Emedastine is a relatively selective H1-receptor antagonist.
Mechanism of action
Emedastine is a relatively selective, histamine H1 antagonist. In vitro examinations of emedastine's affinity for histamine receptors demonstrate relative selectivity for the H1 histamine receptor. In vivo studies have shown concentration-dependent inhibition of histamine-stimulated vascular permeability in the conjunctiva following topical ocular administration. Emedastine appears to be devoid of effects on adrenergic, dopaminergic and serotonin receptors.
Ophthalmic use of emedastine usually does not produce measurable plasma concentrations.
Volume of distribution
Two primary metabolites, 5-hydroxyemedastine and 6-hydroxyemedastine, are excreted in the urine as both free and conjugated forms. The 5'-oxoanalogs of 5-hydroxyemedastine and 6-hydroxy-emedastine and the N-oxide are also formed as minor metabolites.
Approximately 44% of the oral dose is recovered in the urine over 24 hours with only 3.6% of the dose excreted as parent drug. Two primary metabolites, 5- and 6-hydroxyemedastine, are excreted in the urine as both free and conjugated forms.
The elimination half-life of oral emedastine in plasma is 3-4 hours.
Somnolence and malaise have been reported following daily oral administration.
This compound belongs to the class of chemical entities known as benzimidazoles. These are organic compounds containing a benzene ring fused to an imidazole ring (five member ring containing a nitrogen atom, 4 carbon atoms, and two double bonds).
In peripheral tissues, the H1 subclass of histamine receptors mediates the contraction of smooth muscles, increase in capillary permeability due to contraction of terminal venules, and catecholamine release from adrenal medulla, as well as mediating neurotransmission in the central nervous system.
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