Different types (and timing) of drug allergic (allergy) reactions

• Anaphylaxis - a severe multi-system reaction characterised by:
  • erythema, urticaria or angioedema and
  • hypotension and/or bronchospasm
• Urticaria or angioedema without systemic features
• Exacerbation of asthma (for example, with non-steroidal anti-inflammatory drugs [NSAIDs])

Onset usually less than 1 hour after drug exposure (previous exposure not always confirmed)

• Widespread red macules or papules (exanthema-like)
• Fixed drug eruption (localised inflamed skin)

Onset usually 6-10 days after first drug exposure or within 3 days of second exposure

Drug reaction with eosinophilia and systemic symptoms (DRESS) or drug hypersensitivity syndrome (DHS) characterised by:

• widespread red macules, papules or erythroderma
• fever
• lymphadenopathy
• liver dysfunction
• eosinophilia

Onset usually 2-6 weeks after first drug exposure or within 3 days of second exposure

Toxic epidermal necrolysis or Stevens-Johnson syndrome characterised by:

• painful rash and fever (often early signs)
• mucosal or cutaneous erosions vesicles, blistering or epidermal detachment
• red purpuric macules or erythema multiforme

Onset usually 7-14 days after first drug exposure or within 3 days of second exposure

Acute generalised exanthematous pustulosis (AGEP) characterised by:

• widespread pustules
• fever
• neutrophilia

Onset usually 3-5 days after first drug exposure

Common disorders caused, rarely, by drug allergy:

• eczema
• hepatitis
• nephritis
• photosensitivity vasculitis

Time of onset variable