AUTO - B. TREATMENT OF ALLERGY-COVERED Flashcards
what is an allergy
- the antigen is the allergen
- causes IgE synthesis
- IgE (of antibody) attaches to mast cell surface
- cross-linking of IgE by allergen allowed calcium entry
- mast cell degranulation, release of mediators of inflammation:
permeability of blood vessels hence leakiness hence oedema (due to increased blood flow)
chemotaxis
mucus production in airways
phase 1 of developing an allergy (don’t need to know details)
Induction phase - sensitisation
- allergen captured by APCs
- presents part of allergen (epitope) to T-cells
- specific T-cells produce IL-4, IL-5, IL-13
- stimulates B-cells to produce IgE antibodies
- IgE antibodies bind to basophils and mast cells
*later exposure - already have IgE bound to mast cells and hence allergen binds directly to mast cells and causes degranulation
phase 2 of developing an allergy
Reactive phase - subsequent exposure to allergen
- cross-linking of antibodies
- degranulation
- release of histamine (acts on H1 receptors), LT, prostaglandins, chemotactic factors
consequences of degranulation
- vasodilation/oedema (hives)
- bronchoconstriction (asthma)
- mucus production (rhinitis)
common allergens
- house dust mites (faeces)
- pollen
- animal fur
- moulds
- food
allergic rhinitis
- nasal itching
- inflam of nasal passages
- sneezing
- rhinorrhoea
- can cause conjunctivitis: itchy bilateral red eyes
management of rhinitis
- avoid pollen, stay indoors, glasses
- vacuum house
- wooden floors vs carpets
- wash bed clothes at 60
- freeze pillows
1st choice for rhinitis: antihistamines
- H1 antagonists removes rhinorrhoea, itching, conjunctivitis, sneezing
- DON’T remove nasal obstruction (different receptor subtype)
- histamine receptors in brain
- penetrate BBB so antagonise alertness - sleepiness
- avoid alcohol as sedative effects of alcohol enhanced
Sedating
- Chlorphenamine (Piriton) if >1, syrup
- Alimenazine: more sedating
- Promethazine: more sedating
Non-sedating:
- Acrivastine
- Cetirizine
- Fexofenadine (POM)
- Loratadine (>2) - 1st choice
All daily except Acrivastine (3x)
1 hour onset
Topical nasal antihistamines
- Azelastine (Rhinolast) - spray
- rapid onset (15 minutes)
- 2-4x day
- not for eye symptoms
- Azelastine eye drops in allergic conjunctivitis provide rapid relief (nasal + eye symptoms = oral tablet)
- Lodoxamine eye drops
Intranasal corticosteroids (for more severe allergy)
- Beclometasone (Beconase)
- Budesonide (Rhinocort)
- Fluticasone
- Trimcinolone
- rhinitis and conjunctivitis
- 12 hours onset
- 1x daily
children need prescription - Anti-inflam: reduce cytokines and chemokines and reduce recruitment of immune cells in epithelial mucosa
Counselling on corticosteroids
- days/weeks for max effect due to changes in gene transcription (preventer)
- use oral antihistamine in meantime
- start week or 2 before hay fever season
- nasal so low risk of hypothalamic pituitary adrenal axis suppression
- but still monitor child’s height
- can use in addition to inhaled steroids if asthmatic due to localised delivery
- oral steroids - not first line but can be used for <2 weeks in severe disease
Cromones
- Sodium cromoglicate and nedocromil sodium
- nasal and eye (OTC - Opticron)
- mast cell stabiliser - inhibits degranulation
- for seasonal disease
- 4-6x daily
Leukotriene receptor antagonists
- Montelukast
- less effective than nasal steroids
- seasonal allergic rhinitis with asthma
- excellent control with antihistamine
Nasal congestion (obstruction)
- blocked/stuffy nose
- allergic rhinitis/sinusitis/cold?
- excess mucus production
- histamine causes increased blood flow which leads to oedema which is the feeling of congestion
- decongestants cause nasal vasoconstriction to reduce tissue swelling and mucus flow
- alpha-ARs cause vasoconstriction
Decongestants
- Xylometazoline: alpha2-AR selective
- Phenylephrine: alpha1-AR selective
- vasoconstriction and prevent oedema
- reduce mucus flow
- local action
use for more than 7 days: rebound congestion
- fatigue of smooth muscle due to constriction of blood vessels for long time and lose effectiveness or
- desensitisation of receptors
