Adverse Drug Reactions, Drug Eruptions, and Drug Allergy

This flashcard set covers the classification, clinical manifestations, pathophysiology, diagnostic approach, and management of Adverse Drug Reactions (ADRs) and Drug Eruptions (DEs) based on lecture notes.

Adverse Drug Reactions (ADR)

Any noxious, unintended, and undesired effect of a drug that occurs at doses used in humans for prevention, diagnosis, or treatment (WHO Definition).

Drug Eruptions (DE)

Also known as Adverse Cutaneous Drug Reactions (ACDR); any noxious, unintended, and undesired effect of a drug that has impact on the structure, physiology, or appendices of the skin and mucous membrane, with or without systemic involvement.

SCARs

Severe Cutaneous Adverse Reactions, comprising approximately $6.7\%$ of drug eruption cases.

Type A ADR (Predictable)

Related to known pharmacotoxicological effects and usually dose-dependent; Includes overdosage/toxicity, side effects, secondary/indirect effects, and drug-drug interactions.

Type B ADR (Unpredictable)

Generally dose-independent and unrelated to pharmacologic actions; Includes idiosyncratic reactions, immune-mediated drug allergies, and non-immune mediated pseudoallergies.

Drug Allergy characteristics

An immune-mediated hypersensitivity characterized by a latent period after initial exposure, clinical manifestations different from pharmacological effects, improvement upon drug cessation, and recurrence upon re-exposure.

Type I Hypersensitivity

Immediate-type IgE-mediated reaction where protein-drug complexes cross-link IgE on mast cells and basophils, leading to the release of histamine and leukotrienes.

Type IV Hypersensitivity

Delayed-type T-cell mediated reaction where drugs bound to TCR induce cytokine release and inflammatory reactions, typically with an onset of $2-7$ weeks.

Exanthematous eruption

The most common drug eruption ($\sim 95\%$), manifesting as symmetric, bilateral erythematous macules and papules on the trunk and extremities (type IV HS).

Urticaria

The second most common DE, characterized by rapid-onset itchy wheals (hives) that last $1$ to $24$ hours; mediated by type I immediate hypersensitivity.

Angioedema

Swelling of the deeper dermis and subcutaneous tissue, frequently affecting the lips and periorbital area; can last up to $72$ hours.

Fixed drug eruption (FDE)

A drug eruption characterized by well-demarcated round/oval red macules that recur at the exact same site (localized) upon repeated administration of the causative drug.

Anaphylaxis

An extreme form of acute IgE-mediated systemic reaction involving symptoms like palpitations, shortness of breath, generalized urticaria, and hypotension/shock.

Stevens-Johnson Syndrome (SJS)

A life-threatening mucocutaneous reaction involving skin detachment of less than $10\%$ of the Body Surface Area (BSA) and at least two mucous membranes.

Toxic Epidermal Necrolysis (TEN)

A severe SCAR characterized by skin detachment involving more than $30\%$ of the Body Surface Area (BSA).

Nikolsky sign

A physical exam finding where manual pressure on the skin causes the epidermis to detach from the underlying layers, commonly positive in SJS/TEN.

SCORTEN

A Severity-of-Illness scoring system used specifically to evaluate the severity and predict mortality in patients with TEN.

DRESS

Drug Reaction with Eosinophilia and Systemic Symptoms; a severe reaction with a long latency ($2-6$ weeks) characterized by fever, facial edema (hallmark), lymphadenopathy, and internal organ involvement (e.g., liver).

RegiSCAR

The scoring system and diagnostic criteria used specifically for DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms).

AGEP

Acute Generalized Exanthematous Pustulosis; characterized by the rapid development of numerous small, non-follicular sterile pustules on an edematous erythematous base, often starting in intertriginous areas.

Prick test

A diagnostic test used to identify immediate hypersensitivity reactions, such as drug-induced urticaria.

Patch test

A diagnostic test used to identify delayed-type hypersensitivity reactions (Type IV), such as exanthematous eruptions or fixed drug eruptions.