Allergic reactions EXAM 4 Flashcards
What are factors that indicate a true allergy?
-IgE-mediated (allergy caused by the immune system)
-PCN-induced hemolytic anemia
-Contact dermatitis (poison ivy)
-Steven-Johnson’s syndrome
Which reactions are not mediated by IgE but look like a true allergy?
-Vancomycin: Red-person-syndrome
-Morphine-causing urticaria (histamine response, itching)
-Aspirin-induced asthma (bronchoconstriction with bradykinin)
What is the different types of allergic reactions?
Gell Coombs criteria
OBJECTIVE !!
- A: Anaphylaxis (IgE-mediated, immediate hypersensitivity)
- B: Blood cells are involved - Complement-mediated antibody reaction (cytotoxic)
- C: Immune-complex reactions (serum-sickness-like syndrome, lupus) - complexes stuck in the kidney, joints, small vessels
- D: Delayed, dermatology: poison ivy, skin rash
T-cell mediated delayed hypersensitivity (usually dermatologic) example: a rash 3 days after taking Bactrim
Example of Type I and II allergy
Type I: Food allergy (IgE-mediated)
Type 2: hemolytic anemia, Heparin-induced thrombocytopenia (HIT) - blood is involved
What is required to stimulate a Type-1 IgE-mediated allergic reaction?
Prior exposure to the Allergen -> builds antibody memory
so the first time of exposure there is no reaction
What causes the quick response to the allergen in an allergic reaction?
- plasma cells create antibodies after 1st exposure
- the antibodies bind to mast cells
- once the mast cells with the antibodies are exposed to allergens, it release histamines and other chemicals
What is released by mast cells and basophils that causes the hypersensitivity reaction?
What are possible hypersensitivity reactions?
Histamines
Serotonin
Cytokines
Prostaglandins
Leukotrienes
-Urticaria (itching), rhinitis, bronchoconstriction, anaphylaxis
-vasodilation, vascular permeability
-edema, respiratory failure, shock, cardiac collapse
How long after exposure do we expect the hypersensitivity reaction (Type-1) to happen?
- 30 minutes - 2 hours after exposure
- recurrence after 6-8 hours (late-phase reaction)
How do we treat a Type-1 reaction?
STOP the offending agent and list as a true allergy
-Epinephrine 0.2-0.5 mg IM or SQ q5min PRN
-Steroids to reduce the risk of late-phase reaction
supportive:
-Antihistamines, albuterol (ashtma), H2 blockers
-may need IV fluids to maintain BP/CO
-may need vasopressor (norepinephrine)
What are the consequences of Type-II reactions?
Which labs may be affected?
blood dyscrasia: thrombocytopenia, leukopenia, anemia
Cytotoxic reaction
-allergen binds to a host cell and is recognized by an antibody -> phagocytosis or complement-mediated
Which Immunoglobulins are involved in a Type-2 allergic reaction?
IgG and IgM
Which drugs can induce a Type-II allergic reaction?
Penicillins
quinidine
Heparin (HIT)
methyldopa
sulfa drugs (hemolytic anemia, Bactrim-induced hemolytic anemia of newborn)
occurs >72h after exposure
What is a common example of a Type-III allergic reaction?
Serum-sickness syndrome
-fever, malaise, lymphadenopathy, arthralgias, urticaria, morbilliform skin reaction
Which drugs can cause Type-III allergic reactions?
Penicillins
sulfonamides
minoclyclines
hydantoins (phenytoin)
usually develops >72h after exposure, serum-sickness occurs after 7-14 days
Which cells cause a Type-4 allergic reaction?
What are examples?
T-cells
dermatologic:
-contact dermatitis (poison ivy)
-maculopapular exanthemas
-bullous exanthemas
-eczema
Which drugs are most likely to cause a Type-4 allergic reaction?
PCN
sulfa drugs
usually >72h after exposure
What type of rash is common for a drug-induced Type-4 rash?
Maculopapular Rash
Which of the skin reactions are considered serious?
SCARs
SJS
Toxic epidermal necrolysis
Drug Rash with Eosinophilia and Systemic Symptoms
How are Pseudoallergic reactions different from allergic reactions?
Anaphylactoid reactions
they are not mediated by the immune system
What are examples of Pseudoallergic reactions?
-Vancomycin and red-person syndrome (slow infusion rate, pretreat with Tylenol)
-ACE-I and angioedema
-Aspirin-induced asthma
-Ampho B and rigor
Which route of administration bears the greates risk for hypersensitive?
topicals and parental
oral is safest
What are the biggest risk factors for hypersensitivity reactions?
-history of reaction in the past
-concurrent illness (viral infection)
-dose increases
-genetics
-asthma
Which drug can cause any type of allergic reaction (Type 1 to 4)?
ß-lactam
-cross-reactivity with cephalosporin: risk decreases with increasing generation
The risk for Sulfa reaction is increased in which disease?
HIV/AIDS
CAUTION: bc we us Bactrim for PCP prophylaxis and other opportunistic infection in HIV patients
Aspirin and NSAIDs allergy
can be pseudoallergy or real allergy
-> need allergy testing to clarify if they need ASA for stroke
if they are pseudoallergic
-may try to desensitize
How does Drug “Desensitization” work?
usually done in the ICU -> start with a low dose and slightly increase the dose to induce tolerance to the drug
example:
-they really need a PNC, carbapenem, Aspirin
What needs to be done after observing a patient’s allergic reaction?
Document and discuss with the patient and provider
