Classification of antihistamine

Below we have described the classification of antihistamine based on receptor type and generation with their roles in allergy relief and related conditions.

Classification of antihistamine:

• The medications listed can be classified into three main categories: H1-antagonists (antihistamines), H2-antagonists (histamine H2 receptor blockers), and gastric proton-pump inhibitors (PPIs).
• Below is a proper classification of each:

1. H1-Antagonists (Antihistamines):

   • These are drugs that block the H1 histamine receptor, often used to treat allergic reactions, motion sickness, and as sedatives.

     1. First-Generation H1-Antagonists:

        • Diphenhydramine hydrochloride
        • Dimenhydrinate
        • Doxylamine succinate
        • Clemastine fumarate
        • Diphenylpyraline hydrochloride
        • Triphelenamine hydrochloride
        • Chlorcyclizine hydrochloride
        • Meclizine hydrochloride
        • Buclizine hydrochloride
        • Chlorpheniramine maleate
        • Triprolidine hydrochloride*
        • Phenidamine tartrate
        • Promethazine hydrochloride*
        • Trimeprazine tartrate
        • Cyproheptadine hydrochloride
        • Azatidine maleate

     2. Second-Generation H1-Antagonists:

        • Astemizole (discontinued in some regions due to safety concerns)
        • Loratadine
        • Cetirizine
        • Levocetirizine

     3. Mast Cell Stabilizer:

        • Cromolyn sodium (although not a true H1-antagonist, it stabilizes mast cells to prevent histamine release and is often grouped with antihistamines for allergic treatment)

2. H2-Antagonists (Histamine H2 Receptor Blockers):

   • These drugs block the H2 histamine receptor, reducing stomach acid production, often used in the treatment of ulcers and gastroesophageal reflux disease (GERD).
     • Cimetidine
     • Famotidine
     • Ranitidine* (discontinued or restricted in many regions due to safety concerns)

3. Gastric Proton-Pump Inhibitors (PPIs):

   • These inhibit the proton pump in the stomach, reducing acid secretion, commonly used for GERD, peptic ulcers, and other acid-related disorders.
     • Omeprazole
     • Lansoprazole
     • Rabeprazole
     • Pantoprazole

This classification separates the drugs based on their mechanism of action and therapeutic use.

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