L22 Seasonal respiratory allergies

Allergic Rhinitis is hay fever, caused by seasonal allergens like [blank_start]pollen and grasses[blank_end], and perennial allergens like [blank_start]animal dander, mould, and dust mites[blank_end]. Common symptoms include a runny, stuffy [blank_start]nose[blank_end], sneezing, cough, wheezing, and itchy, red, watery [blank_start]eyes[blank_end].

The pathology of hay fever has 2 key stages, [blank_start]sensitisation[blank_end] and re-exposure causing inflammation. Upon re-exposure to an allergen, [blank_start]mast[blank_end] cells in the nasal [blank_start]mucosa[blank_end] primed with IgE antibodies release [blank_start]histamines[blank_end], leukotrienes, and prostaglandins. [blank_start]Cytokines[blank_end] cause the infiltration of lots of [blank_start]activated[blank_end] immune cells. These release mediators. The blood vessels become more porous, [blank_start]dilating[blank_end] and emptying easier. Histamines bind to blood vessels, [blank_start]goblet[blank_end] cells and nerves.

Early-phase symptoms (minutes): - [blank_start]sneezing[blank_end] - nasal [blank_start]itching[blank_end] and congestion - rhinorrhoea ([blank_start]runny[blank_end] nose) Late-phase symptoms (6-12 hr): - nasal [blank_start]congestion/obstruction[blank_end] - nasal hyperactivity

Therapy options for allergic rhinitis are drugs for symptomatic relief, and to avoid triggers. Dosage forms are: • [blank_start]Oral[blank_end] tablets • [blank_start]Intranasal[blank_end] sprays • [blank_start]Eye[blank_end] drops Drugs can: - Prevent release ([blank_start]Mast cell stabilisers[blank_end]) - Prevent inflammation ([blank_start]Corticosteroids[blank_end]) - Block action ([blank_start]Antihistamines and anticholinergics[blank_end])

H1 antihistamines are [blank_start]inverse agonists[blank_end] and not receptor antagonists. Therefore they have no effect on histamine [blank_start]release[blank_end] from storage [blank_start]sites[blank_end] and are more effective if given [blank_start]before[blank_end] histamine release occurs. H1 antihistamines can decrease the itch, decrease vascular [blank_start]permeability and dilation[blank_end], decrease [blank_start]antigen[blank_end] presentation and pro-inflammatory cytokines, increase mast cell [blank_start]stability[blank_end] and decrease [blank_start]mediator[blank_end] release.

First generation H1 antihistamines have low [blank_start]H1[blank_end] selectivity and high [blank_start]BBB[blank_end] permeability. They take [blank_start]2-3[blank_end] hours to onset of action, and last [blank_start]12-24[blank_end] hours. They are taken [blank_start]tid or qid[blank_end]. Their side effects can include sedation, dry [blank_start]mouth[blank_end], urinary [blank_start]retention[blank_end], increased appetite, postural [blank_start]hypotension[blank_end] or dizziness, and possibly ventricular arrythmias. Second generation antihistamines have [blank_start]high[blank_end] H1 selectivity and [blank_start]low[blank_end] BBB permeability, therefore side effects are uncommon. They take [blank_start]1-2[blank_end] hours to onset of action, and the majority of them are dosed [blank_start]once[blank_end] daily, lasting for 24 hours.

Corticosteroid nasal sprays act primarily during the [blank_start]late[blank_end] phase and are good for [blank_start]long[blank_end] term management. For allergic rhinitis there is no linear association between glucocorticoid [blank_start]potency[blank_end] and clinical [blank_start]response[blank_end], meaning we can use a low potency glucocorticoid effectively. Since it is intranasally sprayed, systemic absorption would be negligible and would be expected to pose [blank_start]fewer[blank_end] side effects. But those are: • Dryness, stinging, burning, and [blank_start]epistaxis[blank_end] • Nasal mucosal atrophy, with [blank_start]chronic[blank_end] topical steroid use

Intranasal decongestants are [blank_start]sympathomimetic[blank_end] drugs like xylometazoline & oxymetazoline. They have a [blank_start]rapid[blank_end] onset of action though are used [blank_start]short[blank_end] duration, as you risk [blank_start]rebound[blank_end] congestion. The drugs act on [blank_start]alpha adrenoreceptors[blank_end] in the nasal blood vessels, fixing [blank_start]rhinorrhoea and/or sneezing[blank_end], but not congestion.