Clemastine

Clemastine, also known as meclastin, is an antihistamine and anticholinergic. Unlike loratadine or fexofenadine, clemastine is a sedating antihistamine, however it exhibits fewer side effects than most of the widely used antihistamines. Clemastine is also classified as an antipruritic (i.e. it stops itching).

Pharmacology

Clemastine is an antihistamine with anticholinergic and sedative effects. Antihistamines competitively bind to histamine receptor sites, thus reducing the neurotransmitter's effects. Effects of histamine (which are countered by antihistamines) include:

• Increased capillary permeability
• Increased capillary dilatation
• Edema (i.e. swelling)
• Pruritus (Itch)
• Gastrointestinal/respiratory smooth muscle constriction

Clemastine inhibits both the vasoconstrictor and vasodilator effects of histamine. Depending on the dose, the drug can produce paradoxical effects, including CNS stimulation or depression.

Most antihistamines exhibit some type of anticholinergic activity. Antihistamines act by competitively binding to H1- receptor sites, thus blocking the binding endogenous histamine. Antihistamines do not chemically inactivate or prevent the normal release of histamine.

Clemastine is rapidly absorbed from the gastrointestinal tract and peak plasma concentrations are attained in 2-4 hours.

Mechanism of Action

Clemastine is a selective histamine H1 antagonist. It binds to the histamine H1 receptor, thus blocking the action of endogenous histamine, which leads to...
Read More