Summarizing of Histamine action and H1-and H2-antagonist (H1-and H2-antihistamine drugs).

                  Antihistamine and H1-and H2-antagonist

Histamine is a physiological active, endogenous substance (autocoid) that is produced in the
body by decarboxylation of amino acid, histamine and stored in mass cells and basophils where
it is protected from ubiquitous destructive enzymes (histaminases). It binds to and actives
histamine H1- and H2-receptors in various sites in the body. H3-receptors were described and may
be involved in the control of histamine synthesis. H1- and H2-receptors: direct and indirect microvascular dilatation. H1-receptors: increased vascular permeability. H1-receptors activation: nose, eyes, respiratory tract, and skin allergy signs and symptoms. H2-receptors activation: stimulates gastric acid secretion.

 List of H1 antihistamine (H1-antagonists)

1) Highly sedative

- Diphenhydramine 25-50mg oral
- Dimenhydrinate 25-50mg oral
 - Promethazine 25-50mg oral, i.m (1mg/kg)
- Hydroxine 25-50mg oral

2) Moderately sedative

- Pheniramine 20-50mg oral, i.m
- Cyproheptadine 4mg oral
 - Meclozine (Meclizine) 25-50mg oral
- Cinnarazine 25-50mg oral

3) Mild sedative

- Chlorpheniramine 2-4mg (0.1mg/kg), oral, i.m
- Dexchlorpheniramine 2mg oral
 - Triprolidine 2.5-5mg oral
 - Clemastine 1-2mg oral

Second line of H1 antihistaminics

- Fexofenadine 120-180mg oral
- Loratadine 10mg oral
- Desloratadine 5mg oral
- Cetirizine 10mg oral
 - Levocetirizine 5-10mg oral
 - Azelastine 4mg oral, 0.28mg intranasal
- Mizolastine 10mg oral
- Ebastine 10mg oral
- Rupatadine 10mg oral
- Terfenadine : discontinued
- Astemizole : discontinued

List of H2 antihistamine (H2-antagonists)

- Burimamide i.v
- Metiamide oral, i.v : discontinued
- Cimetidine 200mg oral - Ranitidine 30mg oral - Femotidine
- Nizatidine 75mg