 Further to point 2.7, if a penicillin has been prescribed for a patient whose allergy status is not recorded, administration should not take place until the relevant information has been obtained and recorded. 3. Assessment Signs & allergic patterns of suspected allergy 3.1 When assessing a person presenting with a possible drug allergy, take a history and undertake a clinical examination. (The following boxes can be used as a guide when deciding whether to suspect drug allergy). Box 1 Immediate, rapidly evolving reactions: Anaphylaxis a severe multi-system reaction characterised by: erythema, urticaria or angioedema and hypotension and/or bronchospasm Onset is usually within an hour of drug exposure. (Previous exposure not always confirmed). Urticaria or angioedema without systemic features Exacerbation of asthma (eg. with NSAIDs). Glossary see section 11.

4 Box 2 Non-immediate reactions without systemic involvement: Widespread red macules or papules (exanthema-like) Fixed drug eruption (localised inflamed skin) Onset usually 6 to 10 days after first drug exposure or within 3 days of second exposure. Box 3 Non-immediate reactions with systemic involvement: Drug reaction with eosinophilia and systemic symptoms (DRESS) or drug hypersensitivity syndrome (DHS) characterised by: Onset usually 2 to 6 weeks after first drug exposure or within 3 days of second exposure. widespread red macules, papules or erythroderma fever lymphadenopathy liver dysfunction eosinophilia Toxic epidermal necrolysis or Stevens- Johnson syndrome characterised by: painful rash and fever mucosal or cutaneous erosions vesicles, blistering or epidermal detachment red purpuric macules or erythema multiforme Acute generalised exanthematous pustulosis ( AGEP) characterised by: Onset usually 7 to 14 days after first drug exposure or within 3 days of second exposure. Onset usually 3 to 5 days after first exposure. widespread pustules fever neutrophilia Common disorders caused, rarely, by drug allergy: Variable time of onset. eczema hepatitis nephritis vasculitis photosensitivity Glossary see section 11.

5 3.2 Clinicians should be aware that a reaction is more likely to be caused by drug allergy if it occurs during or after use of the drug and: the drug is known to cause that type of reaction the patient has previously had a similar reaction to the same drug or to another drug in the same class 3.3 Clinicians should be aware that a reaction is less likely to be caused by drug allergy if: there is a possible non-drug cause for the patient s symptoms eg. they have had similar symptoms when not taking the drug - or the patient only has gastrointestinal symptoms. 4. Documenting and sharing information. 4.1 Patients drug allergy status must be clearly recorded in their medical record. 4.2 Patients drug allergy status must also be recorded on the front of their drug chart(s) using the dedicated allergy box. This must be recorded on each chart in use and always carried forward when new charts are started. 4.3 If there is a drug allergy the following minimum information must be recorded: the (generic) drug name the signs, symptoms and severity of the reaction the date when the reaction first occurred (if known) 5. Documenting new suspected drug reactions 5.1 When a patient presents with a suspected drug allergy, the reaction must be clearly recorded in the medical notes including: the generic (and proprietary) name of the drug suspected of causing the reaction the strength, formulation and route of the drug a description of the reaction see section 3 the diagnosis / illness the drug was being taken for the date and time of the reaction the number of doses taken or the number of days on the drug before the onset of the reaction 5.2 The patient s GP should be consulted / informed at the earliest opportunity. 6. Maintaining and sharing drug allergy information 6.1 Drug allergy status should be documented separately from adverse drug reaction information so that it remains clearly visible to all prescribers.

6 6.2 Where possible, patients drug allergy status should be confirmed with the patient or with their carers before prescribing or administering any drug. Alternative information sources such as Summary Care Records and GP Summaries should also be used routinely. 6.3 Confirmation of drug allergy status must be considered a routine part of medicines reconciliation at the time of admission to any inpatient unit. 6.4 Information about allergy status must be kept updated and must be included in all hospital discharge letters, specialist referral letters and GP referral letters. 7. Providing information and support to patients 7.1 Clinicians must ensure patients (and their carers) are aware of the drugs or drug classes that they need to avoid. They should be advised to check with the pharmacist before taking any over-the-counter medicines. 7.2 Clinicians should advise patients (and their carers) to carry information about their drug allergy with them at all times and to share this with any healthcare professional that is treating them, eg. hospital doctor, GP, dentist, pharmacist, nurse. 8. Non-specialist management and referral to specialist services 8.1 If a drug allergy is suspected: Consider stopping the drug(s) suspected to have caused it and advise the patient that they should avoid that drug in the future. Where possible, treat the symptoms of the acute reaction if not severe. Send patients with a severe reaction to the nearest casualty department, by ambulance if necessary. Fully document the incident in the patient s medical notes see section 5. When appropriate, provide the patient (and their carers) with the information. 8.2 If a patient has an anaphylactic reaction they should still be immediately referred to the nearest casualty department (dial 999), even if the reaction appears to have been successfully treated by administering adrenaline injection. 8.3 Following an anaphylactic reaction, Trust services should follow up with acute hospital services to ensure the patient receives a referral to a specialist drug allergy service. This should also occur following any severe non-immediate cutaneous reaction eg, Stevens-Johnson syndrome or epidermal necrosis.

7 9. Non-steroidal anti-inflammatory drugs (NSAIDs) 9.1 If patients have had a mild allergic reaction to a NSAID but still need an antiinflammatory, consideration can be given to using a selective COX-II inhibitor as these carry a lower risk of allergy. However, those prescribing and administering must remain aware that there is still some risk of cross sensitivity, so a low starting dose should be used and administration should only be once daily. 10. Beta-lactam antibiotics eg. penicillins, cephalosporins 10.1 Patients with a suspected drug allergy to a beta-lactam antibiotic should be referred to a specialist drug allergy service if: they need treatment for an illness that can only be treated by beta-lactam antibiotic, and/or they are likely to need a beta-lactam antibiotic frequently in the future. 11. Glossary Angioedema Epidermal necrolysis Eosinophilia Erythema Erythroderma Exanthema Lymphadenopathy Macules Nephritis Papules Pustules Urticaria Vasculitis Swelling of skin and/or mucous membranes Potentially life-threatening separation of skin layers Raised eosinophil count (>450µL) Redness of skin and/or mucous membranes Widespread inflammation of the skin Widespread rash Swollen lymph glands (or other abnormality) Flat discoloured areas of skin Inflammation of the kidneys Raised discoloured areas of skin Small, fluid-filled skin eruptions Raised itchy rash Inflammation of blood vessels Reference: NICE Clinical Guideline 183 (September 2014): Drug allergy diagnosis and management in adults, children and young people. Cross reference: Trust Medicines Code (2014/15) Section 4.