CLINICAL PHARMACOLOGY
Emedastine is a relatively selective, histamine H1 antagonist. In vitro examinations of emedastine’s affinity for histamine receptors (H1: Ki=1.3 nM, H2: Ki=49,067 nM, and H3: Ki=12,430 nM) 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.
Following topical administration in man, emedastine was shown to have low systemic exposure. In a study involving 10 normal volunteers dosed bilaterally twice daily for 15 days with emedastine ophthalmic solution 0.05%, plasma concentrations of the parent compound were generally below the quantitation limit of the assay (<0.3 ng/mL). Samples in which emedastine was quantifiable ranged from 0.30 to 0.49 ng/mL. The elimination half-life of oral emedastine in plasma is 3-4 hours. 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 5’-oxoanalogs of 5- and 6-hydroxyemedastine and the N-oxide are also formed as minor metabolites.
In an environmental study, patients with allergic conjunctivitis were treated with EMADINE® (emedastine difumarate ophthalmic solution) 0.05% for six weeks. The results demonstrated that EMADINE® (emedastine difumarate ophthalmic solution) 0.05% provides relief of the signs and symptoms of allergic conjunctivitis.
In conjunctival antigen challenge studies, in which subjects were challenged with antigen both initially and up to four hours after dosing, EMADINE® (emedastine difumarate ophthalmic solution) 0.05% was demonstrated to be significantly more effective than placebo in preventing ocular itching associated with allergic conjunctivitis.
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