Hypersensitivity Reactions and Pharmacology

Vocabulary flashcards covering key terms, hypersensitivity types (1-4), nonimmune reactions, adverse drug reactions, and pharmacological treatments based on the lecture.

Pruritus

A medical term defined as itching.

Urticaria

A raised, red, itchy rash that can occur anywhere on the body, commonly referred to by slang terms such as hives, wheels, or welts.

Angioedema

Tissue swelling in the face, lips, and tongue caused when fluid leaks out of blood vessels, which can lead to airway obstruction.

Anaphylaxis

An exaggerated response to an allergen characterized by massive vasodilation, dropping blood pressure, inadequate oxygen delivery to tissues, shock, organ failure, and potential death.

Adverse Drug Reaction (ADR)

A non-preventable event that occurs when a medication is taken as directed, caused by the mechanism of action of the drug.

Drug Hypersensitivity Reaction

An adverse drug reaction that resembles an allergic reaction, but where complete immune system involvement is unknown.

Drug Allergy

An adverse reaction known to be caused specifically by an immune response, rather than the mechanism of action of the drug.

Type A Adverse Drug Reaction

A dose-related adverse drug reaction caused by the mechanism of action of the drug, such as sedation from opioid pain medications.

Type B Adverse Drug Reaction

A non-dose-related, "bizarre" adverse drug reaction that is not due to the mechanism of action of the drug, encompassing hypersensitivity reactions and allergies.

Vancomycin Infusion Reaction

A nonimmune hypersensitivity reaction occurring when IV vancomycin is administered too quickly, causing the body to turn bright red; treated by slowing the infusion rate.

ACE-Induced Cough and Angioedema

A nonimmune hypersensitivity reaction caused by increased bradykinin levels due to inhibition of the ACE enzyme.

Opioid-Induced Histamine Release

A nonimmune reaction where opioid medications cause mast cells to directly release histamine, resulting in itching and flushing.

Type 1 Hypersensitivity

An immediate, anaphylactic response mediated primarily by IgE antibodies binding to mast cells and basophils to release histamine, leading to vasodilation, increased vascular permeability, fluid leakage, mucus secretion, and bronchial muscle spasms.

Hygiene Hypothesis

The hypothesis stating that a lack of exposure to antigens and microbes during childhood increases the likelihood of getting sick and developing allergies later in life.

Type 2 Hypersensitivity

An antibody-mediated "friendly fire" reaction where the body recognizes part of itself as foreign and launches complement activation, antibody-dependent cellular cytotoxicity, or opsonization against target cells.

Complement Activation

A mechanism in Type 2 hypersensitivity where IgG and IgM antibodies bind to target cells to form the membrane attack complex and kill target cells directly.

Antibody-Dependent Cellular Cytotoxicity (ADCC)

A Type 2 hypersensitivity mechanism where target-cell-bound antibodies are recognized by NK cells and macrophages, which release perforin and granzymes to cause target cell death.

Opsonization

The tagging of a target cell by an antibody so that it can be engulfed and cleared by a phagocyte.

Goodpasture Syndrome

A clinical example of Type 2 hypersensitivity that targets the basement membranes in the kidneys and lungs.

Type 3 Hypersensitivity

An immune complex-mediated reaction where circulating antigen-antibody complexes (mainly IgG or IgM) deposit in blood vessel walls, kidney glomeruli, joints, and skin when phagocytes cannot clear them.

Serum Sickness

A Type 3 hypersensitivity reaction occurring approximately $7$ to $14$\,days after exposure to proteins in antivenom, causing fever, urticarial rash, lymphadenopathy, and glomerulonephritis.

Arthus Reaction

A localized Type 3 hypersensitivity reaction occurring at the injection site in a previously sensitized individual, such as after receiving a Tdap booster given every $10$\,years.

Type 4 Hypersensitivity

A cell-mediated, delayed-type hypersensitivity reaction driven by T cells rather than antibodies, divided into a sensitization phase and an effector phase.

Perforin

A molecule released by cytotoxic T cells in Type 4 hypersensitivity reactions that pokes holes in the target cell membrane.

Granzyme

A molecule released by cytotoxic T cells in Type 4 hypersensitivity reactions that initiates apoptosis in target cells.

Allergic Contact Dermatitis

A Type 4 delayed hypersensitivity reaction to triggers like poison ivy, nickel, latex, or cosmetics, resulting in an itchy, red, blistery rash.

Epinephrine

The first-line therapy for anaphylaxis that acts by increasing heart rate, inducing vasoconstriction to raise blood pressure, and causing bronchodilation.

First-Generation Antihistamines

Antihistamine agents (such as Benadryl) that easily cross the blood-brain barrier, causing central nervous system sedation as well as antimuscarinic side effects.

Second-Generation Antihistamines

Antihistamine medications (such as Claritin, Zyrtec, and Allegra) that are less likely to cross the blood-brain barrier and cause less sedation compared to first-generation antihistamines.

Antimuscarinic Side Effects

Side effects caused by first-generation antihistamines summarized as "can't see, can't spit, can't eat, can't poop," consisting of blurry vision, dry mouth, urinary retention, and constipation.