ATC Group: D04AA Antihistamines for topical use

Clemastine is an H₁-receptor antagonist. It inhibits selectively the histamine receptors of the H₁ type and reduces capillary permeability. It exerts a potent antihistaminic and antipruritic effect with a fast onset and long duration of action.

Dimetindene is an antihistaminic of the alkylamine group. Its action is the result of the capture of histamine Η₁ subunits. It has mild anticholinergic and sedative action.

Diphenhydramine is an ethanolamine-derivative antihistamine. It is an antihistamine with anticholinergic and marked sedative effects. It acts by inhibiting the effects on H₁-receptors. Diphenhydramine is effective in reducing sleep onset (i.e., time to fall asleep) and increasing the depth and quality of sleep.

Mepyramine is a first generation antihistamine, targeting the H1 receptor. However, it rapidly permeates the brain and so often causes drowsiness as a side effect. Mepyramine is a histamine H1 receptor inverse agonist. It binds to a G protein-coupled form of the receptor and promotes a G protein-coupled inactive state of the H1 receptor that interferes with the Gq/11-mediated signaling. Mepyramine competes with histamine for binding at H1-receptor sites on the effector cell surface, resulting in suppression of histaminic edema, flare, and pruritus. The sedative properties of mepyramine occur at the subcortical level of the CNS. It has mild hypnotic properties and some local anesthetic action and is used for allergies (including skin eruptions) both parenterally and locally. It is a common ingredient of cold remedies.

Promethazine is a potent, long acting, antihistamine with additional anti-emetic central sedative and anti-cholinergic properties.