H1-antihistamines H1-antihistamines refer to compounds that inhibit the activity of the
H1 receptor. Clinically, H1-antihistamines are used to treat
allergic reactions and
mast cell-related disorders.
Sedation is a common side effect of H1-antihistamines that readily cross the
blood–brain barrier; some of these drugs, such as
diphenhydramine and
doxylamine, may therefore be used to treat
insomnia. H1-antihistamines can also reduce inflammation, since the expression of
NF-κB, the transcription factor the regulates inflammatory processes, is promoted by both the receptor's constitutive activity and agonist (i.e.,
histamine) binding at the H1 receptor. •
Chlorpheniramine •
Chlorpromazine (low-potency
typical antipsychotic, also used as an
antiemetic) •
Chlorprothixene (low-potency
typical antipsychotic, trade name: Truxal) •
Chloropyramine (first generation antihistamine marketed in
Eastern Europe) •
Cinnarizine (also used for
motion sickness and
vertigo) •
Clemastine •
Clomipramine (
tricyclic antidepressant) •
Clozapine (
atypical antipsychotic; trade name: Clozaril) •
Cyclizine •
Cyproheptadine •
Desloratadine •
Dexbrompheniramine •
Dexchlorpheniramine •
Dimenhydrinate (used as an
antiemetic and for
motion sickness) •
Dimetindene •
Diphenhydramine (Benadryl) •
Dosulepin (
tricyclic antidepressant) •
Doxepin (
tricyclic antidepressant) •
Doxylamine (most commonly used as an
over-the-counter sedative) •
Ebastine •
Embramine •
Fexofenadine (Allegra/Telfast) •
Fluoxetine •
Hydroxyzine (also used as an
anxiolytic and for
motion sickness; trade names: Atarax, Vistaril) •
Imipramine (
tricyclic antidepressant) •
Ketotifen •
Levocabastine (Livostin/Livocab) •
Levocetirizine (Xyzal) •
Levomepromazine (low-potency
typical antipsychotic) •
Loratadine (Claritin) •
Maprotiline (
tetracyclic antidepressant) •
Meclizine (most commonly used as an antiemetic) •
Mianserin (
tetracyclic antidepressant) •
Mirtazapine (
tetracyclic antidepressant, also has antiemetic and appetite-stimulating effects; trade name: Remeron) •
Olanzapine (
atypical antipsychotic; trade name: Zyprexa) •
Olopatadine (used locally) •
Orphenadrine (a close relative of diphenhydramine used mainly as a skeletal muscle relaxant and anti-Parkinsons agent) •
Periciazine (low-potency
typical antipsychotic) •
Phenindamine •
Pheniramine •
Phenyltoloxamine •
Promethazine (Phenergan) •
Pyrilamine (crosses the blood–brain barrier; produces drowsiness) •
Quetiapine (
atypical antipsychotic; trade name: Seroquel) •
Rupatadine (Alergoliber) •
Setastine (Loderix) •
Setiptiline (or teciptiline, a
tetracyclic antidepressant, trade name: Tecipul) •
Trazodone (SARI antidepressant/anxiolytic/hypnotic with mild H1 blockade action) •
Tripelennamine •
Triprolidine H2-antihistamines H2-antihistamines, like H1-antihistamines, exist as
inverse agonists and neutral
antagonists. They act on
H2 histamine receptors found mainly in the
parietal cells of the
gastric mucosa, which are part of the endogenous signaling pathway for
gastric acid secretion. Normally, histamine acts on H2 to stimulate acid secretion; drugs that inhibit H2 signaling thus reduce the secretion of gastric acid. H2-antihistamines are among the first-line therapy to treat
gastrointestinal conditions, including
peptic ulcers and
gastroesophageal reflux disease. Some formulations are available over the counter. Most side effects are due to cross-reactivity with unintended receptors. Cimetidine, for example, is notorious for antagonizing androgenic testosterone and DHT receptors at high doses. Examples include: •
Cimetidine •
Famotidine •
Lafutidine •
Nizatidine •
Ranitidine •
Roxatidine •
Tiotidine H3-antihistamines An
H3-antihistamine is a classification of
drugs used to inhibit the action of
histamine at the
H3 receptor. H3 receptors are primarily found in the brain and are inhibitory
autoreceptors located on histaminergic nerve terminals, which modulate the release of
histamine. Histamine release in the brain triggers secondary release of excitatory neurotransmitters such as
glutamate and
acetylcholine via stimulation of H1 receptors in the
cerebral cortex. Consequently, unlike the H1-antihistamines which are sedating, H3-antihistamines have
stimulant and cognition-modulating effects. Examples of selective H3-antihistamines include: •
Clobenpropit •
ABT-239 •
Ciproxifan •
Conessine •
A-349,821. •
Thioperamide H4-antihistamines H4-antihistamines inhibit the activity of the
H4 receptor. Examples include: •
Thioperamide •
JNJ 7777120 •
VUF-6002 == Atypical antihistamines ==