<unk>  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<unk>  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.<unk>  does also act as FIASMA (functional inhibitor of acid sphingomyelinase).<unk>  is rapidly absorbed from the gastrointestinal tract and peak plasma concentrations are attained in 2–4 hours. Antihistamines are thought to be metabolized in the liver, mostly by mono-/didemethylation and glucuronide conjugation. It is an inhibitor of cytochrome P450 CYP2D6 and may interfere with other drugs metabolized by this isozyme.
Clemastine
Ebastine
Azelastine
Pemirolast
Ergotamine
Hydrastine
Altretamine
Dihydroergotamine