Felis ISSN 2398-2950

Drug eruption

Introduction

• Cause: idiosyncratic reaction to the use of a drug.
• Signs: may mimic any other cutaneous reaction pattern.
• Diagnosis: history of drug administration and response to drug withdrawal.
• Treatment: supportive care and drug withdrawal.
• Prognosis: mostly good.

Pathogenesis

Etiology

• Any drug can cause any reaction pattern.

Pathophysiology

• Mechanism of drug reactions is poorly understood.
• There may be the induction of an immune response or abnormality of drug metabolism in an individual.
  • Hypersensitivity reaction if the drug, a carrier molecule or a metabolite acts as an antigen.
    • Hypersensitivity reactions can be types 1,2,3 or 4.
    • Type 1-anaphylaxis or urticaria.
    • Type 2-cytotoxic reactions eg erythema multiforme.
    • Type 3-immune complex development   →   vasculitis.
    • Type 4-delayed type eg contact reactions.
  • Pseudoallergy where a drug causes mast cell or basophil degranulation in a non-immune-mediated fashion.
  • Autoimmunity: drugs may cause an alteration in autoantigens, there may be molecular mimicry or antigen-independent T-helper cell activation.
  • Rarely drug metabolites are directly toxic to skin cells, possibly as a consequence of a genetic enzyme deficiency in an individual.

Timecourse

• Most reactions occur within 1-3 weeks of drug exposure.

Diagnosis

Treatment

Prevention

Outcomes