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Abstract Tropisetron is one of the 5-HT3 receptor antagonists, reported to be effective in the prophylaxis of acute chemotherapy-induced nausea and vomiting (CINV). Tropisetron as the hydrochloride salt (TRO) is available in the pharmaceutical market, under the trade name Navoban® produced by Novartis Pharmaceuticals Ltd, in the form of hard gelatin capsules containing drug dose equivalent to 5 mg of the base as well as ampoules (2 or 5 mL) containing doses equivalent respectively to 2 or 5 mg of the base. Due to first-pass metabolism in the liver, the absolute bioavailability of TRO is about 60%. However, it suffers from phenotypic variability in hepatic metabolism due to genetic polymorphism of the cytochrome P450 enzyme, thus generating population of either poor or extensive TRO metabolizers. Headache and constipation with abdominal pain are the main adverse effects associated with recurrent TRO administration. Therefore, it could be assumed that the transdermal route would be advantageous to deliver TRO over the oral and parenteral ones; by avoiding drug first pass effect, reducing gastrointestinal side effects, improving drug bioavailability as well as patient convenience and compliance. Hence, the purpose of work in this thesis was to formulate, optimize, and in vitro/in vivo evaluate TRO-loaded ethosomes and flexosomes (Flex), considered as novel ultra-deformable vesicular systems for enhanced transdermal delivery. Firstly, TRO-loaded ethosomes were prepared by the “hot” technique. The effect of different formulation variables, phospholipid (A) and ethanol concentrations (B), and exclusively the type of phospholipid (C) either egg phosphatidylcholine (EPC) or soybean phosphatidylcholine (SPC) were prepared using 3×22 full factorial design and then optimized using the desirability function. The entrapment efficiency (EE%, Y1), vesicle size (VS, Y2), polydispersity index (PDI, Y3), and zeta potential (ZP, Y4) were the responses studied. Predictive modelling of such responses was generated and confirmed. The ex-vivo drug permeation across rat skin from the selected formulations was investigated associated with the determination of various permeation parameters (Q24, Jss, Kp, and D) as well as permeation kinetics. Particle morphology using HR-TEM, drug– excipient interactions, and vesicle stability were also explored. The results proved the critical contributions of all formulation variables on the ethosomal characteristics. The suggested equation models for EE%, VS, and PDI responses showed good predictability. Only the concentration of phospholipid, irrespective to PC type, had a significant effect on the transdermal flux (p<0.01). All formulations followed zero order permeation kinetics. The ethosomal vesicles were nearly spherical in shape. Drug amorphization and compatibility with phospholipids were confirmed by DSC and FT-IR, respectively. EPC-based ethosomes proved good stability. The ethanolic vesicular formula (E-4), composed of 3 and 40% of EPC and ethanol, respectively, was chosen considered as a novel potential nanocarrier for accentuated transdermal TRO delivery. Aiming to ameliorate the transdermal permeation of TRO through the skin, the novel ultra-deformable vesicular system (Flex) was developed, based on the composition of the selected ethosomal formula. Flex were prepared by the previously applied ‘hot’ method with some modifications. A systematic optimization process was adopted where the edge activator (EA) type, PC:EA molar ratio, and cholesterol concentration were the variables studied. Various EA types, such as the cationic cetyl trimethylammonium bromide (CTAB), the anionic sodium cholate (NaC) and sodium deoxycholate (SDC), and the non-ionic tween 80 (T80), D-α-Tocopherol polyethylene glycol 1000 succinate (TPGS), cremophor RH 40 (CREM) and Span 85 were all tried at different PC:EA molar ratios (5:1, 2:1, 1:1), without and with the inclusion of various cholesterol concentrations (0.1, 0.2, 0.3%w/v). The prepared formulations were subjected to visual inspection aiming to describe and anticipate the formed systems, further confirmed with turbidity measurements. Moreover, the particle size (PS), PDI, and ZP were determined. The drug EE%, ex-vivo permeation study across rat skin and permeation kinetics were performed on the selected Flex. Besides, the permeation enhancing mechanisms of the selected ethanolic vesicles were assessed on isolated stratum corneum (SC) from rat skin applying the DSC technique on the dried treated SC samples. The morphologies of the selected Flex based on TPGS and CREM were determined using HR-TEM. Drug-excipient interaction studies were also executed using DSC and FT-IR. Finally, the selected Flex were stored under refrigeration (5 ±3◦C) for a period of 6 months for physical stability testing. The effect of storage on PS, PDI, ZP, and EE% of TPGS-Flex, CREM-Flex as well as E-4 was assessed at different time intervals. The results revealed that all variables strongly affected the studied responses. CTAB, T80, TPGS, and CREM-based Flex, all prepared at 2:1 PC:EA molar ratio and 0.1 %w/v cholesterol, were the optimized Flex formulae. Both TPGS and CREM-based Flex showed the highest EE% and the prominent enhancement of exvivo transdermal TRO permeation through rat skin. DSC analysis of treated SC samples showed the additive effect of EAs in ethosomes for enhanced skin permeation via lipid solubilization and denaturation of keratin filaments mechanisms. TEM images for the selected formulations showed multi-lamellar lipid stacked vesicles with almost spherical shape and defined edges. DSC results for each Flex constituents and their physical mixtures proved the dissolution and amorphization of drug crystals in the molten lipid. FTIR spectra confirmed the chemical compatibility of TRO with the vesicular constituents. Stability studies showed the increase in the diameter of CREM-based Flex, while the drug EE% showed a decline in both EA-based vesicles. Additionally and for better evaluation, in vivo assessments of the selected ethanolic vesicles were accomplished. The tracking of the selected vesicles; E-4, TPGS-Flex, and CREM-Flex, through the different layers of rat skin was executed with the aid of confocal laser scanning microscope (CLSM) after being labelled with Nile Red as a fluorescent dye. Additionally, a pharmacokinetic study was adopted aiming to test the efficacy of the prepared formulations in transdermal TRO delivery. The selected vesicles as well as an aqueous drug solution (TS) were applied topically onto rat skin and compared to a control oral solution (OS). The various pharmacokinetic parameters (Cmax, Tmax, AUC, Frel) were determined. Furthermore, a dermato-histopathological examination was performed on rat skin treated with the selected formulations (E-4, TPGS-Flex, and CREM-Flex) as well as an aqueous drug solution as a control, and the prepared histology slide images were then captured using an optical microscope. Confocal laser scanning micrographs showed that the fluorescent dye was observed deeper and higher in intensity in case of both Flex formulae rather than the ethosomal one. The pharmacokinetics study confirmed the superiority of the ethanolic vesicles, particularly Flex, in enhancing transdermal TRO delivery and hence improving its BAV compared with the oral and topical aqueous solutions. The dermato-histopathologic examinations of the rat skin showed SC detachment in case of all applied vesicles with no alterations in the underlying dermis. |