Pharmacotherapy: Allergic and Pseudoallergic Drug Reactions

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What antibody is involved in a type I allergic reaction?

IgE

IgE binds to these 2 cells

1) Mast Cells
2) Basophils

What happens when the antigen binds the IgE bound to these cells

Causes cells to release cytokines

What are 2 symptoms of a type I allergic reactions

1) Anaphylaxis
2) Urticaria

What are 4 antibiotics that most commonly cause type I allergic reactions

1) Penicillins <<< MAIN ONE
2) Cephalosporin
3) Sulfonamides
4) Vancomycin

What else that isn't an antibiotic most often causes type I allergic reaction

Heparin

What cephalosporins are most cross reactive with penicillins

1st Generation

Type II allergic reactions involves what antibody

IgG

What type of reaction occurs

IgG binds to target hapten or antigen and causes complement destruction of target cells

2 Types of reactions that occur

1) Hemolytic Anemia
2) Thrombocytopenia

4 Drugs that most commonly cause type II allergic reactions

1) Heparin
2) Quinidine
3) Methyldopa
4) Penicillins

Type III allergic reactions involve which 2 antibodies

1) IgG
2) IgM

What happens?

The antibodies bind the antigen or hapten and then form complexes which get deposited in vessel walls and activate complement resulting in vasculitis (excess of antibody and little antigen)

How long does it normally take for type III symptoms to slow

1-2 weeks

What 3 things occur

1) Serum Sickness
2) Vasculitis
3) Lupus

4 Agents that cause type III allergic reactions

1) Penicillins
2) Sulfonamides
3) Radiocontrast Agents
4) Phenytoin

How can we prevent this with radiocontrast agents

Premedicate with prednisone or benadryl

What is involved in a type IV reaction

NO ANTIBODIES, only T cells

Type IV is aka a

Delayed Reaction

What is an immediate hypersensitivity reaction

Type I

Type IV reaction symptoms

Itchty flakey skin reactions / contact dermatitis

What are 3 things that cause these

1) B-Lactams
2) Sulfonamides
3) Phenytoin

Pseudoallergic Reactions do not involve

THE IMMUNE SYSTEM

What is an allergic reaction involving the skin that is very serious? What does it progress to1

SJS progresses to TEN

A patient experiencing anaphylaxis should be observed for at least

12 hours

Treatment of anaphylaxis

1) Epinephrine IM or SQ q 5 minutes / NS infusion
2) If not responding then epinephrine infusion
3) +/- diphenhydramine ; Ranitidine ; Inhaled B-agonist ; dopamine (hypotension refractory to NS and epinephrine) ; hydrocortisone

What is percutaneous (prick) skin testing

They put a drop on the skin and take a needle through the drop and measure allergic response

What is intradermal skin testing

Actually inject antigen into the skin

Cephalosporin / Penicillin Cross Sensitivity

~4% or less ; more common cross-reactivity with 1st generation cephalosporins

Describe carbapenems

ARE CROSS REACTIVE with penicillins

Describe monobactams

Not corss reactive with any beta lactam except ceftazidime

What 2 agents most commonly cause SJS and TEN

1) Sulfonamides
2) Anticonvulsants

What is the main reaction we see with aspirin?

AERD (aspirin-exacerbated respiratory disease)

ASA / NSAIDs can also cause? How often do ASA / NSAIDs cause anaphylaxis

1) Urticaria (most common IgE reaction)
2) Second only to beta-lactams

Opiate reactions are

Pseudoallergic reactions

Why?

These agents cause histamine release

How can we help patients on opidates

Pretreat with antihistamines

What chemotherapy agents cause allergic reactions?

Any of them

One of the only agents that doesn't need to form a complex to cause allergic reaction

Inuslin

What can cause a pseudoallergic reaction if the infusion rate is too high

Vancomycin

You do not attempt desensitization if the patient

Had anaphylaxis to the agnet (anaphylaxis is a contraindication to desensitization)

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