الفهرس 
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Abstract
Background:
The poor bioavailability and therapeutic response exhibited by conventional eye drops due to rapid precorneal elimination of the drug may be overcome by the use of ocular drug delivery system that sustain drug release and reserve drug dose from precorneal factors. The delivery system used in this study, e.g. biodegradable polymeric nanoparticles and in situ gels which have desired features such to enhance the stability of drugs/proteins and possess useful controlled release (CR) properties. Also, studied are the in situ gelling systems that are instilled as drops into the eye that undergo a sol-to-gel transition in the cul-de-sac. Hence, the purpose of the present work was to formulate and evaluate an ophthalmic delivery system for ketorolac tromethamine (KT), based on the concept of controlled release as well as thermally in situ gelation. Ketorolac tromethamine (KT) is a non-steroidal anti-inflammatory drug (NSAID) from the family of heterocyclic acetic acid derivatives. It is effective in inhibiting post-operative eye inflammation, reducing conjunctivitis with no alteration of corneal opacity; also it has been shown to increase intraocular pressure. Topical ketorolac was a more effective inhibitor of miosis than topical diclofenac sodium during cataract surgery. Only small amount of instilled dose (1-3%) of ophthalmic solution of KT penetrates the cornea and reaches intraocular tissues. Substantial efforts have been directed toward the development of ocular drug delivery systems that would prolong the drug retention, allowing the drug to remain in contact with the cornea for a prolonged time and thus increases bioavailability. Nanoparticles (NPs) and thermally responsive in situ gels for ophthalmic drug delivery have been shown to enhance ocular bioavailability while providing sustained release action. Furthermore, these drug delivery systems are advocated as ophthalmic drug delivery systems that may enhance dosage form acceptability while providing sustained release action.
Objective:
The aim of this work is to design and characterise a drug delivery system formulations for ocular delivery of KT that has the convenience of being delivered as eye drops and yet enhance the drug retention and potentially increase the ocular bioavailability.
Methodology:
An HPLC method was developed and validated for KT; preformulation studies were performed to study the physicochemical properties of KT, such as aqueous solubility, lipid solubility (lipid/water partition coefficient), melting behaviour, and spectrometric identification and drug-polymer interactions. Polymeric NPs were prepared using different polymers such as chitosan (CS), sodium tripolyphosphate (TPP), sodium alginate (SA).The effect of different concentration of these polymers on particle size, zeta potential, entrapment efficiency (EE%) and release profile of prepared NPs were determined. Also, a combination of thermo-responsive polymers such as poloxamer 407 (P407), and poloxamer 188 (P188) and different combinations of CS, methyl cellulose (MC) with P407 were studied. The effect of different polymer combinations on gelation temperature, gelation time, rheological properties and texture analysis profiles of these formulations were determined. A few promising formulations were chosen for the investigation of in vitro release profile of KT from these systems. selected NPs were also dispersed within the in situ gel and the texture analysis profiles as well as the release pattern were investigated. Accelerated physical stability study were carried out separately on selected CS-based NPs formulations and different in situ gels for a period of three months. Also, mucoadhesion test was carried out on both types of formulations by two different methods. Furthermore, the spreading ability of selected KT loaded NPs formulations as well as in situ gels were performed by measuring the surface tension as well as the contact angle for these preparations. selected formulations of both NPs as well as in situ gels loaded with KT which meet the required criteria were prepared and evaluated for ex vivo transcorneal permeation study of KT, ocular irritation using the hen’s egg chorioallantoic membranes (HET-CAM) and BCOP tests, and finally tissue culture examination include MTT cytotoxicity assay.
Results and discussion:
HPLC method was developed and validated for KT. The preformulation studies showed that KT is a hydrophilic drug with a log P value of 1.61 at 35oC. Acid degradation, alkali and oxidative degradation is the main degradation route for KT which confirms that the method validated is stability indicating. The solubility of the drug was pH-dependent as increased with increasing the pH. The lipid /water partition coefficient data demonstrated the dependency of the D value on the pH of the medium. The DSC chromatograms and FT-IR spectra revealed that there was no chemical interaction between drug and CS suggesting that the drug is dispersed in a soluble form inside the NPs. In addition, SEM images of NPs revealed that the NPs were spherical in shape and confirm also the uniformity of particle size distribution. EE% of different NP formulations increased with increasing concentration of KT; also, the KT-loaded NP formulation exhibited stability and mucoadhesive characteristics when tested with mucin. Furthermore, in vitro drug released profile showed that the NPs have ability to sustain drug release compared to drug solution. For in situ gel formulations, different concentrations of CS and MC have an effect on the sol-gel transition temperature as well as rheological properties of gel formulations. P407 alone have shear thickening flow behaviour while addition of CS or MC gave shear thinning effect (a pseudoplastic behavior) at different concentrations. Furthermore, most formulations were physically stable at least for three months at 4oC. In addition to that mucoadhesion study using mucin discs showed that in situ gel formulations have good mucoadhesive characteristics as upon increasing the concentration of P407 and at different concentrations of CS, MC and P188. All tested formulations demonstrated spreading ability on the corneal surface. In vitro release and ex vivo permeation experiments indicated that the in situ gels were able to prolong and control KT release compared to drug solution.The prepared formulations demonstrated minimal to no irritation potential; significantly controlled KT release; sustained drug at the ocular surface as well as delayed transcorneal permeation of KT through excised porcine corneas compared with the aqueous KT solution; and tested formulations were non-irritants to HET-CAM or BCOP tests. Finally, KT-loaded NPs and in situ gels determined by MTT assay on two different types of corneal cell line included human lens cells and human primary corneal epithelial cells showed acceptable and reasonable toxicity compared to control samples.
Conclusion:
The developed drug delivery systems were able to sustain the release of KT, control KT corneal permeation through porcine corneas, and demonstrate good ocular tolerability. These results demonstrate the potential of CS based NPs as well as in situ gel formulations in delivering KT to the ocular tissue with minimum irritation potential and toxicity effect but MTT assay on primary corneal epithelial cells and lens cells revealed that in situ gel formulations loaded with KT showed reasonable and acceptable percent cell viability compared with control samples. Generally it can be concluded from the data that KT loaded NPs as well as KT loaded in situ gel formulations are promising candidates for the ocular delivery of KT in terms of improving its efficacy and safety. In addition to being a convenient ocular delivery systems for KT across the cornea owing to the strong concentration dependence of the sol–gel transition temperature of in situ gels combined with the cytotoxic effect observed.