Improving detection and management of drug allergy.

Suspected adverse drug reactions may be subdivided on the basis of mechanism e.g. immunological (requiring sensitisation by previous exposure) versus nonimmunological; timing (e.g. immediate or delayed), or whether the phenomenon is dose dependent or not. In the NICE guideline the main approach is to classify the event according to whether it: is immediate (within an hour of drug administration) or delayed (hours or days); affects a single or multiple systems; is clinically severe/life threatening or not. An immediate, immunologically mediated, multisystem, life-threatening reaction would for example include anaphylaxis (type 1 or typically IgE- mediated hypersensitivity) especially if the clinical features (e.g. bronchospasm, hypotension) are suggestive. Serum mast cell tryptase should be tested ideally within two hours and certainly before four hours post reaction. Detailed investigation of suspected cases in a specialist clinic is ideally delayed for 4-6 weeks after the event. Adverse drug reactions need to be meticulously recorded and the patient fully informed. Documentation should include: date of reaction; drug name (chemical and generic); route of administration; time interval between first dose and event; and nature and severity of symptoms. Written guidance should be provided on which other chemically related drugs also need to be avoided. Specialist referral is indicated for: suspected anaphylaxis; severe/life- threatening episodes e.g. Stevens-Johnson syndrome; severe NSAID reactions with ongoing need for NSAID therapy; suspected penicillin allergy (if alternative antibiotics are not available); and problems related to general and local anaesthesia.