Delivery system intravitreal

The main drawbacks associated with liposomes are their short shelf life and difficulty in storage, limited drag-loading capacity and instability on sterilization and finally, transient blurring of vision after an intravitreal injection. Despite these disadvantages, they have a potential as drag delivery systems as they are composed of substances that are non-toxic and totally biodegradable. 

Various colloidal systems have been studied for use as potential ophthalmic delivery systems, including liposomes and nanoparticles. Liposomes are bioerodible and biocompatible systems consisting of microscopic vesicles composed of lipid bilayers surrounding aqueous compartments. Liposomes have demonstrated prolonged drug effect at the site of action but with reduced toxicity. Ophthalmic studies have included topical, subconjunctival, and intravitreal administration, but no commercial preparations are currently available for ophthalmic use. 

The success of intravitreal implants, such as achieved with ganciclovir, has renewed interest in developing an intravitreal corticosteroid implant to further enhance the intravitreal route of administration, thus reducing the need for multiple injections. Bausch and Lomb and Control Delivery Systems have developed an intravitreal implant that can deliver the corticosteroid fluocinolone acetonide (Retrisert) to posterior eye tissue for up to 3 years. The implant, which was approved in 2005 by the U.S. Food and DrugAdministration (FDA), delivers 0.59 or 2.1 mg of fluocinolone acetonide. The long-term ocular side effects of this device are unknown at this time. 

Recently, macular edema associated with uveitis (29), diabetic retinopathy (30), and central retinal vein occlusion (31,32) has been treated with intravitreal injection of triamcinolone acetonide. Macular edema decreased after treatment but recurred three to six months after injection. A sustained-release steroid delivery system may be more attractive than a simple injection of triamcinolone as it could reduce or eliminate the need for multiple intravitreal injections. 

Shalaby, M. and Shalaby, S. W., Intravitreal treatment of cytomegalovirus retinitis and need for controlled release systems, in Tailored Polymeric Materials for Controlled Delivery Systems, McCullock, I. and Shalaby, S. W., Eds., ACS Symposium Series, American Chemical Society, Washington, DC, 1998. Friedberg, D. N., Cytomegalovirus retinitis diagnosis and status of systemic therapy, /. AIDS Hum. Retrovirol., 14(1), SI, 1997. 

Kuppermann, B.D. Blumenkranz, M.S. Haller, J.A. Williams, G.A. Weinberg, D.V. Chou, C. Whitcup, S.M. Randomized controlled study of an intravitreous dexamethasone drug delivery system in patients with persistent macular edema. Arch. Ophthalmol. 2007,125 (3), 309-317. 

Chhablani et al. showed that in oxidized PSi covalently loaded daunorubicin demonstrated sustained intravitreal release for 3 months without any evidence of toxicity, while physisorbed daunorubicin was released within 2 weeks and localized retinal toxicity were observed due to high daunorubicin concentration. Wu et al. added a new functionality to PSi dmg delivery system (Wu et al. 2011). They used 1-dimensional porous silicon photonic crystal in intravitreal delivery. The reflectance spectrum of the crystal (i.e., color) changed from red to green as daunombicin was releasing enabling real-time monitoring of the drag release proeess. These types of multifunctional delivery systems based on versatile properties of PSi are expeeted to be published much more in future. 

Hou H, Nieto A, Ma F, Freeman WR, Sailor MJ, Cheng L (2014) Tunable sustained intravitreal drug delivery system for daunorubicin using oxidized porous silicon. J Control Release 178 46-54 Hull R (1999) Properties of crystalline silicon, vol 20, EMIS datareview series. lEE Press, London Ilyas S, Gal M (2006) Gradient refractive index planar microlens in Si using porous silicon. Appl Phys Lett 89 211123... 

X. Dong, W. Shi, G. Yuan, L. Xie, S. Wang, and P. Lin, Intravitreal implantation of the biodegradable cyclosporin A drug delivery system for experimental chronic uveitis, Graefes Arch. Clin. Exp. Ophthalmol, 244 (4), 492-497, 2006. 

In intravitreal injection, medicines are introduced directly into the vitreous fluid through pars plana the medicines are introduced into the vitreous either as a solution or a depot formulation or dispersion of microparticles although this route is preferred for posterior segment, it has limitations, because it requires repetitive injections which can cause retinal detachment, cataract, hyperemis and endophtalmitis, which can be avoided by sustained release drug delivery systems and promote patient compliance. 

S.L. Fialho, F. Behar-Cohen, and A. Silva-Cunha, Dexamethasone-loaded polyje-caprolactone) intravitreal implants A pilot study, Eu / Pharm Biopharm, 68,637-646,2008. G. Giavaresi, M. Tschon, V. Borsari, J.H. Daly, J.J. Liggat, M. Fini, V. Bonazzi, A. Nicolini, A. Carpi, M. Morra, C. Cassinelli, and R. Giardino, New polymers for drug delivery systems in orthopaedics In vivo bio compatibility evaluation, Biomed Pharmacother, 58, 411-417,... 

Sustained delivery of ophthalmic medications is a novel approach in treating chronic intraocular infections in conditions where systemic administration is accompanied by undesirable side-effects and repeated intravitreal injections carry the risk of infection. The administration of medications by implants or depot devices is a very rapidly developing technology in ocular therapeutics. The various types of implant and mechanisms of drug release have been discussed in general in Chapter 4. 

Vitrasert (ganciclovir) a nondegradable intravitreal system for localized delivery of ganciclovir over 6 months for patients with cytomegalovirus retinitis. 

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