Nice | Diagnosis and management of drug allergy

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).

Non-Immediate with systemic involvement - There are quite a few different reactions that can occur. See the table in the guideline.

Are there any tests we can do to determine an allergy?

Basically no. Mast cell Tryptase can be done for suspected anaphylaxis in AE, but there isn't anything else. IgE is not advised outside of specialist settings.

NSAID allergy - what can we do?

If the patient has had just a mild reaction, you can trial a COX-2 at the lowest dose, with just a single dose on the first day. Patients should be warned that there is still a low risk of reaction.

What should be recorded when documenting an allergy?

  • What drug
  • What reaction
  • Indication used drug for
  • Date and time of reaction
  • No of doses taken or days before onset
  • Route of administration
  • What to avoid in future - advise people to carry a record of this with them

Adverse reactions (not allergies) should be documented separately

NICE advises that all prescriptions, whether hand written or printed should have somewhere for the patient's drug allergies to be documented. This will be quite a big change.

When should patients be referred for specialist advice?

  • Suspected anaphylactic reaction
  • Suspected DRESS / Stephens-Johnson Syndrome / Toxic Epidermal Necrolyis
  • Penicillin allergy if
    • Condition that can only be treated with penicillins
    • Are likely to need penicillins regularly
    • Also unable to take at least one other class of ABx due to suspected allergy
  • General Anaesthetic - if during or immediately afterwards
  • Local Anaesthetic - if need a procedure under LA and have suspected allergy
  • NSAID allergy - if had severe symptoms, eg anaphylaxis / severe angioedema / asthmatic reaction and are likely to need ongoing NSAID use

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