Introduction
Unlike immediate reactions, they are not IgE-mediated but involve cell-mediated mechanisms (type IV immunity). They mostly affect the skin, but can sometimes be severe and require specialist care.
Symptoms
- Widespread maculopapular rash
- Eczema-like patches
- Generalised redness
- Itching of varying intensity
- Peeling
- Possible involvement of the mucous membranes (severe forms)
- Fever or feeling generally unwell in some cases
Causes
- Delayed (type IV) hypersensitivity reaction
- Gradual sensitisation to the medicine
- Non-IgE-mediated mechanism
- Reaction sometimes only after several days of treatment
- Antibiotics
- Anti-epileptics
- Allopurinol
- Anti-inflammatories
- Topical medicines
- Certain long-term treatments
Diagnosis
- Detailed history (precise timeline)
- Review of all medicines taken
- Skin examination
- Ruling out an infectious or toxic cause
- Specialist allergy tests once the reaction has settled: Drug patch tests Delayed-reading skin tests Controlled challenge tests (selected cases)
- Drug patch tests
- Delayed-reading skin tests
- Controlled challenge tests (selected cases)
Treatments
- Permanent withdrawal of the suspected medicine
- Topical or systemic corticosteroids depending on extent
- Antihistamines for itching
- Close clinical monitoring
- Hospital admission for severe forms
- contraindicated
Management
Identify precisely which medicine is responsible
To avoid unnecessary exclusions
To make future treatment safe
To distinguish benign forms from serious ones
To provide an official medical report