Ophthalmic therapeutics bioavailability

Furthermore, addition of a penetration enhancer to the vehicle of an ophthalmic solution has been used to reduce the size of the drop instilled. Since this reduction in drop size results in a decreased washout and systemic drug loss, this would result in a decreased potential for systemic toxicity, at the same time improving the ocular absorption of poorly absorbed drugs [109], Therefore, improved ocular bioavailability and therapeutic response could be obtained. 

Until recently, the topical ophthalmic use of some interesting and promising either lipophilic or macromolecular therapeutic substances has been limited clinically because of their restrictive physicochemical properties, which has exhibited poor ocular bioavailability. It is possible... 

Emulsions have been used for centuries for the oral administration of medical oils and vitamins and as dermatological vehicles. Recently, their application has been extended as drug carriers in the delivery and targeting of ophthalmic drags. An indomethacin emulsion has been reported to increase ocular bioavailability and efficacy compared to commercially available formulation in rabbits. 0.4% indomethacin emulsion showed 2.2 fold increase in the area under the anterior aqueous drag concentration/time curve compared to a 1% indomethacin suspension. The emulsion formulation also reduced ocular surface irritation caused by indomethacin Similar advantages have been shown for a pilocarpine emulsion which produced a prolonged therapeutic effect in comparison with pilocarpine hydrochloride eyedrops in man. It can be administered only twice a day, rather than four times daily for conventional formulation. 

Frequent instillation of solution or higher drug concentration is needed to achieve the desired therapeutic response. But this attempt is potentially dangerous if drug solution drained from the eye is systemically absorbed from the nasolacrimal duct. To increase precorneal residence time and ocular bioavailability, different ophthalmic delivery systems such as viscous solutions, ointments, gels, suspensions, or polymeric inserts are used. But because of blurred vision (e.g., ointments) or lack of patient compliance (e.g., inserts), these formulations have not been widely accepted. 

Although satisfactory therapeutic results are obtained with usual topical ophthalmic drug (topical ocular solutions and ointments) they present some inconveniences pt. Bioavailability is poor, requiring high doses and repeated applications. 2 . Diffusion of the drug into the bloodstream across de nasal mucosa which is continuous with the conjuntival sac, represents an additional risk of systemic toxicity. (Chang and Lee, 1987, Salminen,1990). 

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