OIA2004 PHARMACOLOGY OF ALLERGIC RHINITIS

Seasonal Allergic Rhinitis

"Hay fever" — triggered by outdoor allergens (e.g. pollens) during specific seasons.

Perennial Allergic Rhinitis

Year-round symptoms triggered by indoor allergens (dust mites, mold, pet dander).

Common Nasal Symptoms

Sneezing, rhinorrhea, congestion, itching, postnasal drip.

Ocular Symptoms

Watery, itchy, red eyes; periorbital puffiness ("allergic shiners").

Other Symptoms

Throat itch, ear fullness, fatigue, poor concentration.

Triggers of Allergic Rhinitis

Pollens, dust mites, mold, pet dander, seasonal changes.

Cognitive and Daily Functioning

Sleep disturbance, fatigue, reduced academic or work performance.

Ear and Sinus Problems

Otitis media, sinusitis, eustachian tube dysfunction.

Nasal Complications

Nasal polyps, frequent nosebleeds.

Lower Respiratory Impact

Cough, wheezing, asthma exacerbation.

Treatment-related Complications

Rhinitis medicamentosa (from overuse of nasal decongestants), sedating antihistamine side effects.

Key Diagnostic Signs

Sneezing, itchy/watery nose and eyes — especially with known triggers or seasonal pattern.

Seasonal Pattern Clue

Symptoms worsen in dry, warm weather with wind-dispersed allergens (e.g. tree pollen).

Indoor Allergens Clue

House dust mites prevalent in winter due to closed windows.

Misdiagnosis

Often mistaken for recurrent colds.

Histamine H1 Receptor Type

Gq-coupled receptor — found in nasal tissue, bronchial smooth muscle, endothelium, CNS.

H1 Antihistamine Mechanism

Inverse agonists — reduce vascular permeability, itching, and bronchoconstriction.

Histamine Effects

Vasodilation, bronchoconstriction, mucus secretion, itching, AV node suppression.

BBB Penetration (FGAH)

Cross the BBB → sedation, drowsiness, fatigue, cognitive impairment.

Anticholinergic EFFECTS (FGAH)

Useful for motion sickness (e.g. promethazine), but cause dry mouth, urinary retention.

Pediatric Warning (MHRA) (FGAH)

Avoid in children <6 years due to poor risk-benefit profile.

FGAH Contraindications

BPH, angle-closure glaucoma, pyloric stenosis.

Examples of FGAH

Chlorpheniramine, diphenhydramine, promethazine, hydroxyzine, dimenhydrinate.

CNS Penetration (SGAH)

Do not cross BBB → minimal sedation.

Receptor Selectivity (SGAH)

Preferentially target peripheral H1 receptors — good for sneezing and itching.

Not Effective for Nasal Blockage (SGAH)

Mainly relieve sneezing, itching — limited effect on congestion.

Contraindications (SGAH)

Pregnancy and children (except loratadine — better studied).

Examples of SGAH

Loratadine, cetirizine, levocetirizine, fexofenadine, azelastine, desloratadine.

Main Use (Intranasal Corticosteroids)

Primary treatment for nasal blockage — reduce inflammation and eosinophil infiltration.

Onset of Action (Intranasal Corticosteroids)

Takes days to weeks; start before anticipated symptoms (e.g., pollen season).

Technique Matters (Intranasal Corticosteroids)

Correct nasal spray technique improves efficacy and reduces side effects.

Examples of Intranasal Steroids

Beclomethasone, fluticasone, mometasone, fluticasone furoate.

Mechanism (LTRA)

Block leukotriene receptors (LTC4) → reduce eosinophilic inflammation and bronchoconstriction.

Use in Asthmatic Rhinitis (LTRA)

Particularly helpful when allergic rhinitis coexists with asthma.

Examples of LTRAs

Montelukast, zafirlukast, zileuton.

Nasal Decongestants

α-adrenergic agonists (e.g., oxymetazoline, xylometazoline) cause vasoconstriction → reduce congestion.

Oral Decongestants

Pseudoephedrine — longer duration; avoid in hypertension and heart disease.

Rebound Congestion

Prolonged use of nasal decongestants (4–10 days) leads to tachyphylaxis and rhinitis medicamentosa.

Saline Douching Benefits

Flushes mucus/allergens, improves mucociliary clearance, safe for all ages, enhances medication response.

Combination Therapy

Intranasal steroids + antihistamines may be used together for more severe or persistent symptoms.