possibility of modulating their erosion rate by modifying their final structure during synthesis, and by addition of anionic or cationic surfactants. A crosslinked gelatin insert was used by Attia et al.229 in order to increase bioavailability of dexamethasone in the rabbit eye. The dexamethasone levels in the aqueous humor were found to be 4fold greater compared to a dexamethasone suspension. More recently, Gelfoam® devices containing pilocarpine were tested in rabbits.266 These devices are made of absorbable gelatin sponges of 2.5 X 2.5 X 1.0 mm sorbed with pilocarpine to form a matrix. The application of the device in the lower conjunctival sac produces a 2-3-fold increase in the duration of effect of pilocarpine over conventional eyedrops and gels.
The disadvantage of erodible systems is that they can have significantly variable erosion rates based on individual patient physiology and lachrymation patterns. In addition, degradation products and residual solvents used during the polymer preparation can cause inflammatory reactions.
IV.B.4. Concluding comments on ocular inserts as drug delivery systems In conclusion, the majority of therapeutic agents used in the eye can be delivered using ocular inserts. Such delivery systems are a promising alternative to classical dosage forms because of their various advantages. However, only a few insert preparations have been commercialized. This can be attributed to the reluctance of ophthalmologists, patients and owners of animals to replace the traditional ophthalmic solutions as well as the cost and the need to train both the prescribers, patients and owners of animals to place the inserts correctly in the eyes.
In the future, the use of ophthalmic inserts will certainly increase because of the development of new polymers, the emergence of new drugs having short biological half-lives or systemic side effects and the need to improve the efficacy of ophthalmic treatments by ensuring an effective drug concentration in the eye for several days.
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