Adverse Drug Reactions (ADRs)

An adverse drug reaction (ADR) is any harmful, unintended response to a medicine that occurs at doses normally used in people to prevent, diagnose or treat disease, or to modify a physiological function. In dermatology and medical aesthetics, the skin is the organ where ADRs show up most often (30% to 45% of all systemic ADRs). That is because of its large surface area, rich network of small blood vessels and abundance of antigen-presenting cells (Langerhans cells and dendritic cells).

Drug-related skin reactions range widely, from mild, self-limiting rashes (hives, maculopapular eruptions) to acute, life-threatening syndromes (SJS/TEN, DRESS, AGEP). At Haute-Derma, early recognition, accurate classification of the underlying mechanism and prompt treatment are central to keeping patients safe, and they form the basis of a personal drug allergy record.

Mechanisms and the Rawlins & Thompson Classification

Clinically, ADRs fall into two main groups under the modified Rawlins & Thompson classification, depending on whether the reaction is predictable:

  • Type A ADRs (Augmented):
    • Mechanism: dose-dependent reactions arising from the drug's known pharmacologic effects. They account for about 80% of clinical ADRs.
    • Features: predictable from pharmacokinetics and pharmacodynamics. Common, but rarely fatal.
    • Skin examples: dry skin and lips with high-dose isotretinoin, skin thinning and visible vessels from long-term topical steroids, and hair loss from chemotherapy.
  • Type B ADRs (Bizarre — idiosyncratic or allergic):
    • Mechanism: not dose-dependent; driven by the immune system (drug allergy) or by genetic and individual susceptibility (idiosyncrasy).
    • Features: cannot be predicted from the drug's usual pharmacology. Less common, but often severe, with a high death rate. Activated T cells or IgE- or immune complex-mediated responses play the central role.
    • Gell & Coombs classification (for type B drug allergy):

How We Diagnose and Screen for ADRs at Haute-Derma

  • Detailed Drug History and Timeline
    • Building a timeline: we record the exact start date, any dose changes and the date the rash appeared for every oral and injected medicine, supplement and herbal product used in the past 2 months.
    • Assessing causality with the Naranjo scale or the ALDEN score (specific to SJS/TEN), based on plausible timing, what happens when the drug is stopped (dechallenge) and, where data exist, what happens on re-exposure (rechallenge).
  • Clinical Examination and Lab Tests
    • Checking the mucous membranes (eyes, mouth, genitals) and the Nikolsky sign (the top layer of skin shearing off with gentle rubbing).
    • Complete blood count: looking for a sharp rise in eosinophils, atypical lymphocytes or low platelets.
    • Liver (ALT/AST), kidney (urea/creatinine) and muscle enzyme tests to pick up internal organ involvement early.
  • Identifying the Culprit After the Acute Phase
    • Skin prick and intradermal tests: for type I (IgE) reactions, performed 4–8 weeks after the skin has fully healed.
    • Patch testing: chambers containing the suspected drugs are left on the skin for 48 hours to diagnose delayed, T cell-mediated (type IV) allergy.

Principles of ADR Management

  • Stop the Suspected Drug Immediately: as soon as an ADR is suspected, stopping the culprit — or all non-essential medicines — is the single most important step in reducing the risk of severe complications and death.
  • Supportive and Intensive Care
    • Severe cases (SJS/TEN, DRESS) need care in a sterile isolation room or an intensive care or burn unit.
    • Correcting fluids and electrolytes, maintaining body temperature, and caring for skin and mucous membranes with non-stick petrolatum gauze dressings.
  • Drug Treatment to Calm the Immune Response
    • Systemic corticosteroids: IV methylprednisolone (1–2 mg/kg/day) given early in DRESS or in moderate to severe drug reactions to control the excessive inflammatory response (cytokine storm).
    • Intravenous immunoglobulin (IVIG) and cyclosporine A: used in SJS/TEN to block the Fas–FasL pathway that drives widespread death of epidermal keratinocytes.
    • Second-generation antihistamines: to control itching and hives.
  • Formal ADR Reporting and Patient Alerts
    • Completing a standard ADR report for the National ADR Reporting Center.
    • Giving the patient a personal "Drug Allergy Card" listing the drug that caused the reaction and any cross-reacting drugs to be strictly avoided in the future.

Types of Drug Reactions

Exanthematous Eruptions

The most common delayed (type IV) drug hypersensitivity, often caused by beta-lactams or anticonvulsants. Itchy pink-red macules and papules spread symmetrically over the body, appearing 7–14 days after starting the drug.

Urticarial Eruptions

An immediate (type I) reaction, either IgE-mediated or from direct histamine release (e.g., antibiotics, NSAIDs). Intensely itchy pink-red wheals appear quickly, with each one fading within 24 hours.

Pustular and Acneiform Eruptions

Acute generalized exanthematous pustulosis (AGEP) or acne-like eruptions from corticosteroids, lithium or EGFR inhibitors. Shows as many tiny sterile pustules on red skin, or uniform pustular papules without blackheads on the face and back.

Bullous Eruptions

Severe reactions including Stevens-Johnson syndrome (SJS), TEN and drug-induced pemphigoid. Tense blisters or widespread epidermal necrosis, skin that shears off (positive Nikolsky sign) and erosions of multiple mucous membranes.

Fixed Drug Eruptions

A reaction that recurs at exactly the same spot each time the culprit drug is taken (co-trimoxazole, tetracyclines, NSAIDs). A round or oval red patch, sometimes blistering in the center, that heals with long-lasting dark pigmentation.

Drug-Induced Hyperpigmentation

Build-up of melanin or deposits of drug complexes or metals in the dermis (e.g., amiodarone, minocycline, antimalarials). The skin turns blue-gray, brown-black or slate-gray, mainly on sun-exposed areas.

Drug-Induced Lichenoid Eruptions

A lichen planus-like reaction to drugs such as antimalarials, beta-blockers and ACE inhibitors. Flat-topped, raised, violet, finely scaly and itchy papules, mostly on the trunk, with little mucosal involvement.

Drug-Induced Cutaneous Pseudolymphoma

A benign lymphocyte proliferation that mimics cutaneous lymphoma, triggered by drugs such as anticonvulsants or antihypertensives. Firm, brick-red nodules or plaques, single or multiple, that clear once the drug is stopped.

Drug-Induced Lupus and Dermatomyositis

A drug-triggered autoimmune syndrome (hydralazine, procainamide, statins, biologics). Butterfly rash, photosensitive rash, Gottron papules, joint pain or muscle weakness, with positive anti-histone antibodies in the blood.

Purpuric Eruptions

Inflammation of small skin blood vessels from immune complex deposition (sulfonamides, allopurinol). Raised purple spots (palpable purpura) that don't blanch on pressure, mainly on the lower legs.

Anticoagulant-Induced Skin Necrosis

Acute blockage of small skin vessels in the first days of warfarin treatment, caused by a rapid fall in protein C. Painful bruise-like patches that quickly turn black and necrotic in fatty areas such as the thighs, buttocks and breasts.

Neutrophilic Eccrine Hidradenitis

Direct toxic injury to the sweat glands from cancer chemotherapy. Painful, swollen red papules and plaques that flare with fever, mainly on the trunk, face and limbs.

Frequently Asked Questions

Experiencing similar symptoms?

Our Haute-Derma specialists are ready to provide expert consultation on Adverse Drug Reactions (ADRs) — from accurate diagnosis to the most suitable treatment plan for you.

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