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E. Stefansson, H.H. Sigurdsson, F. Konradsdottir, T. Loftsson; Role of Topical versus Systemic Absorption in Delivery of Dexamethasone to the Anterior and Posterior Segments of the Rabbit Eye . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5088.
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1. To determine the relative importance of topical and systemic absorption in delivering drugs from eye drops the anterior and posterior segments of the eye. 2. Can dexamethasone–cyclodextrin eye drops deliver significant drug levels to the retina and vitreous?
3. To compare systemic absorption following topical eye application to intranasal or intravenous delivery.
In order to distinguish between topical and systemic absorption in the eye, we applied 0.5% dexamethasone– cyclodextrin eye drops to one (study) eye of rabbits and not in the contralateral (control) eye. Drug levels were measured in each eye. The study eye shows the combination of topical and systemic absorption, whereas the control eye shows the result of systemic absorption only.
In the aqueous humor dexamethasone levels were 170 ± 76 ng/g (mean ± SD) in the study eye and 6 ± 2 in the control eye and similar ratios were seen in the iris and ciliary body(see figure). In the retina the dexamethasone level was 33 ± 7 ng/g in the study eye and 14 ± 3 in the control eye and a similar ratio was seen in the vitreous (see figure).
After topical application topical absorption dominates in the anterior segment. Topical absorption also plays a significant role in delivering dexamethasone to the posterior segment of the eye. In the case of retina 40% of the drug reaches retina via systemic route and 60% via topical penetration (see figure). Dexamethasone–cyclodextrin eye drops deliver significant amount of drug to the retina.
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