الفهرس 
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Abstract
Nowadays, there is a growing interest in developing oral dosage forms that can be targeted in the GIT. Targeting can be approached from two angles, either to exert the pharmacologic response to a specific site or to utilize a specific site on the alimentary canal for drug absorption without being affected by the GIT fluid, pH fluctuation, enzymes and microflora, while travelling along the GIT.
Metronidazole is an antibiotic and antiprotozoal drug used for the treatment of infections involving anaerobic bacteria as well as protozoa! infections such as Helicobacter pylori infections, giardiasis, intestinal and extraintestinal amoebiasis due to E.histolytica, pseudomembranous colitis, Trichomonas vaginalis infection, bacterial vaginosis, and rosacea.
The aim of this thesis was to develop various Metronidazole delivery systems using different techniques and polymers with numerous potential benefits over conventional forms to act in different desired sites of the gastrointestinal tract.
The work in this thesis was divided into three chapters:
Chapter I: Formulation and evaluation of Metronidazole gastroretentive floating delivery systems.
Chapter II: Formulation and evaluation of tablets delivering Metronidazole to different parts of the gastrointestinal tract.
Chapter III: Formulation and evaluation of Metronidazole colon specific delivery systems.
Chapter I: Formulation and evaluation of Metronidazole gastroretentive floating delivery systems
The objective of this chapter was to develop a new Metronidazole floatable drug delivery system for possible localization of the antibiotic in the stomach to effectively act on Helicobacter pylori.
Floating tablets and capsules were prepared for this purpose using a blend of different polymers namely sod. alginate, chitosan, guar gum and ethyl cellulose.
Results obtained showed that:
1- The most successful tablet mixture regarding floatation obtained after several preliminary trials consisted of 1:4, ethyl cellulose: sod. alginate, together with a gas generating agent CaCO3 and a hyDROPhobic excipient, Mag. stearate (F1).
2- Tablet formulation F1 showed better floating ability and a more sustained release profile, compared to F2 and F3 containing 1:1 and 4:1 ethyl cellulose: sod. alginate respectively.
3- Capsules containing either sod. alginate, guar gum or a blend of chitosan: sod alginate, showed good floating characteristics. However C1, containing pure chitosan completely eroded after 4.5 hrs.
4- Capsules C6 containing 4:1 chitosan: sod alginate, showed good floating ability and good sustained release properties.
5- Formation of a solid dispersion between Metronidazole and increased amount of stearic acid improved floating characteristics and sustained release profile in both tablet F1 and capsules (C2 & C3) containing sod. alginate and guar gum respectively.
6- The effect of formation of solid dispersion using stearic acid on retardation of drug release was more pronounced in capsules than in tablets.