| Objective: Most ocular treatments call for the topical administration to introduce active drugs into the tissues around the ocular cavity. However the special physical barrier and protection mechanisms of the eye reduce the bioavailability drastically. As one of the important fields of controlled release, ophthalmic drug delivery has received extensive interests during the last two decades. The sensitivity and protection mechanisms of the eye promote more effective drug delivery systems with better compliancy to be developed, however, the applications of numerous pharmaceutical methods are limited simultaneously, which presents great challenge in designing ophthalmic dosage forms. In-situ-forming gels refer to the polymer solutions can be administrated as liquid, which undergo a phase transition to a non-crosslinked semisolid gel upon exposure to physiological environments. Most of the applications of the in-situ-forming gels are concerned with ophthalmic disease treatment for its convenient administration combined with the favorable ocular residence time. In this thesis,Compound Naphazoline Hydrochloride(CNH) was selected as the model drug,and a series of relative researches were carried out, including the drug permeability across isolated cornea, development of in-situ-forming gels with modulated phase transition temperature, characterization of gelation process by dynamic rheological method, drug release, the pharmacokinetics in aqueous humor and tear and bioavailabi- lity after the in-situ-forming gels applied topically.The in-situ-forming gels substantially increased the bioavailabi- lity of the drug, and showed great potential in ophthalmic application.Methods: The properties about Compound Naphazoline Hydrochloride were studied as an essential part of preformulation. We investigated the pH-dependent apparent partition coefficient(Papp) in n-octanol/buffer system of Naphazoline Hydrochloride, Chlorphenamine Maleate and Vitamin B12 in different pH value using the classic shake-flask method, and the drug permeability across isolated cornea was studied.On the basis of scientific literatures, The formulation screening was performed by taking sol-gel transition temperature as indices in which poloxamer 407 was used as the main base material.The release behaviors of Compound Naphazoline Hydrochloride in-situ-forming gels(CNH-ISG) were studied. The release medium was artificial tears,with membraneless dissolution model at the temperature of 34.5±0.5℃, samples were obtained at set time, and then accumulated drug release were obtained. We analyzed the release data with three models: Higuichi equation , Zero Order equation,First Order equation.The chemical and physical stability of optimal formula was investigated under following circumstances: strong light and high tempreture.The irritant effects and toxic reactions of CNH-ISG on rabbit eyes were tested. Single dosing eye irritation and multiple dosing eye irritation were observed, recorded and evaluated. The CNH-ISG (or eye drops)was topically administered to the left eyes of 6 rabbits and a solution of 0.9% saline was administered to the right eyes. All eyes were then enucleated for histopathological examination to evaluate the possible toxic reactions.Pharmacokinetics study in vivo: Rabbits were selected as laboratory animals and divided into two groups in random. One group was given CNH-ED and the other was given CNH-ISG. The rabbit tears and aqueous humors were obtained and quantified at different times after topically applying CNH-ISG and CNH eye drops to the rabbit eye. Results were expressed using high performance Liquid Chromatography (HPLC) with Ultraviolet detector. Six-point standard curve were established for Naphazoline Hydrochlo- ride, Chlorphenamine Maleate and Vitamin B12 in rabbit tears and aqueous humors, in order to calculate concentration of them. The pharmacokinetics parameters were calculated by 3p97 software. Taking Tmax , T1/2 ,Cmax and AUC as indexs, inspected the relative bioavailability of two preparations. Results: The results of the Papp and the permeability across isolated cornea showed that the permeability was increasing with the increasing of the Papp. The best pH for this preparation was 7.0 according to the relationship between Papp and pH value.By taking sol-gel transition temperature as indices, the best formulation of in-situ-forming gels was 32%P407+6% P188. In this formulation, the sol-gel transition temperature was between 29~33℃and the accumulative release profile of the drug in vitro could be distributed by First Order equation.Study of stability: Compound Naphazoline Hydrochlori- de in-situ-forming gels were investigated under different conditions of temperature and light. The result showed that the formulation was stable to light and heat.The irritant effects and toxic reactions : Single dosing and multiple dosing had no markedly influences on tested rabbit eyes ,both corneas are transparent without turbidness ,and iris clarity ,no conjunctiva hyperemia , no edema and no discharge; Histological examination showed no obvious toxic effects,and there was no significant difference on rabbit eyes between the control group and the experimental group. It was tolerated well and there were no obvious irritant effects and toxic reactions to ocular tissues.It showed that it is safety for application.Pharmacokinetics study: The pharmacokinetic paramet- ers of two groups in aqueous humors were calculated by 3p97 software and were respectively as following: The results of T-test showed significant difference between the parameters Cmax , T1/2 and AUC of the two groups (P<0.05), and the experimental group showed obvious dominance.The concentrations of Naphazoline Hydrochloride, Chlorphenamine Maleate and Vitamin B12 in rabbit tears within 180 min after applying CNH-ISG were found to be significantly higher compared with those of CNH-ED. The results of T-test showed significant difference between the parameters AUC of the two groups (P<0.05), and the experimental group showed significantly higher compared with the control group.Conclusions: The results in vitro and in vivo showed that the in-situ-forming gels could prolong the residence time of drug in the ocular cavity. It was tolerated well and there were no obvious toxic effects to ocular tissues. The ISG-CNH, which upon exposure to physiological conditions will shift the gel phase , can significantly extend CNH release and increase the precorneal residence time of the drug , thus enhance ocular bioavailability compared with ISG-CNH, and showed great potential in ophthalmic application. |
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