Allergy

Question 1

What immunoglobulin does Type 1 hypersensitivity rely on

Answer 1

IgE antibody

Question 2

What type of reactions are allergic reactions

Answer 2

Type 1 hypersensitivity and IgE-mediated

Question 3

How does allergic reaction (Type 1 Hypersensitivity) occur?

Answer 3

IgE binds to Fc receptors on mast cells

Allergen crosslinks with IgE + basophils + eosinophils

This causes entry of Ca^{<strong>2+</strong>} ions

Mast cells undergo degranulation (of histamine) + release of inflammation mediators to cause:

• permeability
• chemotaxis
• mucus
• oedema

Question 4

What is allergic rhinitis?

Answer 4

Inflammation of the inside of the nose caused by an allergen

Question 5

What type of allergens trigger rhinitis

Answer 5

Perennial = house dust mite + animal hair/FUR

Seasonal = hay fever - pollen

Occupational = latex

Associated with atopy (genetic predisposition)

Question 6

Signs + symptoms of allergic rhinitis

Answer 6

Nasal itching

Sneezing

Rhinorrhoea - runny nose

Conjunctival - itchy red eye (worsened by irritants)

Question 7

What is the no.1 mediator from mast cells + basophils

Answer 7

Histamine - acts on H₁ receptors

Question 8

How can we manage allergic rhinitis?

Answer 8

Avoid pollen in spring by staying indoors or wearing glasses

Avoid dust mites by:

• vacuuming
• wooden floors over carpets
• wash bed clothes @ 60 degrees
• freeze pillows

Question 9

What are anti-histamines?

Answer 9

A drug that treats allergic rhinitis

It removes rhinorrhoea, itching, conjunctivitis + sneezing but not nasal obstruction

Act as H₁ antagonist

Penetrate BBB (blood-brain barrier)

Have anti-muscarinic effects (promethazine)

Not ideal, effects of alcohol enhanced

Question 10

Examples of sedating anti-histamines

Answer 10

Chlorphenamine e.g. piriton (or syrup for children over 1 year)

Alimenazine* e.g. trimeprazine

Promethazine* e.g. phenergen

* = more so

Question 11

Examples of non-sedating anti-histamines

Answer 11

Loratadine (clarityn) - 1st CHOICE

Acrivastine (benadryl) - have to be taken tds (not ods)

Cetrizine (zirtek)

Fexofenadine (telfast) - POM

Question 12

Name a topical ‘nasal’ anti-histamine

Answer 12

Azelastine (rhinolast)

Rapid onset

Effective but not for eye symptoms

Azelastine in eye drop formulation for allergic conjunctivitis = rapid relief

Also lodoxamine as eye drops

Question 13

Examples of intranasal corticosteroids

Answer 13

Beclometasone

Budesonide

Fluticasone

Triamcinolone

Anti-inflammatory = Reduce cytokines and chemokines which reduce recruitment of immune cells in epithelial mucosa

Question 14

What are cromones?

Answer 14

Mast cell stabiliser - Inhibits mast cell degranulation

e.g. sodium cromoglicate + medocromil sodium

Nasal + eye

Weak effect

Many side effects

Used for seasonal disease

Up to 4-6 times daily

Eye drops - most effective for conjunctival symptoms

Question 15

Example of leukotriene receptor antagonist

Answer 15

Montelukast

Less effective than nasal steroids

Licensed for seasonal allergic rhinitis with asthma

Question 16

What is nasal congestion?

Answer 16

Blocked or stuffy nose

e.g. allergic rhinitis or common cold

Excess mucus production

Histamine causes increased blood flow leading to nasal tissue swelling (oedema) which is caused by:

• colds, rhinitis, sinusitis

Decongestants cause nasal vasoconstriction to reduce nasal tissue swelling + mucus flow

alpha₁ adrenoceptors cause vasoconstriction

Question 17

What are decongestants?

Answer 17

Symptomatic relief - reduce feeling of congestion

Both topical + systemic decongestants act on alpha-adrenoceptors

Topical ‘nasal’ treatment:

• phenylepherine (alpha₁)
• xylometazoline/oxymetazoline (alpha₂)

Alpha-adrenoceptor agonist cause vasoconstriction

Reverse vasodilatation

Reduce flow of mucus

Act locally

Rebound congestion - use for < 7 days

Question 18

What are systemic decongestants?

Answer 18

e.g. phenylepherine (alpha₁-adrenoceptor = selective)

Question 19

What is hyposensitisation?

Answer 19

Desensitisation towards an allergen

Could be effective for hayfever - when allergen is identified _ conventional treatment has failed

Appropriate for wasp + bee venom sting

Question 20

What is Grazax?

Answer 20

Grazax® contains a grass pollen allergen.

By taking many small doses of Grazax you are able to build up a tolerance to grass pollen. This reduces the symptoms of your allergic reaction.

Take 4 months before pollen season and then daily

Uncertain if effective

Question 21

What is anaphylaxis?

Answer 21

A serious, life-threatening allergic reaction

Can cause more than one of the following:

• angioedema = swelling of lower skin
• wheezing
• itching
• hypotension

Question 22

What is the treatment for anaphylaxis?

Answer 22

Oxygen

Adrenaline - increase CO₂ + bronchodilation

Salbutamol = wheezing

Chlorphenamine (antihistamine) - IV/IM

Hydrocortisone - IV

Shock boxes

EpiPens

Medic alert bracelet

Question 23

What are the MHRA guideline on people who carry epipens?

Answer 23

People who have been prescribed an adrenaline auto-injector because of the risk of anaphylaxis should carry two with them at all times for emergency, on-the-spot use. After every use of an adrenaline auto-injector, an ambulance should be called (even if symptoms are improving), the individual should lie down with their legs raised and, if at all possible, should not be left alone