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D. Yu, D. Tang-Liu; Ocular Administration of Epinastine to Patients With Allergic Conjunctivitis: Pharmacokinetics and Safety Profile . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3731.
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Purpose: This single-center, open label study investigated tear and plasma pharmacokinetics and the safety profile of ophthalmic epinastine, a new generation histamine H1 receptor antagonist with mast cell stabilization activity. Methods: Patients diagnosed with allergic conjunctivitis (N=14) instilled 1 drop of epinastine hydrochloride 0.05% in both eyes once on day 0, BID on days 1-6, and TID on day 7. Blood samples were taken on days 0, 1, and 4 through 7. Tears were collected on day 7. A validated LC-MS/MS assay quantitated epinastine in samples. Results: Epinastine achieved Cmax = 21.1 ± 46.2 µg/mL (mean ± SD) in tears 2 minutes after instillation. Epinastine concentrations in plasma were approximately 1 million times less in tears, near the lower limit of quantitation for the assay, 0.01 ng/mL. Epinastine plasma concentration was 0.025 ± 0.008 ng/mL after a single dose, and 0.042 ± 0.014 ng/mL after BID dosing on day 6. AUC0-infinity following a single dose was 0.465 ± 0.216 ng.hr/mL and steady state AUC0-12 (on day 6 after BID dosing for days 1-5) was 0.347 ± 0.119 ng.hr/mL. The similarity of the single dose and steady state AUC values suggest epinastine pharmacokinetics after ocular administration are linear. No adverse events nor any clinically relevant changes in visual acuity, biomicroscopy, ophthalmoscopy, vital signs, physical examination, or laboratory parameters were observed during the study. Conclusions: After instillation of epinastine HCl 0.05% ophthalmic solution, high drug concentrations were rapidly achieved at the ocular surface, the site of ocular allergy pathology. Topical administration resulted in very low epinastine concentrations in plasma, minimizing the possibility of systemic side effects.
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