INTRODUCTION

Allergies occur when the immune system mounts an exaggerated response to harmless substances (allergens) that it mistakenly identifies as threats. The process typically involves two major stages

• Initial Exposure (Sensitization)

An allergen (e.g., pollen, dust mites, pet dander, food) enters the body via inhalation, ingestion, skin contact, or injection. The immune system identifies the allergen as foreign. Antigen-presenting cells (APCs) process the allergen and present it to T-helper cells. T-helper cells (Th2 cells) stimulate B cells to produce immunoglobulin E (IgE) antibodies specific to the allergen. These IgE antibodies bind to receptors on mast cells and basophils, “sensitizing” the immune system for future encounters.

• Subsequent Exposure (Allergic Reaction):

On subsequent exposure, the allergen binds to IgE antibodies on mast cells and basophils. This cross-linking triggers the release of inflammatory mediators like histamine, leukotrienes, and cytokines.

SYMPTOMS OF ALLERGY

Histamine and other mediators exert their effects by binding to specific receptors:

• H1 receptors: Cause pruritus, swelling, sneezing, nasal discharge, watery eyes, and urticaria.
• H2 receptors: Increase gastric acid secretion, though these effects are less common in typical allergic responses.

The symptoms vary depending on the type of allergen and route of exposure—respiratory, dermal, or systemic (as with food or drug reactions).

PREDISPOSING FACTORS.

Key predisposing factors include:

• Genetics: A family history of allergies increases susceptibility.
• Environmental factors: Pollution and early allergen exposure contribute significantly.
• Immune dysregulation: An exaggerated Th2 response increases the risk of hypersensitivity

TREATMENTS

Antihistamines relieve symptoms by competing with histamine for H-receptor binding sites, thereby blocking its effects.

• H1 antihistamines act on H1 receptors to reduce itching, swelling, nasal congestion, and hives.
• H2 antihistamines (e.g., ranitidine, famotidine) target gastric H2 receptors to decrease acid secretion.

Note: Antihistamines do not inhibit histamine production or remove the underlying allergen.

Ashihist is a first-generation H1 antihistamine containing Chlorpheniramine Maleate 10 mg. It blocks H1 receptors, providing rapid relief from histamine-mediated allergic reactions. Owing to its fast onset, wide utility, and reliability in acute allergic presentations, Ashihist serves as an essential injection for veterinary practitioners managing allergy cases.