Drug allergy: diagnosis and management in GP

2nd October 2014 by Louise Hudman

Drug allergy: diagnosis and management in GP

This is a new guideline from NICE which tries to rationalise how we manage potential drug allergy. There is a useful section on when to refer to a specialist and there is also a good outline of what different reactions may look like. Sadly it can’t answer that question of whether the kid with a rash on d8 of his amoxicillin has a drug reaction or a viral rash.

Why is this an issue?

  • Penicillin allergy – 10% of the population think they are penicillin allergic – but only 1% actually are
  • NSAID allergy – affects up to 10% of those with asthma (it is very likely if they have nasal polyps too – though not if they have used NSAIDs in the last 12m with no problems) and 1/3 of those with chronic urticaria
  • Anaphylaxis – affects 1 in 1000 people
  • Intolerances – are often coded as allergy, leading to unnecessary avoidance in future

Patterns of Reaction

What is more likely to be a reaction?

  • Occurred during or after drug use (er – yes – pretty obvious that one I would have said!)
  • Patient previously had a similar reaction

What is less likely to be a reaction?

  • The patient has had similar reactions before, without the drug use
  • Just GI symptoms

What different kinds of reactions can you get?

Immediate – eg anaphylaxis, urticaria, angioedema, exacerbation of asthma (normally happen within an hour of use)

Non-Immediate with no systemic involvement – eg rash or fixed drug eruptions (these normally happen 2-6d after first use and 3d after subsequent use).

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