L19 Drugs In Allergy And Anaphylaxis

Question 1

What are the types Of drugs used to treat type 1 hypersensitivity

Answer 1

Controlling agents: modest or moderate drugs used to stop actions of prevailing mediators being released
Relieving agents: acute to moderate to severe used to physiologically antagonize manifestation +_ controlling agents
Supportive management: procedures+_ agents that support any existing respiratory or circulatory collapse and must be immediately initiated

Question 2

What does histamine do

Answer 2

Imp mediator of an allergy
Causes inflammation by stimulation of H1 receptors and induces vasodilation and inc capillary permeability and stimulates sensory nerve endings to produce itching, pain

Mainly by mast cells especially in skin GIT and respiratory tract

Question 3

What is histamine suppressed by

Answer 3

Inhibition of mast cell degranulation by: cromolyn Na and ketotifen (mast cell stabilizers)

Completely blocking H1 receptors by antihistamines:
Diphenhydramine
Loratadine
Fexofenadine

Question 4

What are leukotrienes

Answer 4

Produced from arachidonic acid in phospholipid of cell membrane by action of lipoxygenase enzyme
Mainly released in inflammatory and allergic reactions causing excessive mucus production and bronchoconstriction

Question 5

How are leukotrienes suppressed

Answer 5

Inhibiting their synthesis: 5 lipoxygenase inhibitors : zileuton
Blocking their receptors: leukotriene receptor antagonists: montelukast
Suppress gene expression of most mediators: steroids: prednisone
Bind IgE: by using omalizumb (MAB)

Question 6

How can physiological antagonism occur

Answer 6

Adrenergic agonist: epinephrine
Can be repeated every 5 to 10 min till manifestations decrease
Patient must be observed for 4-6 hours to make sure they don’t develop biphasic anaphylaxis

Question 7

What are the relievers of bronchoconstriction

Answer 7

B2 adrenergic agonists: salbutamol

Question 8

How can refractory hypotension by corrected

Answer 8

By using adrenergic agonist dopamine

Only if hypotension still exists despite intake of adrenaline

Question 9

What supportive management can be done

Answer 9

Respiratory support: opening airway in cases of laryngeal edema
Circulatory support: positioning head down legs up

Question 10

First generation names of antihistamine

Answer 10

Chlorpheniramine

Diphenhydramine

Question 11

2nd generation antihistamine names

Answer 11

Loratadine

Cetrtizine

Question 12

3rd generation of antihistamine names

Answer 12

Levocetrizine

Fexofenadine

Question 13

Mechanism of action of all generations antihistamine

Answer 13

First:Block h1
Anti ach m1
a-ADR and 5HT 2a/c
Ion channel modulation
2nd and third: block only H1

Question 14

Kinetic properties of all generations

Answer 14

First: cross BBB/lipophillic
Short duration
Interact with hepatic metabolizing enzymes

Second: poorly crossing/hydrophilic
Longer duration
No interaction

Third: no crossing
Longer duration
No interaction

Question 15

Dynamic properties of all generations

Answer 15

First: non selective sedating
Antihistamine with antiemetic +_ hypotensive actions

Second and third: selective non sedating
Anti allergic with no other actions

Question 16

Why are antihistamines used in allergic disorders and why not

Answer 16

They have good control im case of rhinitis conjunctivitis urticaria and flue when histamine is main mediator

Poor control in cases of otitis, atopic dermatitis, asthma,anaphylaxis where other mediators also interplay

Question 17

Why would antihistamines be used in other disorders

Answer 17

Only 1st generation
Off label treatment of insomnia
Nausea,vomiting via its potent antiemetic anticholinergic action
Motion sickness and vertigo by reducing stimulation of inner ear
Off label appetite enhancer through its antagonistic action on specific serotonin receptor

Question 18

Side effects of 1st generation antihistamines

Answer 18

Sedative
Anticholinergic: dry mouth, urinary retention, inc intraocular pressure
a-ADR effects as postural hypertension,dizziness and reflex tachycardia

Question 19

Side effects of 2nd generation

Answer 19

Induce arrhythmias especially in overdose due to prolonged cardiac action Potential secondary to blockade of K+ channels during repolarization