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Year 2 > Allergic reactions to drugs and anaphylaxis > Flashcards

Allergic reactions to drugs and anaphylaxis Flashcards

1
Q

What is type I hypersensitivity

A

IgE mediated-drug hypersensitivity

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2
Q

How does type I hypersensitivity relate to acute anaphylaxis

A
  1. Prior exposure to antigen/drug
  2. IgE antibodies formed after exposure to molecule
  3. IgE becomes attached to mast cells or leucocytes, expressed as cell surface receptors
  4. Re-exposure causes mast cell degranulation and release of pharmacologically active substances
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3
Q

How long does anaphylaxis last for

A

1-2 hours

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4
Q

What is anaphylaxis

A
  1. Vasodilation
  2. Increased vascular permeability
  3. Bronchoconstrcition
  4. Urticaria
  5. Angio-oedema
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5
Q

What are type II reactions

A

Drug metabolite combines with a protein and body treats it as a foreign protein, making antibodies against it

Antibodies combine with antigen and complement activation damaged the cell

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6
Q

What are type III reactions

A
  1. Antigen and antibody form large complexes and activate complement
  2. Small blood vessels are damaged or blocked
  3. Leucocytes attracted to the site of reaction release pharmacologically active substances leading to an inflammatory process
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7
Q

Example of type III reactions

A

Glomerulonephritis

Vasculitis

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8
Q

What are type IV reactions

A

Antigen-specific receptors develop on T-lymphocyte

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9
Q

What are non-immune anaphylaxes caused by

A

Direct mast cell degranulation caused by some drugs

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10
Q

What is anaphylactic shock

A

Hypotension

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11
Q

Main features of anaphylaxis

A
  1. Exposure to drug
  2. Rapid
  3. Swelling of lips, face, oedema and central cyanosis
  4. Wheeze
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12
Q

How is anaphylaxis managed

A
  1. ABC
  2. Stop drug if infusion
  3. Adrenaline IM 500mcg (300mcg epi-pen)
  4. High flow oxygen
  5. IV antihistamine
  6. IV Hydrocortison
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13
Q

Example of anti-histamine used when treating anaphylaxis

A

Chlorphenamine (10mg)

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14
Q

How much Hydrocortisone is used

A

100-200 mg

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15
Q

What medicinal factor increases risk for hypersensitivity

A
  1. Protein or polysaccharide-based macro molecules
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16
Q

What host factors contribute to hypersensitivity

A
  1. Females > Males

2. Immunosuppression

17
Q

What genetic factors increase risk of hypersensitivity

A
  1. Certain HLA groups
18
Q

Three drugs that commonly cause anaphylaxis

A

Penicillin
Aspirin
NSAIDs

19
Q

How common are penicillin allergies

A

2%

20
Q

What should we do if we see someone on the street undergoing an anaphylactic reaction s

A 
1. ABCDE
A - airways
B - Breathing
C- Circulation 
D - Disability
E - Exposure
  1. Diagnosis
    Look for: Acute onset of illness
  2. Call for help
  3. Lie patient flat and raise legs
  4. Adrenaline
  5. The other hard stuff
21
Q

Clinical criteria for being ‘allergic’ to a drug

A
  1. Does not correlate with drug properties
  2. No linear relation to dose
  3. Induction period on primary exposure
  4. Disappearance on cessation
  5. Re-appears on re-exposure
  6. Occurs in a minority of patients
22
Q

What cells secrete IgE

A
  1. Eosinophils
  2. Basophils
  3. Mast Cells
23
Q

Why do we need basophils when we have mast cells

A

Mast cells can only reside in tissues - cannot circulate

24
Q

What does mast cell require for division

A

CD117 (c-kit)

25
Q

What makes an allergen

A
  1. Presence of PAMPs
26
Q

Clinical presentation of Anaphylaxis

A
  1. ABCDE
  2. Elevated serum tryptase and histamine levels
  3. Vasodilation, flushing and lower BP
  4. Bronchial SM contraction (SOB)
  5. Skin Rash and swelling (mastocytosis)
  6. Urticaria
  7. Angio-oedema

Takes 1-2 hours

EVENTUALLY: Pain and vomiting

27
Q

Treatment of allergic reactions

A
  1. Increase dose of antigen (sub lingually) - ectopic eczema (not asthma)
  2. Stop IgE production:
    IL-4 antagonist (Pitakinra)
    Lumiliximab (CD23 antibodies) - leukaemia
    ————————-
    Anti-IgE therapy in atopic individuals:
    Omalizumab inhibits binding of IgE to receptor on mast cells

Anti-cytokine antibodies:
Infliximab
IL-5 antibody (Mepolizumab) - asthma

Mast Cell inhibitors:

  1. Sodium Cromoglycate (mast cell stabilisers, reduces mediator release)
  2. Salmeterol
  3. Prednisololne
  4. MAP kinase inhibitors
  5. Calcium channel blockers
Finally:
H1 antagonists
Montelukast - leucotrienes
Trypatase Inhibitors 
PAR-2 antagonists
28
Q

treatment of anaphylaxis

A
  1. 0.15mg/0.3mg IM adrenaline

Beta-2:
Causes bronchodilaition
Myocardial contraction
Inhibition of mast cells

Alpha-1:

  1. Peripheral vasoconstriction
  2. Reduces oedema

High Flow Oxygen
IV Fluids
Antihistamine (Chlorphenamine 10mg)
IV Hydrocortisone (100-200mg)

29
Q

What is non-immune anaphylaxis

A
  1. Due to direct mast cell degranulation
30
Q

What is anaphylactic shock

A

Hypotension

Year 2 (155 decks)

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