Introduction
It may appear soon after taking the medicine or later, and may occur on its own or together with angio-oedema. It is essential to distinguish a true allergic reaction from a non-allergic one, as this has major consequences for future prescriptions.
Symptoms
- Raised red or pink patches
- Intense itching
- Short-lived lesions that disappear in under 24 hours
- May reappear each time the medicine is taken
- Possible associated angio-oedema (lips, eyelids, face)
- Rarely: feeling faint or general symptoms
Causes
- Allergic (immunological, sometimes IgE-mediated)
- Non-allergic (direct histamine release, intolerance)
- Non-steroidal anti-inflammatory drugs (NSAIDs)
- Antibiotics
- Aspirin
- Opioids
- Contrast agents
- Certain injectable medicines
Diagnosis
- Detailed history (medicine, timing, recurrence)
- Analysis of the timeline of symptoms
- Checking for associated angio-oedema
- Ruling out other causes of urticaria
- Allergy work-up at a later date if necessary
Treatments
- Immediate withdrawal of the suspected medicine
- Non-sedating antihistamines (first-line treatment)
- Short course of corticosteroids for extensive forms
- Clinical monitoring
- Adrenaline auto-injector prescribed if there is a history of severe reaction
- reintroducing the medicine is contraindicated
Management
Confirm the mechanism (allergic or not)
Formally identify the medicine responsible
Avoid unnecessarily excluding a whole class of medicines
Suggest safe alternative medicines
Make future prescriptions safe