Drug Reactions and Drug-Induced Skin Disease

Exanthematous (Maculopapular) Eruption

Features

•    Most common type of drug rash

•    Delayed type IV hypersensitivity (usually appears 5–14 days after starting drug)

•    Symmetrical, diffuse erythematous macules and papules

•    Typically starts on trunk → spreads peripherally

•    No mucosal involvement

Common culprit drugs

•    Penicillins, cephalosporins

•    Sulfonamides

•    Anticonvulsants (e.g., phenytoin, carbamazepine)

Management

•    Stop offending drug

•    Symptomatic relief (topical steroids, antihistamines)

Urticaria and Angioedema

Features

•    Immediate (Type I) hypersensitivity

•    Urticaria: transient wheals, itching, resolves <24 h

•    Angioedema: deeper swelling, can involve airway (emergency)

Common culprit drugs

•    Penicillins

•    NSAIDs

•    Contrast media

•    ACE inhibitors (angioedema without urticaria — bradykinin-mediated)

Management

•    Stop drug

•    Antihistamines ± corticosteroids

•    Epinephrine if anaphylaxis suspected

Fixed Drug Eruption

Features

•    Well-defined erythematous or violaceous plaques

•    Recur at exact same site with re-exposure

•    Common sites: lips, genitals, hands

Common culprit drugs

•    NSAIDs

•    Tetracyclines

•    Sulfonamides

Management

•    Avoid culprit drug

•    Topical corticosteroids

Severe Cutaneous Adverse Reactions (SCARs)

Stevens–Johnson Syndrome (SJS) / Toxic Epidermal Necrolysis (TEN)

•    Spectrum of same disease (SJS <10% BSA; TEN >30% BSA)

•    Extensive epidermal necrosis and detachment, mucosal involvement (>90% cases)

•    Positive Nikolsky’s sign

•    High mortality (TEN ~30–50%)

Common culprit drugs

•    Allopurinol

•    Anticonvulsants (lamotrigine, carbamazepine, phenytoin)

•    Sulfonamides

•    Nevirapine

•    NSAIDs (oxicams)

Management

•    Stop drug immediately

•    Supportive care in burns/ICU setting

•    IV fluids, wound care, infection prevention

DRESS syndrome (Drug Reaction with Eosinophilia and Systemic Symptoms)

•    Fever, facial oedema, widespread rash

•    Eosinophilia, atypical lymphocytes

•    Organ involvement: liver (most common), kidney, lung

Common culprit drugs

•    Anticonvulsants

•    Allopurinol

•    Sulfonamides

Management

•    Stop drug

•    Systemic corticosteroids (in severe cases)

AGEP (Acute Generalised Exanthematous Pustulosis)

•    Numerous sterile, non-follicular pustules on erythematous background

•    Often starts in intertriginous areas

•    Associated fever, neutrophilia

•    Resolves rapidly after stopping drug

Common culprit drugs

•    Aminopenicillins

•    Macrolides

•    Calcium channel blockers

Management

•    Stop drug

•    Supportive treatment

Photosensitivity Reactions

Types

•    Phototoxic (more common): exaggerated sunburn

•    Photoallergic: eczematous reaction (type IV hypersensitivity)

Common culprit drugs

•    Tetracyclines (especially doxycycline)

•    Thiazides

•    Amiodarone

•    Fluoroquinolones

•    NSAIDs (piroxicam)

Management

•    Sun avoidance, protective clothing, high-factor sunscreen

•    Stop offending drug if possible

Extra Revision Pearls

•    Nikolsky’s sign positive → think SJS/TEN, pemphigus vulgaris

•    DRESS: remember eosinophilia and hepatitis clue

•    AGEP: rapid onset pustules, resolves quickly after stopping drug

•    ACE inhibitor angioedema: bradykinin-mediated, not responsive to antihistamines/steroids