Lecture 9: Drug-induced Skin Disorders

Vocabulary flashcards covering key terms from notes on drug-induced skin disorders.

Drug-induced Skin ADRs

Unwanted effects of drugs on the skin; range from mild rashes to severe conditions such as Stevens–Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN).

Type A (Predictable) reactions

Dose-dependent, related to pharmacology; examples include corticosteroid-induced skin thinning and tetracycline-related photosensitivity.

Type B (Unpredictable) reactions

Not dose-dependent; immune-mediated or idiosyncratic; examples include allergic contact dermatitis and severe cutaneous adverse reactions.

Exanthematous (morbilliform) eruption

Most common skin ADR; symmetrical red macules/papules; typically appears 1–2 weeks after starting the drug.

Urticaria and angioedema

IgE-mediated or non-immune mast cell activation; onset within hours of exposure.

Fixed drug eruption

Well-demarcated erythematous patch that recurs at the same site with re-exposure.

Photosensitivity

Light-induced skin reactions; includes phototoxic (dose-dependent, sunburn-like) and photoallergic (immune-mediated) reactions.

Phototoxic reaction

Dose-dependent reaction that resembles an amplified sunburn after light exposure.

Photoallergic reaction

Immune-mediated reaction triggered by light exposure to a drug; requires sensitization.

Pigmentation changes

Drug-induced skin color changes; example: minocycline-associated hyperpigmentation.

Alopecia

Hair loss associated with certain drugs, including chemotherapy.

Nail changes

Nail findings such as onycholysis and discoloration due to drugs.

Stevens–Johnson Syndrome (SJS)

Severe cutaneous adverse reaction with prodrome (fever, sore throat), widespread erythema, blisters, mucosal involvement; mortality 10–30%; triggers include sulfonamides, anticonvulsants, allopurinol.

Toxic Epidermal Necrolysis (TEN)

More extensive form of SJS with widespread skin detachment and high mortality.

Prodrome (SJS/TEN)

Early symptoms like fever and sore throat preceding widespread dermatologic eruption.

DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms)

Latency 2–8 weeks; rash, fever, lymphadenopathy, eosinophilia, multi-organ involvement.

AGEP (Acute Generalised Exanthematous Pustulosis)

Acute pustular eruption with fever and leukocytosis; resolves after drug withdrawal.

Common SCAR triggers

Drugs frequently linked to severe cutaneous adverse reactions (e.g., sulfonamides, anticonvulsants, allopurinol).

Genetic predisposition (HLA alleles)

Certain HLA alleles increase SCAR risk (e.g., with carbamazepine/allopurinol).

Immunosuppression as a risk factor

Conditions like HIV infection increase susceptibility to SCARs.

Polypharmacy and elderly

Use of multiple medications and advanced age raise risk of skin ADRs.

High-dose or prolonged drug use

Increased exposure linked to higher risk of severe skin ADRs.

Management: withdrawal

Immediate withdrawal of the suspected drug.

Supportive care

Fluids, wound care, antihistamines, corticosteroids (when appropriate).

Hospitalisation for SCARs

ICU or burn unit care for severe cases.

Desensitisation

Rechallenge is avoided; desensitisation may be considered only in special cases (e.g., penicillin).

Prevention: avoid re-challenge

Do not re-expose patient to a suspected drug after an ADR.

Genetic screening

Screening for HLA alleles before certain drugs (e.g., HLA-B*1502 before carbamazepine in Asians).

Key takeaways

Most ADRs are mild; SCARs are rare but life-threatening; classification into predictable vs unpredictable aids management; pharmacists play a key role in counseling, reporting, and preventing recurrence.