Signs and allergic patterns of suspected drug allergy with timing of onset
Immediate, rapidly evolving 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) |
Non-immediate reactions without systemic involvement
- 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 |
Non-immediate reactions with systemic involvement
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
| |
With respect to DRESS, study evidence (2) found:
- most common drug causes were found to be antibiotics (74%) and anticonvulsants (21%)
- most common comorbidities were epilepsy (26%) and hypertension (26%)
A study analysed patients with DRESS reported through the US Food and Drug Administration Adverse Event Reporting System (FAERS) (3):
- total of 26 831 patients with DRESS were identified, of which 99.67% were classified as having a serious adverse reaction
- overall mortality was 6.9% (1846 deaths)
- female patients were more frequently affected than male patients
- adults aged 18–64 years represented the largest group
- allopurinol, lamotrigine and vancomycin were the most frequently suspected drugs, accounting for over 30% of reports
Reference:
- NICE (September 2014). Drug allergy: diagnosis and management of drug allergy in adults, children and young people
- Del Pozzo-Magana, BR, Rieder, MJ, Garcia-Bournissen, F, Lazo-Langner, A. Drug reaction with eosinophilia and systemic symptoms (DRESS): A tertiary care centre retrospective study. Br J Clin Pharmacol. 2022; 1- 8. doi:10.1111/bcp.15354
- Castellana E, Chiappetta MR. Drug rash with eosinophilia and systemic symptoms: descriptive analysis of pharmacovigilance. European Journal of Hospital Pharmacy Published Online First: 22 January 2026.