Allergies

Focus

Summary

Goal of Therapy

Relieve allergic symptoms such as sneezing, runny nose, watery eyes, and itch by blocking histamine action.

Non-Pharmacological Management

• Allergen avoidance (dust, pets, pollen, certain foods)

• Saline nasal sprays

• Air filtration or allergen-proof bedding

Main Pharmacological Classes

Antihistamines (H₁ blockers) — topical/local or oral options

Topical / Local Antihistamines

- Intraocular (eye drops): Treat allergic conjunctivitis (e.g. azelastine, levocabastine)

- Intranasal (sprays): Treat allergic rhinitis (e.g. azelastine, olopatadine)

Oral Antihistamines

Older (Sedating / 1st Gen):

• Dexchlorpheniramine (Polaramine®)

• Promethazine (Phenergan®)

Newer (Less Sedating / 2nd Gen):

• Cetirizine (Zyrtec®)

• Loratadine (Claratyne® / Aerius®)

• Fexofenadine (Telfast®)

Mechanism of Action

Block histamine H₁ receptors → prevent histamine-mediated vasodilation, itch, sneezing, and mucous secretion.

Indications / Use

• Allergic rhinitis

• Urticaria (hives)

• Allergic conjunctivitis

• Pruritus (itching)

Comparative Advantages

- 1st Gen: Also useful for motion sickness or short-term sedation (cross BBB).

- 2nd Gen: Longer-acting, non-sedating, better daytime tolerance.

Common ADRs

- 1st Gen: Drowsiness, dry mouth, blurred vision, urinary retention (anticholinergic).

- 2nd Gen: Headache, mild fatigue (rare).

Counselling Points

- Avoid alcohol or driving with sedating antihistamines.

- Take once daily (usually at night if sedating).

- For eye/nose products: use regularly during allergy season.

High-Yield Suffixes

-ine = Antihistamines (e.g. loratadine, cetirizine, fexofenadine)